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What is a decibel?
A unit used in electrical engineering and acoustics to express on a logarithmic scale the ratio between two values with the same dimensions.
What are the quantities compared using decibels?
Two voltages, two power levels, two sound pressure levels, and so on.
What are the three factors that affect the extent of damage to hearing caused by noise?
1. Decibel level (how loud the sound is) 2. Distance (how close you are to the source of the sound) 3. Time (the length of time you are exposed to the sound)
How is sound measured?
Sound is measured in units called decibels (dB).
What is the significance of A-weighted decibels (dBA)?
A weighted decibels can be used to describe sound based on what human ears can actually hear, as people can't hear all frequencies or pitches of sound.
What decibel level is generally considered safe for sounds?
Sounds at or below 70 dBA are generally considered safe.
At what decibel level is sound more likely to damage hearing over time?
Any sound at or above 85 dBA is more likely to damage hearing over time.
What is the increased risk for hearing loss associated with noise levels of 85 dBA or higher?
People exposed to such noise levels over long periods are at a much greater risk for hearing loss.
Why are some workers required to wear hearing protectors like earplugs or earmuffs?
To protect their hearing from noise levels at or above 85 dBA while they are on the job.
What decibel level is generally considered safe for human ears?
Sounds at or below 70 dBA
At what decibel level are sounds more likely to damage hearing over time?
Any sound at or above 85 dBA
What is the risk for hearing loss for people exposed to noise levels at 85 dBA or higher over long periods of time?
Much greater risk
Why are some workers required to wear hearing protectors like earplugs or earmuffs on the job?
To protect their hearing from exposure to high decibel levels
What are some factors that affect hearing loss?
Decibel level, distance, and time
What is the decibel level of many devices that children use today?
Higher than 85 dBA
How intense is 110 dBA compared to 85 decibels?
More than 100 times as intense
Are manufacturers required to limit the maximum sound output of music devices?
No, they are not required to do so
What can volume limiting controls on devices help with?
Setting the maximum volume to a safe level
How does the sound level change as you move closer or further away from the source?
It gets louder as you move closer and softer as you move away
In what situation at a concert can reduce the risk of hearing damage?
Sitting away from the speakers
What impact does exposure to loud sounds on a regular basis have on the risk of hearing damage?
It increases the risk for permanent damage over time
What is considered safe sound levels that last a long time?
Sounds at or below 70 dBA
At what decibel level and duration is it more likely for noises to damage hearing?
85 dBA lasting a few hours, 100 dBA lasting at least 14 minutes, 110 dBA lasting at least 2 minutes
Why is decibel notation mainly used in calculating signal levels?
It is convenient for calculating signal levels
What is the risk of permanent damage to hearing if exposed to loud sounds on a regular basis?
Increases over time
What is the potential effect of a single but long-lasting loud event on hearing?
Can cause damage
What is the considered safe level for sounds that last a long time?
70 dBA or below
At what sound level and duration are noises more likely to damage hearing?
85 dBA for a few hours, 100 dBA for at least 14 minutes, 110 dBA for at least 2 minutes
What is the main reason for using decibel notation in calculating signal levels?
Convenience
When working with decibel values, what operation can be performed with dB values?
Decibel values can only be added or subtracted
How could the operation of adding individual gains of two amplifiers in cascade be interpreted in terms of dB?
It could be interpreted as adding the individual dB gains to get the overall gain of the combination
How could the operation of getting the net gain of an amplifier and a lossy section be interpreted in terms of dB?
It could be interpreted as subtracting the dB loss from the dB gain to get the net gain
What is correlated noise?
Unwanted electrical energy that interferes with the desired signal
What is correlated noise?
Unwanted electrical energy that is used before it is transmitted, and falls into two categories.
What are the two categories of noise?
1. Correlated noise 2. Uncorrelated noise
What is noise in the context of signal transmission?
Any unwanted or undesirable signal that interferes with the desired signal.
How can noise affect a signal in the medium?
Noise can affect the signal in the medium as there is no factor to protect the signal except for the type of modulation used before transmission.
What are the two categories of noise?
1. Correlated Noise 2. Uncorrelated Noise
What is correlated noise?
Unwanted electrical energy present as a direct result of a signal, such as harmonic and intermodulation distortion.
What are the two types of correlated noise?
a. Intermodulation Distortion b. Harmonic Distortion
What is uncorrelated noise?
Noise present regardless of whether there is a signal or not.
What are the two types of uncorrelated noise?
a. External Noise b. Internal Noise
What is external noise?
Noise produced by devices or equipment made by humans that affects frequencies up to 500MHz.
What are the sources of external noise?
1. Industrial Man-Made Noise 2. Static Atmospheric Noise 3. Space (Extra Terrestrial) Noise
What is industrial man-made noise?
Noise produced by devices or equipment made by humans, affecting frequencies up to 500MHz. Example sources are combustion engines, fluorescent lamps, switches, etc.
What is static atmospheric noise?
Noise coming from lightning discharges during thunderstorms, rain, and dust storms. It greatly affects frequencies below 30MHz.
What is space (extra-terrestrial) noise?
Noise coming from sources like the sun, solar noise, stars, cosmic noise, and galaxies. It is observable between 8MHz to 143GHz.
What is solar noise?
The noise intensity produced by the sun, varying with time and having a repeating 11-year cycle. During its peak cycle, a tremendous amount of noise is produced.
How is solar noise intensity affected by the sun's activity?
Solar noise intensity varies with time and has a repeating 11-year cycle, with a peak cycle producing a significant amount of noise.
What are some examples of sources of electromagnetic noise in the environment?
Combustion engines, fluorescent lamps, switches, etc.
What is static atmospheric noise and when does it greatly affect frequencies?
Static atmospheric noise is noise coming from lightning discharges during thunderstorms and rain/dust storms. It greatly affects frequencies below 30 MHz.
What is space or extraterrestrial noise and what are some sources of it?
Space or extraterrestrial noise is noise coming from the sun, solar noise, stars, cosmic noise, and galaxies. Sources include sun, stars, cosmic noise, and galaxies.
What is solar noise and how does it affect radio signal interference during its peak cycle?
Solar noise is the noise intensity produced by the sun, which varies with time in a repeating 11-year cycle. During its peak cycle, a tremendous amount of noise is produced causing radio signal interference and making many frequencies unusable for communications.
What is cosmic noise and what frequency range does it affect the most?
Cosmic noise is noise coming from stars and affects the frequency range from 10 MHz to 15 GHz, with the greatest disruptions in the 15 to 150 MHz range. Sources include Cassiopeia A and Cygnus A.
What is internal noise and what are some names it is known by?
Internal noise is noise coming from the rapid and random motion of charge carriers inside a resistive component when heated. It is also known as Johnson noise, thermal noise, white noise, or Gaussian noise.
What is the frequency range affected by stars and cosmic sources in terms of EMF interference?
10MHz to 15GHz, with the greatest disruptions in the 15 to 150 MHz range
What are two of the strongest sources of EMF interference from stars.
Cassiopeia A and Cygnus A
What is Johnson noise, and why is it also known as thermal noise?
Noise from rapid and random motion of charge carriers in a resistive component when heated; named after J.B. Johnson and is temperature dependent
Shot Noise Definition:
Shot noise is the major contribution of transistor noise due to shot effect. Current carriers in semiconductors have a discrete particle nature.
What is the major contribution of transistor noise due to shot effect?
Shot noise
What type of noise is also known as 1f noise, flicker noise, excess noise, or modulation noise found in transistors?
PINK NOISE
What is transit time noise and where does it occur?
Transit time noise is a kind of noise that occurs in transistors. Transit time refers to the duration of time it takes for a current carrier like a hole or electron to move from input to output. The effect of this noise can be seen in high-frequency operation.
What is resistance noise and what are its contributors?
Resistance noise is due to the base, emitter, and collector internal resistance of a transistor.
What is burst noise, and where is it observed in transistors?
Burst noise, also known as popcorn noise, is a low-frequency noise observed in BJT (Bipolar Junction Transistor) that appears as a series of bursts of two or more levels.
What is avalanche noise and what causes it?
Avalanche noise is large noise spikes due to collisions that result in an avalanche action in a device.
What is partition noise?
Partition noise refers to random fluctuations in the division of current in two or more electrodes.
What is impulse noise characterized by?
Impulse noise is non-continuous, consisting of irregular pulses or noise spikes of short duration and relatively high amplitude. The spikes are called HITS (High Impulse Transient Signals).
What is avalanche noise?
Large noise spikes due to collisions that result in a valanching action.
What is partition noise?
Random fluctuations in the division of current in two or more electrodes.
What is impulse noise?
A non-continuous noise consisting of irregular pulses or noise spikes of short duration and relatively high amplitude.
What is the Signal-to-Noise Ratio (SNR) usually expressed in?
Power, because the received signal is also expressed in terms of power.
What is Noise Factor (NF), Noise Ratio (NR), and Noise Figure (F) related to?
They are related to the signal-to-noise ratio.
What is used to specify how noisy a device is in terms of noise figure?
Noise Figure
What is used to identify the noise content at a specific point but is not useful in relating how much additional noise a device has injected into a signal going from input to output?
Signal-to-Noise Ratio (SNR)
What do each amplifier in a cascaded string of amplifiers produce over and above the thermal noise?
Noise
What happens to the amount of noise generated by succeeding stages as the input signal and noise is amplified in cascaded amplifiers?
Adds relatively very little to the overall amount of noise
What is the significant effect of reactive circuits on noise in terms of frequency response?
Limitation on frequency response, affecting the effective bandwidth
What is the significant effect of reactive circuits on noise?
Limitation on frequency response
What does a reactive circuit's limitation on frequency response result in?
Effective or equivalent bandwidth
What is the effective noise bandwidth for a 3dB bandwidth of 500Hz determined by an RC circuit used in an amplifier system?
The effective noise bandwidth is determined by the 3dB bandwidth of 500Hz.
What is noise temperature and how is it related to thermal noise in devices?
Noise temperature is a measure of noise in a system due to thermal noise, which is directly proportional to temperature.
When is noise temperature most appropriate to use, and what does a lower noise temperature indicate?
Noise temperature is most appropriate for circuits operating at VHF, UHF, or microwave frequencies. A lower noise temperature indicates a better circuit, especially for low noise systems like masers and parametric preamplifiers.
What does SINAD stand for?
Signal plus Noise plus Distortion to Noise plus Distortion ratio
How is the SINAD ratio calculated?
SINAD = (Signal + Noise + Distortion power) / (Noise + Distortion power)
Why does the residual audio power exist in a communication system?
Due to the fact that amplifiers and other circuits in a receiver are not perfectly linear and introduce distortion
What form does the distortion take in a communication system?
The distortion takes the form of very low levels of signal harmonics
How do harmonics and noise affect the signal in a communication system?
Harmonics add to the signal along with the noise
What does SINAD ratio stand for in relation to signal quality in a communication system?
Signal-to-Noise-and-Distortion ratio
What is the role of the SINAD ratio in a communication system?
SINAD ratio makes no attempt to discriminate between or separate the noise and distortion signals
What is noise in the context of signal transmission?
Any unwanted or undesirable signal tending to interfere with the desired or wanted signal.
How can noise affect a signal in a medium?
Noise can affect the signal in the medium as there is no factor that can protect it when traveling aside from the type of modulation used before transmission.
What are the two categories of noise mentioned in the text?
1. Correlated Noise 2. Uncorrelated Noise
What is correlated noise?
Unwanted electrical energy present as a direct result of a signal, such as harmonic and intermodulation distortion.
Name the two types of correlated noise mentioned in the text.
a. Intermodulation Distortion b. Harmonic Distortion
Define uncorrelated noise.
Noise present regardless of whether there is a signal or not.
List the two types of uncorrelated noise discussed in the text.
a. External Noise b. Internal Noise
What is industrial man-made noise?
Noise produced by devices or equipment made by humans and affects frequencies up to 500MHz. Examples include combustion engines, fluorescent lamps, and switches.
What is static atmospheric noise?
Noise originating from lightning discharges during thunderstorms, rain, and dust storms. It has an inverse relationship with frequency and notably affects frequencies below 30 MHz.
What is space extraterrestrial noise?
Noise sourced from the sun, solar noise, stars, cosmic noise, and galaxies such as galactic noise. Observable between 8MHz to 143GHz.
Explain the 11-year noise cycle associated with solar noise.
The noise intensity produced by the sun varies with time, following an 11-year cycle. During its peak cycle, a tremendous amount of noise is produced.
What is combustion engine an example of?
Combustion engine is an example of a source of noise.
What is the frequency range affected by STATIC ATMOSPHERIC NOISE?
STATIC ATMOSPHERIC NOISE greatly affects frequencies below 30 MHz.
Where does SPACE EXTRA TERRESTRIAL NOISE come from?
SPACE EXTRA TERRESTRIAL NOISE comes from sources such as the sun, solar noise, stars, cosmic noise, and galaxies.
What is the frequency range observable for SPACE EXTRA TERRESTRIAL NOISE?
SPACE EXTRA TERRESTRIAL NOISE is observable between 8MHz to 143GHz.
What is the 11 year noise cycle related to SOLAR NOISE?
The 11 year noise cycle related to SOLAR NOISE is the varying noise intensity produced by the sun.
What disturbances in the ionosphere are caused by the sun during its peak cycle?
During its peak cycle, the sun causes disturbances in the ionosphere known as SIDs (Sudden Ionospheric Disturbances) due to solar flares and ionospheric storms.
What is the frequency range affected by COSMIC or GALACTIC NOISE?
COSMIC or GALACTIC NOISE affects the frequency range from 10MHz to 15GHz, but causes the greatest disruptions in the 15 to 150 MHz range.
Who is J.B. Johnson and why is noise related to him?
J.B. Johnson studied Johnson or Thermal or White Noise, which is noise coming from the rapid and random motion of charge carriers inside a resistive component when heated. It is also known as thermal noise.
What is internal noise also known as?
Johnson, thermal, white, or Gaussian noise
Who thoroughly studied Johnson noise in 1928?
J.B. Johnson
What is the major contribution of transistor noise due to shot effect?
Shot noise
Describe the nature of current carriers in all forms of semiconductors.
Current carriers have a discrete particle nature
What is pink noise also known as?
1f noise, flicker noise, excess noise, modulation noise
What is transit time noise and in which devices does it occur?
Noise that occurs in transistors due to the time it takes for a current carrier to move from input to output
What is resistance noise attributed to in transistors?
Internal resistance of the base, emitter, and collector
What is burst noise also known as and where is it observed?
Popcorn noise, observed in BJT transistors as bursts of two or more levels
What is the issue of noise in mixers compared to amplifiers?
Low transconductance and inadequate image frequency rejection
What is avalanche noise characterized by?
Large noise spikes due to collisions resulting in avalanche actions
What is partition noise characterized by?
Random fluctuations in the division of current in two or more electrodes
What is impulse noise composed of?
Irregular pulses or noise spikes of short duration and high amplitude, also known as HITS
Define signal-to-noise ratio.
A ratio used to measure the level of a desired signal compared to the level of background noise present
What is avalanche noise?
A large noise spikes due to collision that result in a valanching action
What is partition noise?
Random fluctuations in the division of current in two or more electrodes
What is impulse noise?
A non-continuous noise consisting of irregular pulses or noise spikes of short duration and relatively high amplitude
How is signal to noise ratio (SNR) usually expressed?
In power because the received signal is also expressed in terms of power
What are the units of measurement for inductance and capacitance in RF circuits?
Henries for inductance and Farads for capacitance
What is the quality (Q) of a component in RF circuits?
A measure of the energy stored to that which is lost in the component
What does R represent in an inductor in RF circuits?
Series resistance distributed along the windings
What does G represent in a capacitor in RF circuits?
Value of conductance through the dielectric between the capacitor plates
Define resonance in a circuit
Circuit condition where inductive and capacitive reactance are balanced (X L = X C )
What is the resonant frequency of a circuit and how is it expressed?
Frequency at which X L = X C ; expressed as f r
What is an RLC circuit and what components does it consist of?
Electrical circuit consisting of a resistor, inductor, and capacitor connected in series or parallel
What is the impedance of a series RLC circuit at its resonant frequency?
Minimum and equal to the value of the resistor (R)
Describe the impedance of a series RLC circuit at low and high frequencies
Low frequencies: high impedance due to high Xc; High frequencies: high impedance due to high X L
What happens to the impedance of a series RLC circuit at resonance (f = f r )?
Z = R, impedance is at its minimum value
What is an RLC circuit in series composed of?
A resistor, an inductor, and a capacitor connected in series
When is the impedance of a series RLC circuit minimum?
At its resonant frequency, where it is equal to the value of the resistor (R)
Why is the impedance of a series RLC circuit high at low frequencies?
Because the reactance of the capacitor (XC) is high at low frequencies
Why is the impedance of a series RLC circuit high at high frequencies?
Because the reactance of the inductor (XL) is high at high frequencies
What is the passband of a filter?
The band of frequencies that a filter allows to pass through without attenuation
What is the stopband of a filter?
The band of frequencies that a filter attenuates or blocks from passing through
What is the cutoff frequency of a filter?
The frequency at which the power output is reduced to 12 of the passband power, equivalent to a voltage or amplitude reduction to 707 of the passband
What is another term for the cutoff frequency of a filter?
Also known as the knee frequency, break frequency, or corner frequency
What is the cutoff frequency often referred to as in relation to the filter response?
The 3 dB point, as it is where the filter response drops down by 3 dB from the value of the passband response
What is the cutoff frequency (fc) in a filter response?
The frequency where the filter response drops down 3dB from the value of the passband response.
What does the cutoff frequency (fc) signify in terms of power output?
The frequency either above or below which the power output is reduced to 1/2 of the passband power (12 of passband power).
What is the significance of the cutoff frequency (fc) in terms of voltage or amplitude reduction?
Equivalent to a voltage or amplitude reduction to 0.707 of the passband.
What is another term used to refer to the cutoff frequency (fc)?
The 3 dB point, knee frequency, break frequency, or corner frequency.
What is the band of frequencies being rejected and a notch being cut into the output at the resonant frequency called?
Band reject or notch filter, sometimes referred to as a trap.
What is the resonant frequency (fr) for a circuit, and how is it determined?
The frequency at which a resonance occurs in the circuit. It can be determined by analyzing the circuit's components and characteristics.
What is the response curve seen in a bandpass filter configuration?
The response curve shows a peak response within a specific frequency range, known as the bandwidth of the filter.
What is the bandwidth (BW) of a filter
The frequency range between the high cutoff frequency (f hc) and low cutoff frequency (f lc).
What is the frequency range between f_lc and f_hc called in a bandpass filter?
Bandwidth (BW)
What does the quality factor Q of a filter measure?
Q provides a measure of how selective and narrow the passband of the filter is compared to its center frequency (fr).
As the quality factor Q of a filter increases, what happens to the filter's selectivity?
As Q increases, the filter becomes more selective, meaning a smaller passband and narrower bandwidth is allowed.
What is the limiting factor for the selectivity of a filter in terms of inductors?
The turns of wire and associated resistance used to make an inductor provide the limiting factor for the filter's selectivity.
What is a parallel LC circuit also known as?
A parallel LC circuit is sometimes called a tank circuit.
When is the resonant frequency of a parallel LC circuit reached in terms of the quality factor Q?
The transfer of energy between the inductor and capacitor in a parallel LC circuit occurs at a natural rate equal to the resonant frequency when Q is greater than 10 (Q>10).
What is a tank circuit also known as?
A parallel LC circuit
How is energy stored in a tank circuit?
Energy is stored in each reactive elements L and C, first in one then released to the other
At what rate does the transfer of energy between the two elements occur in a tank circuit?
At the resonant frequency
What is the form of the energy transfer between elements in a tank circuit?
Sinusoidal
What are the types of filters mentioned in the text?
1. Active filters 2. Passive filters
Define active filters
Filters that use an amplifier with passive elements to provide pass or reject characteristics
Define passive filters
Filters that contain only passive, non-amplifying components and provide pass or reject characteristics
What does an active device provide in terms of filters?
Voltage gain
What does a passive device provide in terms of filters?
Frequency selectivity
What is the definition of an octave in terms of frequency?
Change in frequency by a factor of 2
What is the definition of a decade in terms of frequency?
Change in frequency by a factor of 10
What is the roll-off rate in filters?
Rate of transition from passband to stopband or vice versa
List the categories of filters
1. Low pass 2. High pass 3. Band pass 4. Band stop
Describe a high pass filter
A filter that passes high frequencies well but attenuates or reduces frequencies lower than the cutoff frequency
Describe a low pass filter
A filter that passes low frequencies well but attenuates or reduces higher frequencies than the cutoff frequency
What is the roll off rate in the context of filters?
The rate of transition from passband to stopband or vice versa.
What is a band pass filter?
A filter that combines the properties of low pass and high pass filters to allow a specific range of frequencies to pass through.
What is a band stop filter also known as?
Band elimination, band reject, or notch filter.
What is a band stop filter?
Also known as a band elimination, band reject, or notch filter, this type of filter passes all frequencies above and below a particular range set by the component values.
How is the frequency response of a filter generally represented?
Using a Bode plot.
What is the rate of roll-off for an n order filter in terms of dB per octave?
6n dB per octave.
What is an oscillator in the context of communication systems?
A circuit capable of converting energy from DC into AC, capable of generating a repetitive waveform at a specified frequency.
What factors dictate the form of oscillator to be used in a given application?
Performance considerations, economic factors.
What forms of energy storage are mentioned in LC oscillators?
Capacitors and inductors store energy, with capacitors storing energy in the form of an electrostatic field.
What are the criteria used to determine the choice of oscillator type?
1. Output frequency required 2. Frequency stability required 3. Is the frequency to be variable and if so over what range 4. Allowable waveform distortion 5. Power output required
How does a capacitor store energy in an LC oscillator?
A capacitor stores energy in the form of an electrostatic field.
How does an inductor store energy in an LC oscillator?
An inductor uses a magnetic field to store energy.
Describe the process in an LC oscillator circuit involving a tank circuit and the flywheel effect.
When the capacitor is charged with a battery and the inductor is inserted into the circuit, the capacitor will discharge through the inductor. The inductor will create a magnetic field and then try to keep the current moving in the circuit, leading to an oscillation between the capacitor and inductor.
What happens once the capacitor discharges?
The inductor tries to keep the current moving by charging up the other plate of the capacitor
What happens when the inductor's field collapses?
The capacitor is recharged with the opposite polarity and discharges again through the inductor
What causes the oscillation in the circuit?
The interaction between the inductor and capacitor until the circuit runs out of energy due to resistance in the wire
What determines the frequency of oscillation in an LC tank circuit?
The size of the inductor and the capacitor
What is used to restore lost energy and provide a constant amplitude sine wave output in an LC oscillator?
An amplifier
What is the resulting waveform in an LC oscillator known as?
Continuous wave (CW)
What are LC oscillators essentially in terms of circuitry?
Feedback amplifiers with the feedback helping to increase or sustain the self-generated output
What are the criteria for oscillation stated by the Barkhausen criteria?
1. The loop gain must be 1 (unity) 2. The loop phase shift must be n * 360 degrees, where n is any integer
What type of oscillators are crystal oscillators?
Oscillators utilizing crystals, most commonly quartz
Describe the ideal oscillator circuit according to the Barkhausen criteria.
The ideal oscillator circuit has a loop gain initially greater than 1 when signals are small, decreasing to 1 as the signal reaches the desired amplitude.
What are the types of oscillator circuits?
1. Hartley Oscillators. 2. Colpitts Oscillators. 3. Clapp Oscillators. 4. Crystal Oscillators.
How do crystal oscillators work based on the text?
A crystal oscillator circuit amplifies a voltage signal from a quartz resonator and feeds it back to the resonator, sustaining oscillation. The quartz crystal behaves like a circuit composed of an inductor, capacitor, and resistor with a precise resonant frequency.
What is the electrical equivalent circuit of a quartz crystal?
Inductor, capacitor, and resistor with a precise resonant frequency
How does a crystal oscillator circuit sustain oscillation?
By taking a voltage signal from the quartz resonator, amplifying it, and feeding it back to the resonator
What determines the resonant frequency of a crystal oscillator circuit?
The rate of expansion and contraction of the quartz, determined by the cut and size of the crystal
What is modulation?
Mixing of low frequency signals (modulating signal) with high frequency signals (carrier signal), where some characteristic of a high frequency sine wave is varied in accordance with the instantaneous value of the signal. It is the imposition of information on a given signal or the modification of one signal by another signal.
What are the 3 types of modulation according to the carrier used?
Continuous Wave-carrier is a sinusoid Pulse - carrier is a train of pulses (discrete)
What are the 2 types of modulation according to the method used?
Analog modulation, Digital modulation
What are 5 reasons for modulation?
1. To reduce antenna lengths. 2. To reduce noise interference. 3. For frequency assignments. 4. For multiplexing. 5. To overcome equipment limitations.
What is analog modulation?
Analog modulation includes techniques like Amplitude Modulation (AM).
What is phase modulation?
Modulating the phase of a carrier signal to transmit information.
What is angle modulation?
A term that refers to both phase modulation and frequency modulation.
What is frequency modulation?
Modulating the frequency of a carrier signal to transmit information.
What is digital modulation?
Modulating digital signals to transmit information through a carrier signal.
What is pulse code modulation?
A method for converting analog signals to digital signals for transmission.
What is delta modulation?
A form of modulation where the difference between consecutive signal samples is transmitted.
What is the relationship between instantaneous amplitude and peak amplitude in a sinusoidal signal?
Instantaneous amplitude can vary but peak amplitude remains constant.
What does 't' represent in a sinusoidal signal?
Instantaneous time or time variable in the signal.
What does 'f' represent in a sinusoidal signal?
Angular frequency or frequency of the signal.
Explain the concept of modulation.
Modulation is the process of encoding information from voice, video, or digital signals onto a carrier signal.
What happens in amplitude modulation (AM)?
The information signal modulates the amplitude of the carrier sine wave.
What does the envelope of a carrier waveform connect in amplitude modulation?
Connects the positive and negative peaks of the carrier waveform.
What is the purpose of modulating a carrier signal?
To transmit information effectively by varying certain characteristics of the carrier signal.
What is Amplitude Modulation (AM)?
Amplitude Modulation (AM) is a modulation technique in which the amplitude of a carrier wave is varied in proportion to the waveform of the modulating signal.
What is the modulation index (m) in AM?
The modulation index (m) in AM is a value that describes the relationship between the amplitude of the modulating signal and the amplitude of the carrier signal. It is also known as the modulating factor, coefficient, degree of modulation, or depth of modulation.
What does the modulation index describe in AM?
The relationship between the amplitude of the modulating signal and the amplitude of the carrier signal.
What are some other names for the modulation index?
Modulating factor, coefficient, degree of modulation, depth of modulation.
What is the range of values for the modulation index in AM?
0 to 1.
What are side frequencies or sidebands generated as part of the modulation process?
Side frequencies or sidebands are generated as part of the modulation process and occur in the frequency spectrum directly above and below the carrier frequency.
How many sidebands are generated by a single frequency sine wave modulation?
Single frequency sine wave modulation generates TWO sidebands.
What type of wave generates a range of sidebands in modulation?
Complex wave (e.g., voice or video modulation) generates a range of sidebands.
What is the AM wave in modulation?
The AM wave is the algebraic sum of the carrier and upper and lower sideband sine waves.
What is the relationship between the time and frequency domains in modulation?
The relationship between the time and frequency domains in modulation is determined by the modulation index. The higher the modulation index, the higher the output power.
What is the criterion for determining whether a signal is overmodulated?
To determine if a signal is overmodulated, compare the peak value of the modulated wave to the carrier wave peak value. If it exceeds 1, the signal is overmodulated.
What is the relationship between modulation index and output power in an AM signal?
Higher the modulation index, higher the output power.
What are the sideband frequencies and total bandwidth for an AM broadcast station transmitting modulating frequencies up to 5 kHz on a frequency of 980 kHz?
Sideband frequencies: 975 kHz and 985 kHz, Total bandwidth: 10 kHz
Define simultaneous modulation.
Modulation by several carriers
What is the bandwidth formula for Amplitude Modulation (AM)?
BW = 2 x fm
What important notes are highlighted in key points regarding modulation?
a) Information is present only in the sidebands. b) During 100% modulation, 2/3 of the total power is wasted in the carrier, with the carrier power percentage being 66-67% of the transmitted AM. c) Information on the LSB is essential in modulation.
What is angle modulation used for?
Angle modulation is used for radio broadcasting, sound signal in TV, two-way fixed and mobile radio systems, cellular telephone systems, and satellite communications.
What is Phase Modulation (PM)?
Phase Modulation (PM) is a modulation wherein the phase of the carrier is made proportional to the instantaneous value of the modulating signal.
What is Carrier or Frequency deviation (f_d) in Phase Modulation?
Carrier or Frequency deviation (f_d) is the amount of change in carrier frequency produced by the modulating signal. The frequency deviation rate is how many times per second the carrier frequency deviates above or below its center frequency.
When does a frequency shift occur in Phase Modulation (PM)?
A frequency shift occurs in Phase Modulation (PM) only when the modulating signal amplitude varies.
What is the relationship between the Modulating Signal and Carrier Deviation in Phase Modulation (PM)?
In Phase Modulation (PM), the carrier deviation is proportional to both the modulating frequency and the amplitude. The frequency deviation is directly proportional to the amplitude of the modulating signal.
What is the relationship between frequency deviation and the amplitude of the modulating signal in PM?
Directly proportional
What factors affect the carrier deviation in PM?
Modulating frequency and amplitude
Type of angle modulation where carrier frequency is varied relative to modulating frequency signal
Frequency modulation (FM)
What is the relationship between the peak voltage of the carrier signal (c) and the modulation index (m) in frequency modulation (FM)?
The modulation index (m) is 2 times the frequency of the peak voltage of the carrier signal (c).
What happens to the carrier frequency in FM as the modulating signal amplitude increases?
When the modulating signal amplitude increases, the carrier frequency also increases in FM.
Explain the behavior of the carrier in FM with no modulation.
In FM, with no modulation, the carrier is at its normal center or resting frequency. The carrier amplitude remains constant in FM while the carrier frequency is changed by the modulating signal.
What is Frequency Deviation?
The amount of change in carrier frequency produced by modulating signal.
Where does the maximum frequency deviation occur in FM modulation?
At the maximum amplitude of the modulating signal.
What is Carrier Swing (CS) in FM modulation?
The total variation in frequency of the carrier.
What is Modulation Index in FM signals?
The modulation index determines the number of significant sidebands in an FM signal. It is directly proportional to the modulating voltage and inversely proportional to the modulating signal frequency.
What is Deviation Ratio in FM modulation?
The ratio of the maximum permissible frequency deviation to the maximum permissible modulating frequency.
What are the main differences between Wideband FM and Narrowband FM?
Wideband FM is used for FM broadcast, entertainment, and mobile communications with higher modulation indices and maximum deviations, while Narrowband FM is used for voice transmissions with lower modulation indices and maximum deviations.
What are the practical limits to the modulation index and frequency deviation in FM signals?
There are no theoretical limits, but practical limits are set by a compromise between signal-to-noise ratio and bandwidth. Government regulations also limit the bandwidth in terms of maximum frequency deviation and the maximum modulation frequency.
What does the modulation index 'm' represent in FM broadcasting?
The modulation index represents the ratio of the frequency deviation to the modulating frequency in FM broadcasting.
What are the typical values for modulation index 'm' in FM broadcasting?
The typical values for modulation index 'm' in FM broadcasting range from 5 to 2500.
What is Narrowband FM (NBFM) used for in FM broadcasting?
Narrowband FM (NBFM) is used for voice transmissions in FM broadcasting.
What is Wideband FM (WBFM) used for?
WBFM is used for most applications except for voice transmissions, with higher modulation indices and maximum deviations.
What complex mathematical process is used to solve the equation that expresses the phase angle in terms of the sine wave modulating signal in FM?
Bessel functions
What is the name of the coefficients widely available for solving the equation using Bessel functions in FM?
Bessel coefficients
How does the bandwidth of an FM signal change with higher modulation index?
It increases, resulting in a greater number of significant sidebands and wider signal bandwidth.
How can the bandwidth of an FM signal be restricted when spectrum conservation is necessary?
By putting an upper limit on the modulation index
What function is used to illustrate the corresponding frequency spectrum of an FM wave in this problem?
Bessel function is used to illustrate the corresponding frequency spectrum of an FM wave.
What is the relationship between transmitted power and depth of modulation in FM?
In FM, the total transmitted power remains constant but with increased depth of modulation, the required bandwidth is increased.
What are the components in the block diagram of an FM transmitter?
RF oscillator - Exciter (providing an FM RF signal) - Power amplifier and connected below the exciter we have - Pre-emphasis network-Audio amplifier
What is pre-emphasis in the context of FM transmission?
Pre-emphasis is the boosting of the higher modulating frequencies at the transmitter to improve noise immunity at FM and prevent degradation of the higher frequency components of the transmitted intelligence.
What is de-emphasis in FM receivers and what is the time constant for the pre-emphasis and de-emphasis networks?
De-emphasis is reducing the amplitude of higher modulating frequencies at the receiver. The time constant for both pre-emphasis and de-emphasis networks is 75 us (or 150 us for Europe, 25 us for Dolby) with a cutoff frequency of 2122 Hz.
What is the Image Frequency effect in FM?
Effect of two stations being received simultaneously
What is Co-channel Interference in FM?
Interference true to mobile receivers when travelling from one transmitter toward another, minimized by capture effect
How does FM minimize interference from undesired signals and noise?
By capturing the strongest signal or station and minimizing other signals operating on the same frequency
What is Adjacent Channel Interference in FM?
Interference created between tuning two adjacent stations due to imperfections in filter circuits
What is the Stereophonic FM Multiplex System?
A 1961 modulation system in which left and right channels are transmitted simultaneously and independently
What are the different types of FM demodulators?
Slope Detector, Pulse Averaging Discriminators, Quadrature Detector, Phase Locked Loops, Foster Seeley Discriminator
What is the Indirect Method for FM demodulation known as?
FM Armstrong Method
How is Wideband FM obtained in the FM Armstrong Method?
By successive frequency multiplication of the output from a balanced modulator and a crystal that is shifted 90 degrees
What are the various types of demodulators for FM signals?
1. Slope Detector 2. Pulse Averaging Discriminators 3. Quadrature Detector 4. Phase Locked Loops 5. Foster Seeley Discriminator
What are the methods used in FM demodulation?
1. Indirect Method 2. Armstrong Method
How is the modulating signal modulated before FM demodulation?
It is modulated using a balanced modulator.
What device is used in combination with the modulated signal in FM demodulation to obtain Wideband FM?
Crystal oscillator
What is the process to obtain Wideband FM in FM demodulation?
Successive frequency multiplication of the output
What components are involved in the process of FM demodulation for Wideband FM?
Crystal oscillator, Buffer, Phase shifter, Combining network, Balanced Modulator
What are the characteristics of FM waves in terms of carrier frequency (f c) and modulation frequency (m f)?
1. Low f c and m f - Carrier only 2. Medium f c and low m f - Low sidebands 3. High f c and m f - High sidebands
What type of modulation involves shifting the carrier frequency (f c) by 90 degrees?
Armstrong Modulation
What is the carrier swing when the oscillator deviates 2kHz in an FM transmitter with two doublers and one tripler?
d) 48kHz
What principle do FM receivers utilize?
Superheterodyne principle
What frequency range do FM receivers operate in?
88-108 MHz
What is used in FM receivers to ensure the received signal is constant in amplitude before it enters the discriminator or detector?
Limiter
What causes interference in the form of noise in FM signals?
Lightning, motors, automotive ignition systems, power line switching
What is the role of limiter circuits in FM receivers in terms of amplitude of the received signal?
Limiter circuits restrict the amplitude of the received signal
How does FM offer noise immunity compared to AM signals?
FM has superior immunity to noise due to clipper limiter circuits in the receiver
What effect helps FM signals reject interfering signals on the same frequency?
Capture effect
What is the purpose of limiter circuits in an FM signal?
To clip amplitude variations and preserve the frequency variations of the carrier signal.
How does amplitude clipping in FM signals affect the information content?
It does not affect the information content as it is contained within the frequency variations of the carrier signal.
What is the noise suppression effect of FM signals?
FM signals have superior noise immunity due to clipper limiter circuits in the receiver.
Explain the capture effect in FM signals.
The capture effect in FM signals refers to the rejection of interfering signals on the same frequency.
What is a benefit of FM signals over AM signals in terms of power efficiency?
FM signals do not require linear amplifiers to increase power levels, leading to increased transmitter efficiency.
What are some disadvantages of FM?
FM uses considerably more frequency spectrum space and has used more complex circuitry for modulation and demodulation.
What has happened with the complex circuitry used in FM with the proliferation of ICs?
With the proliferation of ICs, the complex circuitry used in FM has all but disappeared as ICs are inexpensive and easy to use.
What are the major applications of AM and FM?
The major applications of AM and FM include electronic communication.
What is the significance of human communication?
Communication is the process of exchanging information, with main barriers being language and distance. Contemporary society emphasizes the accumulation, packaging, and exchange of information.
What are some methods of communication?
Face to face, signals, written word (letters), and electrical innovations such as telegraph, telephone, radio, television, internet, and computer.
Untitled Flashcards
Study
What is a decibel?
A unit used in electrical engineering and acoustics to express on a logarithmic scale the ratio between two values with the same dimensions.
What are the quantities compared using decibels?
Two voltages, two power levels, two sound pressure levels, and so on.
What are the three factors that affect the extent of damage to hearing caused by noise?
1. Decibel level (how loud the sound is) 2. Distance (how close you are to the source of the sound) 3. Time (the length of time you are exposed to the sound)
How is sound measured?
Sound is measured in units called decibels (dB).
What is the significance of A-weighted decibels (dBA)?
A weighted decibels can be used to describe sound based on what human ears can actually hear, as people can't hear all frequencies or pitches of sound.
What decibel level is generally considered safe for sounds?
Sounds at or below 70 dBA are generally considered safe.
At what decibel level is sound more likely to damage hearing over time?
Any sound at or above 85 dBA is more likely to damage hearing over time.
What is the increased risk for hearing loss associated with noise levels of 85 dBA or higher?
People exposed to such noise levels over long periods are at a much greater risk for hearing loss.
Why are some workers required to wear hearing protectors like earplugs or earmuffs?
To protect their hearing from noise levels at or above 85 dBA while they are on the job.
What decibel level is generally considered safe for human ears?
Sounds at or below 70 dBA
At what decibel level are sounds more likely to damage hearing over time?
Any sound at or above 85 dBA
What is the risk for hearing loss for people exposed to noise levels at 85 dBA or higher over long periods of time?
Much greater risk
Why are some workers required to wear hearing protectors like earplugs or earmuffs on the job?
To protect their hearing from exposure to high decibel levels
What are some factors that affect hearing loss?
Decibel level, distance, and time
What is the decibel level of many devices that children use today?
Higher than 85 dBA
How intense is 110 dBA compared to 85 decibels?
More than 100 times as intense
Are manufacturers required to limit the maximum sound output of music devices?
No, they are not required to do so
What can volume limiting controls on devices help with?
Setting the maximum volume to a safe level
How does the sound level change as you move closer or further away from the source?
It gets louder as you move closer and softer as you move away
In what situation at a concert can reduce the risk of hearing damage?
Sitting away from the speakers
What impact does exposure to loud sounds on a regular basis have on the risk of hearing damage?
It increases the risk for permanent damage over time
What is considered safe sound levels that last a long time?
Sounds at or below 70 dBA
At what decibel level and duration is it more likely for noises to damage hearing?
85 dBA lasting a few hours, 100 dBA lasting at least 14 minutes, 110 dBA lasting at least 2 minutes
Why is decibel notation mainly used in calculating signal levels?
It is convenient for calculating signal levels
What is the risk of permanent damage to hearing if exposed to loud sounds on a regular basis?
Increases over time
What is the potential effect of a single but long-lasting loud event on hearing?
Can cause damage
What is the considered safe level for sounds that last a long time?
70 dBA or below
At what sound level and duration are noises more likely to damage hearing?
85 dBA for a few hours, 100 dBA for at least 14 minutes, 110 dBA for at least 2 minutes
What is the main reason for using decibel notation in calculating signal levels?
Convenience
When working with decibel values, what operation can be performed with dB values?
Decibel values can only be added or subtracted
How could the operation of adding individual gains of two amplifiers in cascade be interpreted in terms of dB?
It could be interpreted as adding the individual dB gains to get the overall gain of the combination
How could the operation of getting the net gain of an amplifier and a lossy section be interpreted in terms of dB?
It could be interpreted as subtracting the dB loss from the dB gain to get the net gain
What is correlated noise?
Unwanted electrical energy that interferes with the desired signal
What is correlated noise?
Unwanted electrical energy that is used before it is transmitted, and falls into two categories.
What are the two categories of noise?
1. Correlated noise 2. Uncorrelated noise
What is noise in the context of signal transmission?
Any unwanted or undesirable signal that interferes with the desired signal.
How can noise affect a signal in the medium?
Noise can affect the signal in the medium as there is no factor to protect the signal except for the type of modulation used before transmission.
What are the two categories of noise?
1. Correlated Noise 2. Uncorrelated Noise
What is correlated noise?
Unwanted electrical energy present as a direct result of a signal, such as harmonic and intermodulation distortion.
What are the two types of correlated noise?
a. Intermodulation Distortion b. Harmonic Distortion
What is uncorrelated noise?
Noise present regardless of whether there is a signal or not.
What are the two types of uncorrelated noise?
a. External Noise b. Internal Noise
What is external noise?
Noise produced by devices or equipment made by humans that affects frequencies up to 500MHz.
What are the sources of external noise?
1. Industrial Man-Made Noise 2. Static Atmospheric Noise 3. Space (Extra Terrestrial) Noise
What is industrial man-made noise?
Noise produced by devices or equipment made by humans, affecting frequencies up to 500MHz. Example sources are combustion engines, fluorescent lamps, switches, etc.
What is static atmospheric noise?
Noise coming from lightning discharges during thunderstorms, rain, and dust storms. It greatly affects frequencies below 30MHz.
What is space (extra-terrestrial) noise?
Noise coming from sources like the sun, solar noise, stars, cosmic noise, and galaxies. It is observable between 8MHz to 143GHz.
What is solar noise?
The noise intensity produced by the sun, varying with time and having a repeating 11-year cycle. During its peak cycle, a tremendous amount of noise is produced.
How is solar noise intensity affected by the sun's activity?
Solar noise intensity varies with time and has a repeating 11-year cycle, with a peak cycle producing a significant amount of noise.
What are some examples of sources of electromagnetic noise in the environment?
Combustion engines, fluorescent lamps, switches, etc.
What is static atmospheric noise and when does it greatly affect frequencies?
Static atmospheric noise is noise coming from lightning discharges during thunderstorms and rain/dust storms. It greatly affects frequencies below 30 MHz.
What is space or extraterrestrial noise and what are some sources of it?
Space or extraterrestrial noise is noise coming from the sun, solar noise, stars, cosmic noise, and galaxies. Sources include sun, stars, cosmic noise, and galaxies.
What is solar noise and how does it affect radio signal interference during its peak cycle?
Solar noise is the noise intensity produced by the sun, which varies with time in a repeating 11-year cycle. During its peak cycle, a tremendous amount of noise is produced causing radio signal interference and making many frequencies unusable for communications.
What is cosmic noise and what frequency range does it affect the most?
Cosmic noise is noise coming from stars and affects the frequency range from 10 MHz to 15 GHz, with the greatest disruptions in the 15 to 150 MHz range. Sources include Cassiopeia A and Cygnus A.
What is internal noise and what are some names it is known by?
Internal noise is noise coming from the rapid and random motion of charge carriers inside a resistive component when heated. It is also known as Johnson noise, thermal noise, white noise, or Gaussian noise.
What is the frequency range affected by stars and cosmic sources in terms of EMF interference?
10MHz to 15GHz, with the greatest disruptions in the 15 to 150 MHz range
What are two of the strongest sources of EMF interference from stars.
Cassiopeia A and Cygnus A
What is Johnson noise, and why is it also known as thermal noise?
Noise from rapid and random motion of charge carriers in a resistive component when heated; named after J.B. Johnson and is temperature dependent
Shot Noise Definition:
Shot noise is the major contribution of transistor noise due to shot effect. Current carriers in semiconductors have a discrete particle nature.
What is the major contribution of transistor noise due to shot effect?
Shot noise
What type of noise is also known as 1f noise, flicker noise, excess noise, or modulation noise found in transistors?
PINK NOISE
What is transit time noise and where does it occur?
Transit time noise is a kind of noise that occurs in transistors. Transit time refers to the duration of time it takes for a current carrier like a hole or electron to move from input to output. The effect of this noise can be seen in high-frequency operation.
What is resistance noise and what are its contributors?
Resistance noise is due to the base, emitter, and collector internal resistance of a transistor.
What is burst noise, and where is it observed in transistors?
Burst noise, also known as popcorn noise, is a low-frequency noise observed in BJT (Bipolar Junction Transistor) that appears as a series of bursts of two or more levels.
What is avalanche noise and what causes it?
Avalanche noise is large noise spikes due to collisions that result in an avalanche action in a device.
What is partition noise?
Partition noise refers to random fluctuations in the division of current in two or more electrodes.
What is impulse noise characterized by?
Impulse noise is non-continuous, consisting of irregular pulses or noise spikes of short duration and relatively high amplitude. The spikes are called HITS (High Impulse Transient Signals).
What is avalanche noise?
Large noise spikes due to collisions that result in a valanching action.
What is partition noise?
Random fluctuations in the division of current in two or more electrodes.
What is impulse noise?
A non-continuous noise consisting of irregular pulses or noise spikes of short duration and relatively high amplitude.
What is the Signal-to-Noise Ratio (SNR) usually expressed in?
Power, because the received signal is also expressed in terms of power.
What is Noise Factor (NF), Noise Ratio (NR), and Noise Figure (F) related to?
They are related to the signal-to-noise ratio.
What is used to specify how noisy a device is in terms of noise figure?
Noise Figure
What is used to identify the noise content at a specific point but is not useful in relating how much additional noise a device has injected into a signal going from input to output?
Signal-to-Noise Ratio (SNR)
What do each amplifier in a cascaded string of amplifiers produce over and above the thermal noise?
Noise
What happens to the amount of noise generated by succeeding stages as the input signal and noise is amplified in cascaded amplifiers?
Adds relatively very little to the overall amount of noise
What is the significant effect of reactive circuits on noise in terms of frequency response?
Limitation on frequency response, affecting the effective bandwidth
What is the significant effect of reactive circuits on noise?
Limitation on frequency response
What does a reactive circuit's limitation on frequency response result in?
Effective or equivalent bandwidth
What is the effective noise bandwidth for a 3dB bandwidth of 500Hz determined by an RC circuit used in an amplifier system?
The effective noise bandwidth is determined by the 3dB bandwidth of 500Hz.
What is noise temperature and how is it related to thermal noise in devices?
Noise temperature is a measure of noise in a system due to thermal noise, which is directly proportional to temperature.
When is noise temperature most appropriate to use, and what does a lower noise temperature indicate?
Noise temperature is most appropriate for circuits operating at VHF, UHF, or microwave frequencies. A lower noise temperature indicates a better circuit, especially for low noise systems like masers and parametric preamplifiers.
What does SINAD stand for?
Signal plus Noise plus Distortion to Noise plus Distortion ratio
How is the SINAD ratio calculated?
SINAD = (Signal + Noise + Distortion power) / (Noise + Distortion power)
Why does the residual audio power exist in a communication system?
Due to the fact that amplifiers and other circuits in a receiver are not perfectly linear and introduce distortion
What form does the distortion take in a communication system?
The distortion takes the form of very low levels of signal harmonics
How do harmonics and noise affect the signal in a communication system?
Harmonics add to the signal along with the noise
What does SINAD ratio stand for in relation to signal quality in a communication system?
Signal-to-Noise-and-Distortion ratio
What is the role of the SINAD ratio in a communication system?
SINAD ratio makes no attempt to discriminate between or separate the noise and distortion signals
What is noise in the context of signal transmission?
Any unwanted or undesirable signal tending to interfere with the desired or wanted signal.
How can noise affect a signal in a medium?
Noise can affect the signal in the medium as there is no factor that can protect it when traveling aside from the type of modulation used before transmission.
What are the two categories of noise mentioned in the text?
1. Correlated Noise 2. Uncorrelated Noise
What is correlated noise?
Unwanted electrical energy present as a direct result of a signal, such as harmonic and intermodulation distortion.
Name the two types of correlated noise mentioned in the text.
a. Intermodulation Distortion b. Harmonic Distortion
Define uncorrelated noise.
Noise present regardless of whether there is a signal or not.
List the two types of uncorrelated noise discussed in the text.
a. External Noise b. Internal Noise
What is industrial man-made noise?
Noise produced by devices or equipment made by humans and affects frequencies up to 500MHz. Examples include combustion engines, fluorescent lamps, and switches.
What is static atmospheric noise?
Noise originating from lightning discharges during thunderstorms, rain, and dust storms. It has an inverse relationship with frequency and notably affects frequencies below 30 MHz.
What is space extraterrestrial noise?
Noise sourced from the sun, solar noise, stars, cosmic noise, and galaxies such as galactic noise. Observable between 8MHz to 143GHz.
Explain the 11-year noise cycle associated with solar noise.
The noise intensity produced by the sun varies with time, following an 11-year cycle. During its peak cycle, a tremendous amount of noise is produced.
What is combustion engine an example of?
Combustion engine is an example of a source of noise.
What is the frequency range affected by STATIC ATMOSPHERIC NOISE?
STATIC ATMOSPHERIC NOISE greatly affects frequencies below 30 MHz.
Where does SPACE EXTRA TERRESTRIAL NOISE come from?
SPACE EXTRA TERRESTRIAL NOISE comes from sources such as the sun, solar noise, stars, cosmic noise, and galaxies.
What is the frequency range observable for SPACE EXTRA TERRESTRIAL NOISE?
SPACE EXTRA TERRESTRIAL NOISE is observable between 8MHz to 143GHz.
What is the 11 year noise cycle related to SOLAR NOISE?
The 11 year noise cycle related to SOLAR NOISE is the varying noise intensity produced by the sun.
What disturbances in the ionosphere are caused by the sun during its peak cycle?
During its peak cycle, the sun causes disturbances in the ionosphere known as SIDs (Sudden Ionospheric Disturbances) due to solar flares and ionospheric storms.
What is the frequency range affected by COSMIC or GALACTIC NOISE?
COSMIC or GALACTIC NOISE affects the frequency range from 10MHz to 15GHz, but causes the greatest disruptions in the 15 to 150 MHz range.
Who is J.B. Johnson and why is noise related to him?
J.B. Johnson studied Johnson or Thermal or White Noise, which is noise coming from the rapid and random motion of charge carriers inside a resistive component when heated. It is also known as thermal noise.
What is internal noise also known as?
Johnson, thermal, white, or Gaussian noise
Who thoroughly studied Johnson noise in 1928?
J.B. Johnson
What is the major contribution of transistor noise due to shot effect?
Shot noise
Describe the nature of current carriers in all forms of semiconductors.
Current carriers have a discrete particle nature
What is pink noise also known as?
1f noise, flicker noise, excess noise, modulation noise
What is transit time noise and in which devices does it occur?
Noise that occurs in transistors due to the time it takes for a current carrier to move from input to output
What is resistance noise attributed to in transistors?
Internal resistance of the base, emitter, and collector
What is burst noise also known as and where is it observed?
Popcorn noise, observed in BJT transistors as bursts of two or more levels
What is the issue of noise in mixers compared to amplifiers?
Low transconductance and inadequate image frequency rejection
What is avalanche noise characterized by?
Large noise spikes due to collisions resulting in avalanche actions
What is partition noise characterized by?
Random fluctuations in the division of current in two or more electrodes
What is impulse noise composed of?
Irregular pulses or noise spikes of short duration and high amplitude, also known as HITS
Define signal-to-noise ratio.
A ratio used to measure the level of a desired signal compared to the level of background noise present
What is avalanche noise?
A large noise spikes due to collision that result in a valanching action
What is partition noise?
Random fluctuations in the division of current in two or more electrodes
What is impulse noise?
A non-continuous noise consisting of irregular pulses or noise spikes of short duration and relatively high amplitude
How is signal to noise ratio (SNR) usually expressed?
In power because the received signal is also expressed in terms of power
What are the units of measurement for inductance and capacitance in RF circuits?
Henries for inductance and Farads for capacitance
What is the quality (Q) of a component in RF circuits?
A measure of the energy stored to that which is lost in the component
What does R represent in an inductor in RF circuits?
Series resistance distributed along the windings
What does G represent in a capacitor in RF circuits?
Value of conductance through the dielectric between the capacitor plates
Define resonance in a circuit
Circuit condition where inductive and capacitive reactance are balanced (X L = X C )
What is the resonant frequency of a circuit and how is it expressed?
Frequency at which X L = X C ; expressed as f r
What is an RLC circuit and what components does it consist of?
Electrical circuit consisting of a resistor, inductor, and capacitor connected in series or parallel
What is the impedance of a series RLC circuit at its resonant frequency?
Minimum and equal to the value of the resistor (R)
Describe the impedance of a series RLC circuit at low and high frequencies
Low frequencies: high impedance due to high Xc; High frequencies: high impedance due to high X L
What happens to the impedance of a series RLC circuit at resonance (f = f r )?
Z = R, impedance is at its minimum value
What is an RLC circuit in series composed of?
A resistor, an inductor, and a capacitor connected in series
When is the impedance of a series RLC circuit minimum?
At its resonant frequency, where it is equal to the value of the resistor (R)
Why is the impedance of a series RLC circuit high at low frequencies?
Because the reactance of the capacitor (XC) is high at low frequencies
Why is the impedance of a series RLC circuit high at high frequencies?
Because the reactance of the inductor (XL) is high at high frequencies
What is the passband of a filter?
The band of frequencies that a filter allows to pass through without attenuation
What is the stopband of a filter?
The band of frequencies that a filter attenuates or blocks from passing through
What is the cutoff frequency of a filter?
The frequency at which the power output is reduced to 12 of the passband power, equivalent to a voltage or amplitude reduction to 707 of the passband
What is another term for the cutoff frequency of a filter?
Also known as the knee frequency, break frequency, or corner frequency
What is the cutoff frequency often referred to as in relation to the filter response?
The 3 dB point, as it is where the filter response drops down by 3 dB from the value of the passband response
What is the cutoff frequency (fc) in a filter response?
The frequency where the filter response drops down 3dB from the value of the passband response.
What does the cutoff frequency (fc) signify in terms of power output?
The frequency either above or below which the power output is reduced to 1/2 of the passband power (12 of passband power).
What is the significance of the cutoff frequency (fc) in terms of voltage or amplitude reduction?
Equivalent to a voltage or amplitude reduction to 0.707 of the passband.
What is another term used to refer to the cutoff frequency (fc)?
The 3 dB point, knee frequency, break frequency, or corner frequency.
What is the band of frequencies being rejected and a notch being cut into the output at the resonant frequency called?
Band reject or notch filter, sometimes referred to as a trap.
What is the resonant frequency (fr) for a circuit, and how is it determined?
The frequency at which a resonance occurs in the circuit. It can be determined by analyzing the circuit's components and characteristics.
What is the response curve seen in a bandpass filter configuration?
The response curve shows a peak response within a specific frequency range, known as the bandwidth of the filter.
What is the bandwidth (BW) of a filter
The frequency range between the high cutoff frequency (f hc) and low cutoff frequency (f lc).
What is the frequency range between f_lc and f_hc called in a bandpass filter?
Bandwidth (BW)
What does the quality factor Q of a filter measure?
Q provides a measure of how selective and narrow the passband of the filter is compared to its center frequency (fr).
As the quality factor Q of a filter increases, what happens to the filter's selectivity?
As Q increases, the filter becomes more selective, meaning a smaller passband and narrower bandwidth is allowed.
What is the limiting factor for the selectivity of a filter in terms of inductors?
The turns of wire and associated resistance used to make an inductor provide the limiting factor for the filter's selectivity.
What is a parallel LC circuit also known as?
A parallel LC circuit is sometimes called a tank circuit.
When is the resonant frequency of a parallel LC circuit reached in terms of the quality factor Q?
The transfer of energy between the inductor and capacitor in a parallel LC circuit occurs at a natural rate equal to the resonant frequency when Q is greater than 10 (Q>10).
What is a tank circuit also known as?
A parallel LC circuit
How is energy stored in a tank circuit?
Energy is stored in each reactive elements L and C, first in one then released to the other
At what rate does the transfer of energy between the two elements occur in a tank circuit?
At the resonant frequency
What is the form of the energy transfer between elements in a tank circuit?
Sinusoidal
What are the types of filters mentioned in the text?
1. Active filters 2. Passive filters
Define active filters
Filters that use an amplifier with passive elements to provide pass or reject characteristics
Define passive filters
Filters that contain only passive, non-amplifying components and provide pass or reject characteristics
What does an active device provide in terms of filters?
Voltage gain
What does a passive device provide in terms of filters?
Frequency selectivity
What is the definition of an octave in terms of frequency?
Change in frequency by a factor of 2
What is the definition of a decade in terms of frequency?
Change in frequency by a factor of 10
What is the roll-off rate in filters?
Rate of transition from passband to stopband or vice versa
List the categories of filters
1. Low pass 2. High pass 3. Band pass 4. Band stop
Describe a high pass filter
A filter that passes high frequencies well but attenuates or reduces frequencies lower than the cutoff frequency
Describe a low pass filter
A filter that passes low frequencies well but attenuates or reduces higher frequencies than the cutoff frequency
What is the roll off rate in the context of filters?
The rate of transition from passband to stopband or vice versa.
What is a band pass filter?
A filter that combines the properties of low pass and high pass filters to allow a specific range of frequencies to pass through.
What is a band stop filter also known as?
Band elimination, band reject, or notch filter.
What is a band stop filter?
Also known as a band elimination, band reject, or notch filter, this type of filter passes all frequencies above and below a particular range set by the component values.
How is the frequency response of a filter generally represented?
Using a Bode plot.
What is the rate of roll-off for an n order filter in terms of dB per octave?
6n dB per octave.
What is an oscillator in the context of communication systems?
A circuit capable of converting energy from DC into AC, capable of generating a repetitive waveform at a specified frequency.
What factors dictate the form of oscillator to be used in a given application?
Performance considerations, economic factors.
What forms of energy storage are mentioned in LC oscillators?
Capacitors and inductors store energy, with capacitors storing energy in the form of an electrostatic field.
What are the criteria used to determine the choice of oscillator type?
1. Output frequency required 2. Frequency stability required 3. Is the frequency to be variable and if so over what range 4. Allowable waveform distortion 5. Power output required
How does a capacitor store energy in an LC oscillator?
A capacitor stores energy in the form of an electrostatic field.
How does an inductor store energy in an LC oscillator?
An inductor uses a magnetic field to store energy.
Describe the process in an LC oscillator circuit involving a tank circuit and the flywheel effect.
When the capacitor is charged with a battery and the inductor is inserted into the circuit, the capacitor will discharge through the inductor. The inductor will create a magnetic field and then try to keep the current moving in the circuit, leading to an oscillation between the capacitor and inductor.
What happens once the capacitor discharges?
The inductor tries to keep the current moving by charging up the other plate of the capacitor
What happens when the inductor's field collapses?
The capacitor is recharged with the opposite polarity and discharges again through the inductor
What causes the oscillation in the circuit?
The interaction between the inductor and capacitor until the circuit runs out of energy due to resistance in the wire
What determines the frequency of oscillation in an LC tank circuit?
The size of the inductor and the capacitor
What is used to restore lost energy and provide a constant amplitude sine wave output in an LC oscillator?
An amplifier
What is the resulting waveform in an LC oscillator known as?
Continuous wave (CW)
What are LC oscillators essentially in terms of circuitry?
Feedback amplifiers with the feedback helping to increase or sustain the self-generated output
What are the criteria for oscillation stated by the Barkhausen criteria?
1. The loop gain must be 1 (unity) 2. The loop phase shift must be n * 360 degrees, where n is any integer
What type of oscillators are crystal oscillators?
Oscillators utilizing crystals, most commonly quartz
Describe the ideal oscillator circuit according to the Barkhausen criteria.
The ideal oscillator circuit has a loop gain initially greater than 1 when signals are small, decreasing to 1 as the signal reaches the desired amplitude.
What are the types of oscillator circuits?
1. Hartley Oscillators. 2. Colpitts Oscillators. 3. Clapp Oscillators. 4. Crystal Oscillators.
How do crystal oscillators work based on the text?
A crystal oscillator circuit amplifies a voltage signal from a quartz resonator and feeds it back to the resonator, sustaining oscillation. The quartz crystal behaves like a circuit composed of an inductor, capacitor, and resistor with a precise resonant frequency.
What is the electrical equivalent circuit of a quartz crystal?
Inductor, capacitor, and resistor with a precise resonant frequency
How does a crystal oscillator circuit sustain oscillation?
By taking a voltage signal from the quartz resonator, amplifying it, and feeding it back to the resonator
What determines the resonant frequency of a crystal oscillator circuit?
The rate of expansion and contraction of the quartz, determined by the cut and size of the crystal
What is modulation?
Mixing of low frequency signals (modulating signal) with high frequency signals (carrier signal), where some characteristic of a high frequency sine wave is varied in accordance with the instantaneous value of the signal. It is the imposition of information on a given signal or the modification of one signal by another signal.
What are the 3 types of modulation according to the carrier used?
Continuous Wave-carrier is a sinusoid Pulse - carrier is a train of pulses (discrete)
What are the 2 types of modulation according to the method used?
Analog modulation, Digital modulation
What are 5 reasons for modulation?
1. To reduce antenna lengths. 2. To reduce noise interference. 3. For frequency assignments. 4. For multiplexing. 5. To overcome equipment limitations.
What is analog modulation?
Analog modulation includes techniques like Amplitude Modulation (AM).
What is phase modulation?
Modulating the phase of a carrier signal to transmit information.
What is angle modulation?
A term that refers to both phase modulation and frequency modulation.
What is frequency modulation?
Modulating the frequency of a carrier signal to transmit information.
What is digital modulation?
Modulating digital signals to transmit information through a carrier signal.
What is pulse code modulation?
A method for converting analog signals to digital signals for transmission.
What is delta modulation?
A form of modulation where the difference between consecutive signal samples is transmitted.
What is the relationship between instantaneous amplitude and peak amplitude in a sinusoidal signal?
Instantaneous amplitude can vary but peak amplitude remains constant.
What does 't' represent in a sinusoidal signal?
Instantaneous time or time variable in the signal.
What does 'f' represent in a sinusoidal signal?
Angular frequency or frequency of the signal.
Explain the concept of modulation.
Modulation is the process of encoding information from voice, video, or digital signals onto a carrier signal.
What happens in amplitude modulation (AM)?
The information signal modulates the amplitude of the carrier sine wave.
What does the envelope of a carrier waveform connect in amplitude modulation?
Connects the positive and negative peaks of the carrier waveform.
What is the purpose of modulating a carrier signal?
To transmit information effectively by varying certain characteristics of the carrier signal.
What is Amplitude Modulation (AM)?
Amplitude Modulation (AM) is a modulation technique in which the amplitude of a carrier wave is varied in proportion to the waveform of the modulating signal.
What is the modulation index (m) in AM?
The modulation index (m) in AM is a value that describes the relationship between the amplitude of the modulating signal and the amplitude of the carrier signal. It is also known as the modulating factor, coefficient, degree of modulation, or depth of modulation.
What does the modulation index describe in AM?
The relationship between the amplitude of the modulating signal and the amplitude of the carrier signal.
What are some other names for the modulation index?
Modulating factor, coefficient, degree of modulation, depth of modulation.
What is the range of values for the modulation index in AM?
0 to 1.
What are side frequencies or sidebands generated as part of the modulation process?
Side frequencies or sidebands are generated as part of the modulation process and occur in the frequency spectrum directly above and below the carrier frequency.
How many sidebands are generated by a single frequency sine wave modulation?
Single frequency sine wave modulation generates TWO sidebands.
What type of wave generates a range of sidebands in modulation?
Complex wave (e.g., voice or video modulation) generates a range of sidebands.
What is the AM wave in modulation?
The AM wave is the algebraic sum of the carrier and upper and lower sideband sine waves.
What is the relationship between the time and frequency domains in modulation?
The relationship between the time and frequency domains in modulation is determined by the modulation index. The higher the modulation index, the higher the output power.
What is the criterion for determining whether a signal is overmodulated?
To determine if a signal is overmodulated, compare the peak value of the modulated wave to the carrier wave peak value. If it exceeds 1, the signal is overmodulated.
What is the relationship between modulation index and output power in an AM signal?
Higher the modulation index, higher the output power.
What are the sideband frequencies and total bandwidth for an AM broadcast station transmitting modulating frequencies up to 5 kHz on a frequency of 980 kHz?
Sideband frequencies: 975 kHz and 985 kHz, Total bandwidth: 10 kHz
Define simultaneous modulation.
Modulation by several carriers
What is the bandwidth formula for Amplitude Modulation (AM)?
BW = 2 x fm
What important notes are highlighted in key points regarding modulation?
a) Information is present only in the sidebands. b) During 100% modulation, 2/3 of the total power is wasted in the carrier, with the carrier power percentage being 66-67% of the transmitted AM. c) Information on the LSB is essential in modulation.
What is angle modulation used for?
Angle modulation is used for radio broadcasting, sound signal in TV, two-way fixed and mobile radio systems, cellular telephone systems, and satellite communications.
What is Phase Modulation (PM)?
Phase Modulation (PM) is a modulation wherein the phase of the carrier is made proportional to the instantaneous value of the modulating signal.
What is Carrier or Frequency deviation (f_d) in Phase Modulation?
Carrier or Frequency deviation (f_d) is the amount of change in carrier frequency produced by the modulating signal. The frequency deviation rate is how many times per second the carrier frequency deviates above or below its center frequency.
When does a frequency shift occur in Phase Modulation (PM)?
A frequency shift occurs in Phase Modulation (PM) only when the modulating signal amplitude varies.
What is the relationship between the Modulating Signal and Carrier Deviation in Phase Modulation (PM)?
In Phase Modulation (PM), the carrier deviation is proportional to both the modulating frequency and the amplitude. The frequency deviation is directly proportional to the amplitude of the modulating signal.
What is the relationship between frequency deviation and the amplitude of the modulating signal in PM?
Directly proportional
What factors affect the carrier deviation in PM?
Modulating frequency and amplitude
Type of angle modulation where carrier frequency is varied relative to modulating frequency signal
Frequency modulation (FM)
What is the relationship between the peak voltage of the carrier signal (c) and the modulation index (m) in frequency modulation (FM)?
The modulation index (m) is 2 times the frequency of the peak voltage of the carrier signal (c).
What happens to the carrier frequency in FM as the modulating signal amplitude increases?
When the modulating signal amplitude increases, the carrier frequency also increases in FM.
Explain the behavior of the carrier in FM with no modulation.
In FM, with no modulation, the carrier is at its normal center or resting frequency. The carrier amplitude remains constant in FM while the carrier frequency is changed by the modulating signal.
What is Frequency Deviation?
The amount of change in carrier frequency produced by modulating signal.
Where does the maximum frequency deviation occur in FM modulation?
At the maximum amplitude of the modulating signal.
What is Carrier Swing (CS) in FM modulation?
The total variation in frequency of the carrier.
What is Modulation Index in FM signals?
The modulation index determines the number of significant sidebands in an FM signal. It is directly proportional to the modulating voltage and inversely proportional to the modulating signal frequency.
What is Deviation Ratio in FM modulation?
The ratio of the maximum permissible frequency deviation to the maximum permissible modulating frequency.
What are the main differences between Wideband FM and Narrowband FM?
Wideband FM is used for FM broadcast, entertainment, and mobile communications with higher modulation indices and maximum deviations, while Narrowband FM is used for voice transmissions with lower modulation indices and maximum deviations.
What are the practical limits to the modulation index and frequency deviation in FM signals?
There are no theoretical limits, but practical limits are set by a compromise between signal-to-noise ratio and bandwidth. Government regulations also limit the bandwidth in terms of maximum frequency deviation and the maximum modulation frequency.
What does the modulation index 'm' represent in FM broadcasting?
The modulation index represents the ratio of the frequency deviation to the modulating frequency in FM broadcasting.
What are the typical values for modulation index 'm' in FM broadcasting?
The typical values for modulation index 'm' in FM broadcasting range from 5 to 2500.
What is Narrowband FM (NBFM) used for in FM broadcasting?
Narrowband FM (NBFM) is used for voice transmissions in FM broadcasting.
What is Wideband FM (WBFM) used for?
WBFM is used for most applications except for voice transmissions, with higher modulation indices and maximum deviations.
What complex mathematical process is used to solve the equation that expresses the phase angle in terms of the sine wave modulating signal in FM?
Bessel functions
What is the name of the coefficients widely available for solving the equation using Bessel functions in FM?
Bessel coefficients
How does the bandwidth of an FM signal change with higher modulation index?
It increases, resulting in a greater number of significant sidebands and wider signal bandwidth.
How can the bandwidth of an FM signal be restricted when spectrum conservation is necessary?
By putting an upper limit on the modulation index
What function is used to illustrate the corresponding frequency spectrum of an FM wave in this problem?
Bessel function is used to illustrate the corresponding frequency spectrum of an FM wave.
What is the relationship between transmitted power and depth of modulation in FM?
In FM, the total transmitted power remains constant but with increased depth of modulation, the required bandwidth is increased.
What are the components in the block diagram of an FM transmitter?
RF oscillator - Exciter (providing an FM RF signal) - Power amplifier and connected below the exciter we have - Pre-emphasis network-Audio amplifier
What is pre-emphasis in the context of FM transmission?
Pre-emphasis is the boosting of the higher modulating frequencies at the transmitter to improve noise immunity at FM and prevent degradation of the higher frequency components of the transmitted intelligence.
What is de-emphasis in FM receivers and what is the time constant for the pre-emphasis and de-emphasis networks?
De-emphasis is reducing the amplitude of higher modulating frequencies at the receiver. The time constant for both pre-emphasis and de-emphasis networks is 75 us (or 150 us for Europe, 25 us for Dolby) with a cutoff frequency of 2122 Hz.
What is the Image Frequency effect in FM?
Effect of two stations being received simultaneously
What is Co-channel Interference in FM?
Interference true to mobile receivers when travelling from one transmitter toward another, minimized by capture effect
How does FM minimize interference from undesired signals and noise?
By capturing the strongest signal or station and minimizing other signals operating on the same frequency
What is Adjacent Channel Interference in FM?
Interference created between tuning two adjacent stations due to imperfections in filter circuits
What is the Stereophonic FM Multiplex System?
A 1961 modulation system in which left and right channels are transmitted simultaneously and independently
What are the different types of FM demodulators?
Slope Detector, Pulse Averaging Discriminators, Quadrature Detector, Phase Locked Loops, Foster Seeley Discriminator
What is the Indirect Method for FM demodulation known as?
FM Armstrong Method
How is Wideband FM obtained in the FM Armstrong Method?
By successive frequency multiplication of the output from a balanced modulator and a crystal that is shifted 90 degrees
What are the various types of demodulators for FM signals?
1. Slope Detector 2. Pulse Averaging Discriminators 3. Quadrature Detector 4. Phase Locked Loops 5. Foster Seeley Discriminator
What are the methods used in FM demodulation?
1. Indirect Method 2. Armstrong Method
How is the modulating signal modulated before FM demodulation?
It is modulated using a balanced modulator.
What device is used in combination with the modulated signal in FM demodulation to obtain Wideband FM?
Crystal oscillator
What is the process to obtain Wideband FM in FM demodulation?
Successive frequency multiplication of the output
What components are involved in the process of FM demodulation for Wideband FM?
Crystal oscillator, Buffer, Phase shifter, Combining network, Balanced Modulator
What are the characteristics of FM waves in terms of carrier frequency (f c) and modulation frequency (m f)?
1. Low f c and m f - Carrier only 2. Medium f c and low m f - Low sidebands 3. High f c and m f - High sidebands
What type of modulation involves shifting the carrier frequency (f c) by 90 degrees?
Armstrong Modulation
What is the carrier swing when the oscillator deviates 2kHz in an FM transmitter with two doublers and one tripler?
d) 48kHz
What principle do FM receivers utilize?
Superheterodyne principle
What frequency range do FM receivers operate in?
88-108 MHz
What is used in FM receivers to ensure the received signal is constant in amplitude before it enters the discriminator or detector?
Limiter
What causes interference in the form of noise in FM signals?
Lightning, motors, automotive ignition systems, power line switching
What is the role of limiter circuits in FM receivers in terms of amplitude of the received signal?
Limiter circuits restrict the amplitude of the received signal
How does FM offer noise immunity compared to AM signals?
FM has superior immunity to noise due to clipper limiter circuits in the receiver
What effect helps FM signals reject interfering signals on the same frequency?
Capture effect
What is the purpose of limiter circuits in an FM signal?
To clip amplitude variations and preserve the frequency variations of the carrier signal.
How does amplitude clipping in FM signals affect the information content?
It does not affect the information content as it is contained within the frequency variations of the carrier signal.
What is the noise suppression effect of FM signals?
FM signals have superior noise immunity due to clipper limiter circuits in the receiver.
Explain the capture effect in FM signals.
The capture effect in FM signals refers to the rejection of interfering signals on the same frequency.
What is a benefit of FM signals over AM signals in terms of power efficiency?
FM signals do not require linear amplifiers to increase power levels, leading to increased transmitter efficiency.
What are some disadvantages of FM?
FM uses considerably more frequency spectrum space and has used more complex circuitry for modulation and demodulation.
What has happened with the complex circuitry used in FM with the proliferation of ICs?
With the proliferation of ICs, the complex circuitry used in FM has all but disappeared as ICs are inexpensive and easy to use.
What are the major applications of AM and FM?
The major applications of AM and FM include electronic communication.
What is the significance of human communication?
Communication is the process of exchanging information, with main barriers being language and distance. Contemporary society emphasizes the accumulation, packaging, and exchange of information.
What are some methods of communication?
Face to face, signals, written word (letters), and electrical innovations such as telegraph, telephone, radio, television, internet, and computer.
Untitled Flashcards
Study
What is a decibel?
A unit used in electrical engineering and acoustics to express on a logarithmic scale the ratio between two values with the same dimensions.
What are the quantities compared using decibels?
Two voltages, two power levels, two sound pressure levels, and so on.
What are the three factors that affect the extent of damage to hearing caused by noise?
1. Decibel level (how loud the sound is) 2. Distance (how close you are to the source of the sound) 3. Time (the length of time you are exposed to the sound)
How is sound measured?
Sound is measured in units called decibels (dB).
What is the significance of A-weighted decibels (dBA)?
A weighted decibels can be used to describe sound based on what human ears can actually hear, as people can't hear all frequencies or pitches of sound.
What decibel level is generally considered safe for sounds?
Sounds at or below 70 dBA are generally considered safe.
At what decibel level is sound more likely to damage hearing over time?
Any sound at or above 85 dBA is more likely to damage hearing over time.
What is the increased risk for hearing loss associated with noise levels of 85 dBA or higher?
People exposed to such noise levels over long periods are at a much greater risk for hearing loss.
Why are some workers required to wear hearing protectors like earplugs or earmuffs?
To protect their hearing from noise levels at or above 85 dBA while they are on the job.
What decibel level is generally considered safe for human ears?
Sounds at or below 70 dBA
At what decibel level are sounds more likely to damage hearing over time?
Any sound at or above 85 dBA
What is the risk for hearing loss for people exposed to noise levels at 85 dBA or higher over long periods of time?
Much greater risk
Why are some workers required to wear hearing protectors like earplugs or earmuffs on the job?
To protect their hearing from exposure to high decibel levels
What are some factors that affect hearing loss?
Decibel level, distance, and time
What is the decibel level of many devices that children use today?
Higher than 85 dBA
How intense is 110 dBA compared to 85 decibels?
More than 100 times as intense
Are manufacturers required to limit the maximum sound output of music devices?
No, they are not required to do so
What can volume limiting controls on devices help with?
Setting the maximum volume to a safe level
How does the sound level change as you move closer or further away from the source?
It gets louder as you move closer and softer as you move away
In what situation at a concert can reduce the risk of hearing damage?
Sitting away from the speakers
What impact does exposure to loud sounds on a regular basis have on the risk of hearing damage?
It increases the risk for permanent damage over time
What is considered safe sound levels that last a long time?
Sounds at or below 70 dBA
At what decibel level and duration is it more likely for noises to damage hearing?
85 dBA lasting a few hours, 100 dBA lasting at least 14 minutes, 110 dBA lasting at least 2 minutes
Why is decibel notation mainly used in calculating signal levels?
It is convenient for calculating signal levels
What is the risk of permanent damage to hearing if exposed to loud sounds on a regular basis?
Increases over time
What is the potential effect of a single but long-lasting loud event on hearing?
Can cause damage
What is the considered safe level for sounds that last a long time?
70 dBA or below
At what sound level and duration are noises more likely to damage hearing?
85 dBA for a few hours, 100 dBA for at least 14 minutes, 110 dBA for at least 2 minutes
What is the main reason for using decibel notation in calculating signal levels?
Convenience
When working with decibel values, what operation can be performed with dB values?
Decibel values can only be added or subtracted
How could the operation of adding individual gains of two amplifiers in cascade be interpreted in terms of dB?
It could be interpreted as adding the individual dB gains to get the overall gain of the combination
How could the operation of getting the net gain of an amplifier and a lossy section be interpreted in terms of dB?
It could be interpreted as subtracting the dB loss from the dB gain to get the net gain
What is correlated noise?
Unwanted electrical energy that interferes with the desired signal
What is correlated noise?
Unwanted electrical energy that is used before it is transmitted, and falls into two categories.
What are the two categories of noise?
1. Correlated noise 2. Uncorrelated noise
What is noise in the context of signal transmission?
Any unwanted or undesirable signal that interferes with the desired signal.
How can noise affect a signal in the medium?
Noise can affect the signal in the medium as there is no factor to protect the signal except for the type of modulation used before transmission.
What are the two categories of noise?
1. Correlated Noise 2. Uncorrelated Noise
What is correlated noise?
Unwanted electrical energy present as a direct result of a signal, such as harmonic and intermodulation distortion.
What are the two types of correlated noise?
a. Intermodulation Distortion b. Harmonic Distortion
What is uncorrelated noise?
Noise present regardless of whether there is a signal or not.
What are the two types of uncorrelated noise?
a. External Noise b. Internal Noise
What is external noise?
Noise produced by devices or equipment made by humans that affects frequencies up to 500MHz.
What are the sources of external noise?
1. Industrial Man-Made Noise 2. Static Atmospheric Noise 3. Space (Extra Terrestrial) Noise
What is industrial man-made noise?
Noise produced by devices or equipment made by humans, affecting frequencies up to 500MHz. Example sources are combustion engines, fluorescent lamps, switches, etc.
What is static atmospheric noise?
Noise coming from lightning discharges during thunderstorms, rain, and dust storms. It greatly affects frequencies below 30MHz.
What is space (extra-terrestrial) noise?
Noise coming from sources like the sun, solar noise, stars, cosmic noise, and galaxies. It is observable between 8MHz to 143GHz.
What is solar noise?
The noise intensity produced by the sun, varying with time and having a repeating 11-year cycle. During its peak cycle, a tremendous amount of noise is produced.
How is solar noise intensity affected by the sun's activity?
Solar noise intensity varies with time and has a repeating 11-year cycle, with a peak cycle producing a significant amount of noise.
What are some examples of sources of electromagnetic noise in the environment?
Combustion engines, fluorescent lamps, switches, etc.
What is static atmospheric noise and when does it greatly affect frequencies?
Static atmospheric noise is noise coming from lightning discharges during thunderstorms and rain/dust storms. It greatly affects frequencies below 30 MHz.
What is space or extraterrestrial noise and what are some sources of it?
Space or extraterrestrial noise is noise coming from the sun, solar noise, stars, cosmic noise, and galaxies. Sources include sun, stars, cosmic noise, and galaxies.
What is solar noise and how does it affect radio signal interference during its peak cycle?
Solar noise is the noise intensity produced by the sun, which varies with time in a repeating 11-year cycle. During its peak cycle, a tremendous amount of noise is produced causing radio signal interference and making many frequencies unusable for communications.
What is cosmic noise and what frequency range does it affect the most?
Cosmic noise is noise coming from stars and affects the frequency range from 10 MHz to 15 GHz, with the greatest disruptions in the 15 to 150 MHz range. Sources include Cassiopeia A and Cygnus A.
What is internal noise and what are some names it is known by?
Internal noise is noise coming from the rapid and random motion of charge carriers inside a resistive component when heated. It is also known as Johnson noise, thermal noise, white noise, or Gaussian noise.
What is the frequency range affected by stars and cosmic sources in terms of EMF interference?
10MHz to 15GHz, with the greatest disruptions in the 15 to 150 MHz range
What are two of the strongest sources of EMF interference from stars.
Cassiopeia A and Cygnus A
What is Johnson noise, and why is it also known as thermal noise?
Noise from rapid and random motion of charge carriers in a resistive component when heated; named after J.B. Johnson and is temperature dependent
Shot Noise Definition:
Shot noise is the major contribution of transistor noise due to shot effect. Current carriers in semiconductors have a discrete particle nature.
What is the major contribution of transistor noise due to shot effect?
Shot noise
What type of noise is also known as 1f noise, flicker noise, excess noise, or modulation noise found in transistors?
PINK NOISE
What is transit time noise and where does it occur?
Transit time noise is a kind of noise that occurs in transistors. Transit time refers to the duration of time it takes for a current carrier like a hole or electron to move from input to output. The effect of this noise can be seen in high-frequency operation.
What is resistance noise and what are its contributors?
Resistance noise is due to the base, emitter, and collector internal resistance of a transistor.
What is burst noise, and where is it observed in transistors?
Burst noise, also known as popcorn noise, is a low-frequency noise observed in BJT (Bipolar Junction Transistor) that appears as a series of bursts of two or more levels.
What is avalanche noise and what causes it?
Avalanche noise is large noise spikes due to collisions that result in an avalanche action in a device.
What is partition noise?
Partition noise refers to random fluctuations in the division of current in two or more electrodes.
What is impulse noise characterized by?
Impulse noise is non-continuous, consisting of irregular pulses or noise spikes of short duration and relatively high amplitude. The spikes are called HITS (High Impulse Transient Signals).
What is avalanche noise?
Large noise spikes due to collisions that result in a valanching action.
What is partition noise?
Random fluctuations in the division of current in two or more electrodes.
What is impulse noise?
A non-continuous noise consisting of irregular pulses or noise spikes of short duration and relatively high amplitude.
What is the Signal-to-Noise Ratio (SNR) usually expressed in?
Power, because the received signal is also expressed in terms of power.
What is Noise Factor (NF), Noise Ratio (NR), and Noise Figure (F) related to?
They are related to the signal-to-noise ratio.
What is used to specify how noisy a device is in terms of noise figure?
Noise Figure
What is used to identify the noise content at a specific point but is not useful in relating how much additional noise a device has injected into a signal going from input to output?
Signal-to-Noise Ratio (SNR)
What do each amplifier in a cascaded string of amplifiers produce over and above the thermal noise?
Noise
What happens to the amount of noise generated by succeeding stages as the input signal and noise is amplified in cascaded amplifiers?
Adds relatively very little to the overall amount of noise
What is the significant effect of reactive circuits on noise in terms of frequency response?
Limitation on frequency response, affecting the effective bandwidth
What is the significant effect of reactive circuits on noise?
Limitation on frequency response
What does a reactive circuit's limitation on frequency response result in?
Effective or equivalent bandwidth
What is the effective noise bandwidth for a 3dB bandwidth of 500Hz determined by an RC circuit used in an amplifier system?
The effective noise bandwidth is determined by the 3dB bandwidth of 500Hz.
What is noise temperature and how is it related to thermal noise in devices?
Noise temperature is a measure of noise in a system due to thermal noise, which is directly proportional to temperature.
When is noise temperature most appropriate to use, and what does a lower noise temperature indicate?
Noise temperature is most appropriate for circuits operating at VHF, UHF, or microwave frequencies. A lower noise temperature indicates a better circuit, especially for low noise systems like masers and parametric preamplifiers.
What does SINAD stand for?
Signal plus Noise plus Distortion to Noise plus Distortion ratio
How is the SINAD ratio calculated?
SINAD = (Signal + Noise + Distortion power) / (Noise + Distortion power)
Why does the residual audio power exist in a communication system?
Due to the fact that amplifiers and other circuits in a receiver are not perfectly linear and introduce distortion
What form does the distortion take in a communication system?
The distortion takes the form of very low levels of signal harmonics
How do harmonics and noise affect the signal in a communication system?
Harmonics add to the signal along with the noise
What does SINAD ratio stand for in relation to signal quality in a communication system?
Signal-to-Noise-and-Distortion ratio
What is the role of the SINAD ratio in a communication system?
SINAD ratio makes no attempt to discriminate between or separate the noise and distortion signals
What is noise in the context of signal transmission?
Any unwanted or undesirable signal tending to interfere with the desired or wanted signal.
How can noise affect a signal in a medium?
Noise can affect the signal in the medium as there is no factor that can protect it when traveling aside from the type of modulation used before transmission.
What are the two categories of noise mentioned in the text?
1. Correlated Noise 2. Uncorrelated Noise
What is correlated noise?
Unwanted electrical energy present as a direct result of a signal, such as harmonic and intermodulation distortion.
Name the two types of correlated noise mentioned in the text.
a. Intermodulation Distortion b. Harmonic Distortion
Define uncorrelated noise.
Noise present regardless of whether there is a signal or not.
List the two types of uncorrelated noise discussed in the text.
a. External Noise b. Internal Noise
What is industrial man-made noise?
Noise produced by devices or equipment made by humans and affects frequencies up to 500MHz. Examples include combustion engines, fluorescent lamps, and switches.
What is static atmospheric noise?
Noise originating from lightning discharges during thunderstorms, rain, and dust storms. It has an inverse relationship with frequency and notably affects frequencies below 30 MHz.
What is space extraterrestrial noise?
Noise sourced from the sun, solar noise, stars, cosmic noise, and galaxies such as galactic noise. Observable between 8MHz to 143GHz.
Explain the 11-year noise cycle associated with solar noise.
The noise intensity produced by the sun varies with time, following an 11-year cycle. During its peak cycle, a tremendous amount of noise is produced.
What is combustion engine an example of?
Combustion engine is an example of a source of noise.
What is the frequency range affected by STATIC ATMOSPHERIC NOISE?
STATIC ATMOSPHERIC NOISE greatly affects frequencies below 30 MHz.
Where does SPACE EXTRA TERRESTRIAL NOISE come from?
SPACE EXTRA TERRESTRIAL NOISE comes from sources such as the sun, solar noise, stars, cosmic noise, and galaxies.
What is the frequency range observable for SPACE EXTRA TERRESTRIAL NOISE?
SPACE EXTRA TERRESTRIAL NOISE is observable between 8MHz to 143GHz.
What is the 11 year noise cycle related to SOLAR NOISE?
The 11 year noise cycle related to SOLAR NOISE is the varying noise intensity produced by the sun.
What disturbances in the ionosphere are caused by the sun during its peak cycle?
During its peak cycle, the sun causes disturbances in the ionosphere known as SIDs (Sudden Ionospheric Disturbances) due to solar flares and ionospheric storms.
What is the frequency range affected by COSMIC or GALACTIC NOISE?
COSMIC or GALACTIC NOISE affects the frequency range from 10MHz to 15GHz, but causes the greatest disruptions in the 15 to 150 MHz range.
Who is J.B. Johnson and why is noise related to him?
J.B. Johnson studied Johnson or Thermal or White Noise, which is noise coming from the rapid and random motion of charge carriers inside a resistive component when heated. It is also known as thermal noise.
What is internal noise also known as?
Johnson, thermal, white, or Gaussian noise
Who thoroughly studied Johnson noise in 1928?
J.B. Johnson
What is the major contribution of transistor noise due to shot effect?
Shot noise
Describe the nature of current carriers in all forms of semiconductors.
Current carriers have a discrete particle nature
What is pink noise also known as?
1f noise, flicker noise, excess noise, modulation noise
What is transit time noise and in which devices does it occur?
Noise that occurs in transistors due to the time it takes for a current carrier to move from input to output
What is resistance noise attributed to in transistors?
Internal resistance of the base, emitter, and collector
What is burst noise also known as and where is it observed?
Popcorn noise, observed in BJT transistors as bursts of two or more levels
What is the issue of noise in mixers compared to amplifiers?
Low transconductance and inadequate image frequency rejection
What is avalanche noise characterized by?
Large noise spikes due to collisions resulting in avalanche actions
What is partition noise characterized by?
Random fluctuations in the division of current in two or more electrodes
What is impulse noise composed of?
Irregular pulses or noise spikes of short duration and high amplitude, also known as HITS
Define signal-to-noise ratio.
A ratio used to measure the level of a desired signal compared to the level of background noise present
What is avalanche noise?
A large noise spikes due to collision that result in a valanching action
What is partition noise?
Random fluctuations in the division of current in two or more electrodes
What is impulse noise?
A non-continuous noise consisting of irregular pulses or noise spikes of short duration and relatively high amplitude
How is signal to noise ratio (SNR) usually expressed?
In power because the received signal is also expressed in terms of power
What are the units of measurement for inductance and capacitance in RF circuits?
Henries for inductance and Farads for capacitance
What is the quality (Q) of a component in RF circuits?
A measure of the energy stored to that which is lost in the component
What does R represent in an inductor in RF circuits?
Series resistance distributed along the windings
What does G represent in a capacitor in RF circuits?
Value of conductance through the dielectric between the capacitor plates
Define resonance in a circuit
Circuit condition where inductive and capacitive reactance are balanced (X L = X C )
What is the resonant frequency of a circuit and how is it expressed?
Frequency at which X L = X C ; expressed as f r
What is an RLC circuit and what components does it consist of?
Electrical circuit consisting of a resistor, inductor, and capacitor connected in series or parallel
What is the impedance of a series RLC circuit at its resonant frequency?
Minimum and equal to the value of the resistor (R)
Describe the impedance of a series RLC circuit at low and high frequencies
Low frequencies: high impedance due to high Xc; High frequencies: high impedance due to high X L
What happens to the impedance of a series RLC circuit at resonance (f = f r )?
Z = R, impedance is at its minimum value
What is an RLC circuit in series composed of?
A resistor, an inductor, and a capacitor connected in series
When is the impedance of a series RLC circuit minimum?
At its resonant frequency, where it is equal to the value of the resistor (R)
Why is the impedance of a series RLC circuit high at low frequencies?
Because the reactance of the capacitor (XC) is high at low frequencies
Why is the impedance of a series RLC circuit high at high frequencies?
Because the reactance of the inductor (XL) is high at high frequencies
What is the passband of a filter?
The band of frequencies that a filter allows to pass through without attenuation
What is the stopband of a filter?
The band of frequencies that a filter attenuates or blocks from passing through
What is the cutoff frequency of a filter?
The frequency at which the power output is reduced to 12 of the passband power, equivalent to a voltage or amplitude reduction to 707 of the passband
What is another term for the cutoff frequency of a filter?
Also known as the knee frequency, break frequency, or corner frequency
What is the cutoff frequency often referred to as in relation to the filter response?
The 3 dB point, as it is where the filter response drops down by 3 dB from the value of the passband response
What is the cutoff frequency (fc) in a filter response?
The frequency where the filter response drops down 3dB from the value of the passband response.
What does the cutoff frequency (fc) signify in terms of power output?
The frequency either above or below which the power output is reduced to 1/2 of the passband power (12 of passband power).
What is the significance of the cutoff frequency (fc) in terms of voltage or amplitude reduction?
Equivalent to a voltage or amplitude reduction to 0.707 of the passband.
What is another term used to refer to the cutoff frequency (fc)?
The 3 dB point, knee frequency, break frequency, or corner frequency.
What is the band of frequencies being rejected and a notch being cut into the output at the resonant frequency called?
Band reject or notch filter, sometimes referred to as a trap.
What is the resonant frequency (fr) for a circuit, and how is it determined?
The frequency at which a resonance occurs in the circuit. It can be determined by analyzing the circuit's components and characteristics.
What is the response curve seen in a bandpass filter configuration?
The response curve shows a peak response within a specific frequency range, known as the bandwidth of the filter.
What is the bandwidth (BW) of a filter
The frequency range between the high cutoff frequency (f hc) and low cutoff frequency (f lc).
What is the frequency range between f_lc and f_hc called in a bandpass filter?
Bandwidth (BW)
What does the quality factor Q of a filter measure?
Q provides a measure of how selective and narrow the passband of the filter is compared to its center frequency (fr).
As the quality factor Q of a filter increases, what happens to the filter's selectivity?
As Q increases, the filter becomes more selective, meaning a smaller passband and narrower bandwidth is allowed.
What is the limiting factor for the selectivity of a filter in terms of inductors?
The turns of wire and associated resistance used to make an inductor provide the limiting factor for the filter's selectivity.
What is a parallel LC circuit also known as?
A parallel LC circuit is sometimes called a tank circuit.
When is the resonant frequency of a parallel LC circuit reached in terms of the quality factor Q?
The transfer of energy between the inductor and capacitor in a parallel LC circuit occurs at a natural rate equal to the resonant frequency when Q is greater than 10 (Q>10).
What is a tank circuit also known as?
A parallel LC circuit
How is energy stored in a tank circuit?
Energy is stored in each reactive elements L and C, first in one then released to the other
At what rate does the transfer of energy between the two elements occur in a tank circuit?
At the resonant frequency
What is the form of the energy transfer between elements in a tank circuit?
Sinusoidal
What are the types of filters mentioned in the text?
1. Active filters 2. Passive filters
Define active filters
Filters that use an amplifier with passive elements to provide pass or reject characteristics
Define passive filters
Filters that contain only passive, non-amplifying components and provide pass or reject characteristics
What does an active device provide in terms of filters?
Voltage gain
What does a passive device provide in terms of filters?
Frequency selectivity
What is the definition of an octave in terms of frequency?
Change in frequency by a factor of 2
What is the definition of a decade in terms of frequency?
Change in frequency by a factor of 10
What is the roll-off rate in filters?
Rate of transition from passband to stopband or vice versa
List the categories of filters
1. Low pass 2. High pass 3. Band pass 4. Band stop
Describe a high pass filter
A filter that passes high frequencies well but attenuates or reduces frequencies lower than the cutoff frequency
Describe a low pass filter
A filter that passes low frequencies well but attenuates or reduces higher frequencies than the cutoff frequency
What is the roll off rate in the context of filters?
The rate of transition from passband to stopband or vice versa.
What is a band pass filter?
A filter that combines the properties of low pass and high pass filters to allow a specific range of frequencies to pass through.
What is a band stop filter also known as?
Band elimination, band reject, or notch filter.
What is a band stop filter?
Also known as a band elimination, band reject, or notch filter, this type of filter passes all frequencies above and below a particular range set by the component values.
How is the frequency response of a filter generally represented?
Using a Bode plot.
What is the rate of roll-off for an n order filter in terms of dB per octave?
6n dB per octave.
What is an oscillator in the context of communication systems?
A circuit capable of converting energy from DC into AC, capable of generating a repetitive waveform at a specified frequency.
What factors dictate the form of oscillator to be used in a given application?
Performance considerations, economic factors.
What forms of energy storage are mentioned in LC oscillators?
Capacitors and inductors store energy, with capacitors storing energy in the form of an electrostatic field.
What are the criteria used to determine the choice of oscillator type?
1. Output frequency required 2. Frequency stability required 3. Is the frequency to be variable and if so over what range 4. Allowable waveform distortion 5. Power output required
How does a capacitor store energy in an LC oscillator?
A capacitor stores energy in the form of an electrostatic field.
How does an inductor store energy in an LC oscillator?
An inductor uses a magnetic field to store energy.
Describe the process in an LC oscillator circuit involving a tank circuit and the flywheel effect.
When the capacitor is charged with a battery and the inductor is inserted into the circuit, the capacitor will discharge through the inductor. The inductor will create a magnetic field and then try to keep the current moving in the circuit, leading to an oscillation between the capacitor and inductor.
What happens once the capacitor discharges?
The inductor tries to keep the current moving by charging up the other plate of the capacitor
What happens when the inductor's field collapses?
The capacitor is recharged with the opposite polarity and discharges again through the inductor
What causes the oscillation in the circuit?
The interaction between the inductor and capacitor until the circuit runs out of energy due to resistance in the wire
What determines the frequency of oscillation in an LC tank circuit?
The size of the inductor and the capacitor
What is used to restore lost energy and provide a constant amplitude sine wave output in an LC oscillator?
An amplifier
What is the resulting waveform in an LC oscillator known as?
Continuous wave (CW)
What are LC oscillators essentially in terms of circuitry?
Feedback amplifiers with the feedback helping to increase or sustain the self-generated output
What are the criteria for oscillation stated by the Barkhausen criteria?
1. The loop gain must be 1 (unity) 2. The loop phase shift must be n * 360 degrees, where n is any integer
What type of oscillators are crystal oscillators?
Oscillators utilizing crystals, most commonly quartz
Describe the ideal oscillator circuit according to the Barkhausen criteria.
The ideal oscillator circuit has a loop gain initially greater than 1 when signals are small, decreasing to 1 as the signal reaches the desired amplitude.
What are the types of oscillator circuits?
1. Hartley Oscillators. 2. Colpitts Oscillators. 3. Clapp Oscillators. 4. Crystal Oscillators.
How do crystal oscillators work based on the text?
A crystal oscillator circuit amplifies a voltage signal from a quartz resonator and feeds it back to the resonator, sustaining oscillation. The quartz crystal behaves like a circuit composed of an inductor, capacitor, and resistor with a precise resonant frequency.
What is the electrical equivalent circuit of a quartz crystal?
Inductor, capacitor, and resistor with a precise resonant frequency
How does a crystal oscillator circuit sustain oscillation?
By taking a voltage signal from the quartz resonator, amplifying it, and feeding it back to the resonator
What determines the resonant frequency of a crystal oscillator circuit?
The rate of expansion and contraction of the quartz, determined by the cut and size of the crystal
What is modulation?
Mixing of low frequency signals (modulating signal) with high frequency signals (carrier signal), where some characteristic of a high frequency sine wave is varied in accordance with the instantaneous value of the signal. It is the imposition of information on a given signal or the modification of one signal by another signal.
What are the 3 types of modulation according to the carrier used?
Continuous Wave-carrier is a sinusoid Pulse - carrier is a train of pulses (discrete)
What are the 2 types of modulation according to the method used?
Analog modulation, Digital modulation
What are 5 reasons for modulation?
1. To reduce antenna lengths. 2. To reduce noise interference. 3. For frequency assignments. 4. For multiplexing. 5. To overcome equipment limitations.
What is analog modulation?
Analog modulation includes techniques like Amplitude Modulation (AM).
What is phase modulation?
Modulating the phase of a carrier signal to transmit information.
What is angle modulation?
A term that refers to both phase modulation and frequency modulation.
What is frequency modulation?
Modulating the frequency of a carrier signal to transmit information.
What is digital modulation?
Modulating digital signals to transmit information through a carrier signal.
What is pulse code modulation?
A method for converting analog signals to digital signals for transmission.
What is delta modulation?
A form of modulation where the difference between consecutive signal samples is transmitted.
What is the relationship between instantaneous amplitude and peak amplitude in a sinusoidal signal?
Instantaneous amplitude can vary but peak amplitude remains constant.
What does 't' represent in a sinusoidal signal?
Instantaneous time or time variable in the signal.
What does 'f' represent in a sinusoidal signal?
Angular frequency or frequency of the signal.
Explain the concept of modulation.
Modulation is the process of encoding information from voice, video, or digital signals onto a carrier signal.
What happens in amplitude modulation (AM)?
The information signal modulates the amplitude of the carrier sine wave.
What does the envelope of a carrier waveform connect in amplitude modulation?
Connects the positive and negative peaks of the carrier waveform.
What is the purpose of modulating a carrier signal?
To transmit information effectively by varying certain characteristics of the carrier signal.
What is Amplitude Modulation (AM)?
Amplitude Modulation (AM) is a modulation technique in which the amplitude of a carrier wave is varied in proportion to the waveform of the modulating signal.
What is the modulation index (m) in AM?
The modulation index (m) in AM is a value that describes the relationship between the amplitude of the modulating signal and the amplitude of the carrier signal. It is also known as the modulating factor, coefficient, degree of modulation, or depth of modulation.
What does the modulation index describe in AM?
The relationship between the amplitude of the modulating signal and the amplitude of the carrier signal.
What are some other names for the modulation index?
Modulating factor, coefficient, degree of modulation, depth of modulation.
What is the range of values for the modulation index in AM?
0 to 1.
What are side frequencies or sidebands generated as part of the modulation process?
Side frequencies or sidebands are generated as part of the modulation process and occur in the frequency spectrum directly above and below the carrier frequency.
How many sidebands are generated by a single frequency sine wave modulation?
Single frequency sine wave modulation generates TWO sidebands.
What type of wave generates a range of sidebands in modulation?
Complex wave (e.g., voice or video modulation) generates a range of sidebands.
What is the AM wave in modulation?
The AM wave is the algebraic sum of the carrier and upper and lower sideband sine waves.
What is the relationship between the time and frequency domains in modulation?
The relationship between the time and frequency domains in modulation is determined by the modulation index. The higher the modulation index, the higher the output power.
What is the criterion for determining whether a signal is overmodulated?
To determine if a signal is overmodulated, compare the peak value of the modulated wave to the carrier wave peak value. If it exceeds 1, the signal is overmodulated.
What is the relationship between modulation index and output power in an AM signal?
Higher the modulation index, higher the output power.
What are the sideband frequencies and total bandwidth for an AM broadcast station transmitting modulating frequencies up to 5 kHz on a frequency of 980 kHz?
Sideband frequencies: 975 kHz and 985 kHz, Total bandwidth: 10 kHz
Define simultaneous modulation.
Modulation by several carriers
What is the bandwidth formula for Amplitude Modulation (AM)?
BW = 2 x fm
What important notes are highlighted in key points regarding modulation?
a) Information is present only in the sidebands. b) During 100% modulation, 2/3 of the total power is wasted in the carrier, with the carrier power percentage being 66-67% of the transmitted AM. c) Information on the LSB is essential in modulation.
What is angle modulation used for?
Angle modulation is used for radio broadcasting, sound signal in TV, two-way fixed and mobile radio systems, cellular telephone systems, and satellite communications.
What is Phase Modulation (PM)?
Phase Modulation (PM) is a modulation wherein the phase of the carrier is made proportional to the instantaneous value of the modulating signal.
What is Carrier or Frequency deviation (f_d) in Phase Modulation?
Carrier or Frequency deviation (f_d) is the amount of change in carrier frequency produced by the modulating signal. The frequency deviation rate is how many times per second the carrier frequency deviates above or below its center frequency.
When does a frequency shift occur in Phase Modulation (PM)?
A frequency shift occurs in Phase Modulation (PM) only when the modulating signal amplitude varies.
What is the relationship between the Modulating Signal and Carrier Deviation in Phase Modulation (PM)?
In Phase Modulation (PM), the carrier deviation is proportional to both the modulating frequency and the amplitude. The frequency deviation is directly proportional to the amplitude of the modulating signal.
What is the relationship between frequency deviation and the amplitude of the modulating signal in PM?
Directly proportional
What factors affect the carrier deviation in PM?
Modulating frequency and amplitude
Type of angle modulation where carrier frequency is varied relative to modulating frequency signal
Frequency modulation (FM)
What is the relationship between the peak voltage of the carrier signal (c) and the modulation index (m) in frequency modulation (FM)?
The modulation index (m) is 2 times the frequency of the peak voltage of the carrier signal (c).
What happens to the carrier frequency in FM as the modulating signal amplitude increases?
When the modulating signal amplitude increases, the carrier frequency also increases in FM.
Explain the behavior of the carrier in FM with no modulation.
In FM, with no modulation, the carrier is at its normal center or resting frequency. The carrier amplitude remains constant in FM while the carrier frequency is changed by the modulating signal.
What is Frequency Deviation?
The amount of change in carrier frequency produced by modulating signal.
Where does the maximum frequency deviation occur in FM modulation?
At the maximum amplitude of the modulating signal.
What is Carrier Swing (CS) in FM modulation?
The total variation in frequency of the carrier.
What is Modulation Index in FM signals?
The modulation index determines the number of significant sidebands in an FM signal. It is directly proportional to the modulating voltage and inversely proportional to the modulating signal frequency.
What is Deviation Ratio in FM modulation?
The ratio of the maximum permissible frequency deviation to the maximum permissible modulating frequency.
What are the main differences between Wideband FM and Narrowband FM?
Wideband FM is used for FM broadcast, entertainment, and mobile communications with higher modulation indices and maximum deviations, while Narrowband FM is used for voice transmissions with lower modulation indices and maximum deviations.
What are the practical limits to the modulation index and frequency deviation in FM signals?
There are no theoretical limits, but practical limits are set by a compromise between signal-to-noise ratio and bandwidth. Government regulations also limit the bandwidth in terms of maximum frequency deviation and the maximum modulation frequency.
What does the modulation index 'm' represent in FM broadcasting?
The modulation index represents the ratio of the frequency deviation to the modulating frequency in FM broadcasting.
What are the typical values for modulation index 'm' in FM broadcasting?
The typical values for modulation index 'm' in FM broadcasting range from 5 to 2500.
What is Narrowband FM (NBFM) used for in FM broadcasting?
Narrowband FM (NBFM) is used for voice transmissions in FM broadcasting.
What is Wideband FM (WBFM) used for?
WBFM is used for most applications except for voice transmissions, with higher modulation indices and maximum deviations.
What complex mathematical process is used to solve the equation that expresses the phase angle in terms of the sine wave modulating signal in FM?
Bessel functions
What is the name of the coefficients widely available for solving the equation using Bessel functions in FM?
Bessel coefficients
How does the bandwidth of an FM signal change with higher modulation index?
It increases, resulting in a greater number of significant sidebands and wider signal bandwidth.
How can the bandwidth of an FM signal be restricted when spectrum conservation is necessary?
By putting an upper limit on the modulation index
What function is used to illustrate the corresponding frequency spectrum of an FM wave in this problem?
Bessel function is used to illustrate the corresponding frequency spectrum of an FM wave.
What is the relationship between transmitted power and depth of modulation in FM?
In FM, the total transmitted power remains constant but with increased depth of modulation, the required bandwidth is increased.
What are the components in the block diagram of an FM transmitter?
RF oscillator - Exciter (providing an FM RF signal) - Power amplifier and connected below the exciter we have - Pre-emphasis network-Audio amplifier
What is pre-emphasis in the context of FM transmission?
Pre-emphasis is the boosting of the higher modulating frequencies at the transmitter to improve noise immunity at FM and prevent degradation of the higher frequency components of the transmitted intelligence.
What is de-emphasis in FM receivers and what is the time constant for the pre-emphasis and de-emphasis networks?
De-emphasis is reducing the amplitude of higher modulating frequencies at the receiver. The time constant for both pre-emphasis and de-emphasis networks is 75 us (or 150 us for Europe, 25 us for Dolby) with a cutoff frequency of 2122 Hz.
What is the Image Frequency effect in FM?
Effect of two stations being received simultaneously
What is Co-channel Interference in FM?
Interference true to mobile receivers when travelling from one transmitter toward another, minimized by capture effect
How does FM minimize interference from undesired signals and noise?
By capturing the strongest signal or station and minimizing other signals operating on the same frequency
What is Adjacent Channel Interference in FM?
Interference created between tuning two adjacent stations due to imperfections in filter circuits
What is the Stereophonic FM Multiplex System?
A 1961 modulation system in which left and right channels are transmitted simultaneously and independently
What are the different types of FM demodulators?
Slope Detector, Pulse Averaging Discriminators, Quadrature Detector, Phase Locked Loops, Foster Seeley Discriminator
What is the Indirect Method for FM demodulation known as?
FM Armstrong Method
How is Wideband FM obtained in the FM Armstrong Method?
By successive frequency multiplication of the output from a balanced modulator and a crystal that is shifted 90 degrees
What are the various types of demodulators for FM signals?
1. Slope Detector 2. Pulse Averaging Discriminators 3. Quadrature Detector 4. Phase Locked Loops 5. Foster Seeley Discriminator
What are the methods used in FM demodulation?
1. Indirect Method 2. Armstrong Method
How is the modulating signal modulated before FM demodulation?
It is modulated using a balanced modulator.
What device is used in combination with the modulated signal in FM demodulation to obtain Wideband FM?
Crystal oscillator
What is the process to obtain Wideband FM in FM demodulation?
Successive frequency multiplication of the output
What components are involved in the process of FM demodulation for Wideband FM?
Crystal oscillator, Buffer, Phase shifter, Combining network, Balanced Modulator
What are the characteristics of FM waves in terms of carrier frequency (f c) and modulation frequency (m f)?
1. Low f c and m f - Carrier only 2. Medium f c and low m f - Low sidebands 3. High f c and m f - High sidebands
What type of modulation involves shifting the carrier frequency (f c) by 90 degrees?
Armstrong Modulation
What is the carrier swing when the oscillator deviates 2kHz in an FM transmitter with two doublers and one tripler?
d) 48kHz
What principle do FM receivers utilize?
Superheterodyne principle
What frequency range do FM receivers operate in?
88-108 MHz
What is used in FM receivers to ensure the received signal is constant in amplitude before it enters the discriminator or detector?
Limiter
What causes interference in the form of noise in FM signals?
Lightning, motors, automotive ignition systems, power line switching
What is the role of limiter circuits in FM receivers in terms of amplitude of the received signal?
Limiter circuits restrict the amplitude of the received signal
How does FM offer noise immunity compared to AM signals?
FM has superior immunity to noise due to clipper limiter circuits in the receiver
What effect helps FM signals reject interfering signals on the same frequency?
Capture effect
What is the purpose of limiter circuits in an FM signal?
To clip amplitude variations and preserve the frequency variations of the carrier signal.
How does amplitude clipping in FM signals affect the information content?
It does not affect the information content as it is contained within the frequency variations of the carrier signal.
What is the noise suppression effect of FM signals?
FM signals have superior noise immunity due to clipper limiter circuits in the receiver.
Explain the capture effect in FM signals.
The capture effect in FM signals refers to the rejection of interfering signals on the same frequency.
What is a benefit of FM signals over AM signals in terms of power efficiency?
FM signals do not require linear amplifiers to increase power levels, leading to increased transmitter efficiency.
What are some disadvantages of FM?
FM uses considerably more frequency spectrum space and has used more complex circuitry for modulation and demodulation.
What has happened with the complex circuitry used in FM with the proliferation of ICs?
With the proliferation of ICs, the complex circuitry used in FM has all but disappeared as ICs are inexpensive and easy to use.
What are the major applications of AM and FM?
The major applications of AM and FM include electronic communication.
What is the significance of human communication?
Communication is the process of exchanging information, with main barriers being language and distance. Contemporary society emphasizes the accumulation, packaging, and exchange of information.
What are some methods of communication?
Face to face, signals, written word (letters), and electrical innovations such as telegraph, telephone, radio, television, internet, and computer.
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