Chapter - 2 Analog Modulation Systems Flashcards
1
Q
It is the process of impressing low frequency information signals into a high frequency carrier signals
Also defined as the process of changing one or more properties of the analog carrier in proportion with the infromation signal
A
MODULATION
2
Q
It is the reverse process of modulation
A
Demodulation
3
Q
It is a High Frequency signal ( the one that is modulated ) used to carry information from source to destination
A
Carrier
4
Q
It is also known as Intelligence,Modulating Signal or Baseband Signal, which is understandable information (one that is modulating) such as voice , audio ,video ,documents etc
A
Information
5
Q
Advantages of Modulation
A
- practical size of antenna
* there will be no interferrence since every transmitter will use different frequencies
6
Q
Signals have longer wavelength thus they require longer antennas for transmission
A
Low Frequency
7
Q
Signals having shorter wavelength thus may require shorter antenna
A
High Frequency
8
Q
Types of Modulation
A
Analog Modulation and Digital Modulation
9
Q
Types of Analog Modulation
A
•Amplitude Modulation
•Angle Modulation
-Frequency Modulation
-Phase Modulation
10
Q
Modulation technique wherein both of the carrier and information are in analog forms
A
Analog Modulation
11
Q
It is a modulation technique invented by reginald fessenden .
Wherein the information signal is analog and the amplitude of the carrier is varied proportional to the information signal
A
AMPLITUDE MODULATION
12
Q
Standard AM range
A
535-1605khz
13
Q
Standard AM Intermediate Frequency
A
455khz
14
Q
AM Equation
A
V(t)=vcsin(wct) + (mVc/2)cos(wc-wm)t - (mVc/2)cos(wc+wm)t
15
Q
It is also known as Coefficient of Modulation or Depth of Modulation . It is the term used to describe the amount of amplitude change(modulation) present
A
AM Modulation Index
Ideally 1
Typically Less than 1
Greater than 1 will caused distortion to the signal or Overmodulation
16
Q
Modulation Index Formula
A
M=Vm/Vc
M=Vmax-Vmin/Vmax+Vmin
17
Q
It is the coefficient of modulation expressed as percentage
A
%m=m x 100%
18
Q
AM Current and Voltage
A
IT=IC(sqrt 1+m^2/2)
VT=VC(sqrt 1+m^2/2)
19
Q
AM Power Relationship
A
PT = Pc+2Psb
Psb = Pc (m^2/4)
Psbt = Pc (m^2/2)
Pt = Pc (1+m^2/2)
20
Q
AM Bandwidth Requirements
A
B(Am)=2 x fmax
21
Q
Modulation by Several Signals
A
VT = sqrt v1^2 + v2^2 ... IT = sqrt i1^2 + i2^2 ... M(eff) = sqrt m1^2 + m2^2 ...
22
Q
Is the curved produced by joining the tips of the individual RF cycles of a modulated wave . It contains the information
A
Envelope
23
Q
Useful Power in AM , Increases with Modulation becoming 1/3 of the total signal power for 100% Modulation
A
Sideband Power
24
Q
Used for observing the Modulation Characteristics of AM Transmitters
A
Trapezoidal Patterns
25
AM Transmitter
| C BIM S DAPL
```
Crystal Oscillator
Buffer Amplifier
Intermediate Power Amplifier
Modulated Power Amplifier:
-speech amplifier
-driver amplifier
-push pull modulator
Linear Power Amplifier
```
26
It provides a stable carrier frequency at low power. It is an RF oscillator which can be a hartley , colpitts , clapp etc
Crystal Oscillator
27
It is a CLASS A RF Amplifier that isolates the crystal oscillator to improve its stability
High input impedance
And Low Output Impedance
To match the high output crystal oscilator and low input IF amplifier
Buffer Amplifier
28
Class C RF amplifier that Raises the output of the buffer to a level sufficient to drive the modulated RF amplifier
It Amplifies the signal from the oscillator
Intermediate Power Amplifier
29
Class C RF amplifier that supplies the energy which is required to drive the antenna system at the rated RF power for high level modulation.
it multiplies the signals from the IF power amplifier and push pull modulator
Modulated Power Amplifier
30
It is a Class A AF pre-amplifier that raises the level of the input AF after being subjected to processing and filtering.
it amplifies the weak audio frequency so that it can be detected by the driver amplifier. it improves the Signal to Noise Ratio before mixing
Speech Amplifier
31
It is Class A/B/AB that supplies the necessary audio power to drive class B modulator.
It Amplifies the output of the speech amplifier so that it can be detected by push pull modulator
Driver Amplifier
32
It is Class B AF Output Amplifier that varies the plate voltage of the class C RF amplifier in accordance with the frequency and the amplitude of the AF signal
Push Pull Modulator
33
It is Class A/B/AB amplifier which provides linear power amplification of the amplitude-modulated output signal from the class C modulated power amplifier.
it is used for low-level modulation
Linear Power Amplifier
34
Two Types Of Amplitude Modulation
Low-Level And High-Level Modulation
35
The Modulation takes place prior to the output element of the final stage of the transmitter
Low-Level Modulation
36
The Modulation takes place in final element of the final stage where the carrier signal is at its maximum amplitude
High-Level Modulation
37
Effiency of the transmitter is calculated :
Power output / Power input
38
is used in AM amplifiers since it can be operate in high frequencies.
Common Base Configuration
39
at 100% modulation
the power of modulating amplifier is one-half of the supply power
40
AM Detection :
- Diode Envelop Detector
- Crystal Detector
- Power Detector
- Grid Leak Detector
- Regenerative Autodyne Detector
41
it is also known as peak detector. it consist of a diode in series with an RC Low pass filter. the diode acts as a rectifier that allows only one-half of the modulated AM signal to pass and the other half being clipped.
Diode Envelop Detector
42
it is the first rectifying detector. A thin,pointed wire known as CAT WHISKERS is pressed against the surface of the crystal, when a sensitive spot is found, more current flows in one direction that in the opposite thus rectification occurs
Crystal Detector
43
it is the type of detector using amplifying devices like transistors in place of a diode to provide rectification and amplification at the same time.
Power Detector
44
it consist of a tuned circuit a rectifier and an RC low pass filter for the recovery of the modulating signal. it has better sensitivity than diode detector
Grid Leak Detector
45
it employs tickler coil which is genarates energy from the plate circuit into the grid circuit of the triode.
when the regenerative detector oscillates it becomes autodyne detector (self heterodyning) or product detector and can be used to detech CW, SSB or FSK emission.
Regenerative and Autodyne Detector
46
means the extraction of the information signal from the AM signal. it is only part of the Demodulator System
Detection
47
is any frequency,phase or amplitude variations that are present in the demodulated waveform that were not in the original information signal. when noise is added to the AM signal, the Output at the detector is always Distorted
Distortion
48
it is the measure of the ability of a communication system to produce , at the output of the receiver , an exact replica of the original source information
Fidelity
49
Two Types Of AM Receiver :
- TRF (Tuned Radio Frequency) Receiver
| - SuperHeterodyne Receiver
50
one of the earliest type of AM receiver inveted by Reginald Fessenden, and is probably the simplest designed radio receivers available today.
Tuned Radio Frequency: consist of (ARDAS)
- Antenna
- RF Amplifier
- Detector
- AF Amplifier
- Speaker
51
Disadvantages Of TRF:
- Inconsistent Bandwidth
- Unstable due to large number of amplifier all tuned to the center frequency
- Gains are not Uniform over wide range of frequencies
52
it amplifies the weak RF signal. it has a variable resistor that controls the RF Gain and Sensitivity. It also Contains the pre-selector , which is used to tune to the desired frequency
RF Amplifier
53
it makes use of regenerative detector that provides rectification and detection for modulated signals. it extracts the information
Detector
54
it amplfies the recovered information (weak AF signal). it is a volume controlled amplifier that raises the power level of the AF (audio) signal to a value sufficient to drive the loudspeaker of the receiver.
AF Amplifier
55
means to mix two frequencies together in a non linear device or to translate one frequency to another using non linear mixing
Heterodyne
56
was invented by Edwin Armstrong , its gain , selectivity and sensitivity is far superior to the other receivers
Superheterodyne Receiver : consist of
- Antenna
- RF Amplifier
- Mixer and Local Oscillator
- IF Section (1st and 2nd IF amplifier)
- 2nd Detector
- AF Amplifier
- Speaker
57
it is stable crystal oscillator whose frequency beats with the incoming signal to produce the correct intermediate frequency
Local Oscillator
58
it down-convert the received RF frequencies to IFs (Intermediate Frequencies). it is the first detector which operates in a non-linear fashion and provides the action which produces the desired intermediate frequency. its outputs includes the original , sum , and difference of the local oscillator frequency and the RF input frequency.
Mixer
59
its primary functions are amplification and selectivity.
it consist of a series of IF amplifiers and bandpass filter and is often known as IF Strip. it is tuned in most cases to 455khz. it amplifies the 455khz output of the mixer and rejects the remaining output.
IF Section
60
it demodulates the 455khz IF signals and recovers the original modulating signal or audio signal
Second Detector
61
it is a receiver parameter that is used to measure the ability of the receiver to accept a given band of frequencies and reject all others
Selectivity
62
it is also known as a receiver threshold. it is the minimum RF signal level that can be detected at the input to the receiver and still produce a usable demodulated information signal
Sensitivity
63
measures just how close to perfect a tuner or tuner component can be , and its affects the bandwidth and the selectivity of a certain receiver.
Quality Factor:
Q=Fr/Bw Fr = 1/2pi(sqrt LC)
Q= XL/R
64
it is the ratio of the bandwidth 60db below maximum signal level and bandwidth 3db below maximum signal level
Shape Factor
65
it is noise reduction ratio achieved by reducing the bandwidth
Bandwidth Improvement:
| BI=B(rf)/B(if)
66
it is the corresponding reduction in the noise figure due to the reduction in bandwidth expressed mathematically in decibels.
Noise Figure Improvement :
| NFI = 10log(BI)
67
it is also known as high beat injection wherein the local oscillator frequency is tuned to a frequency higher than the input RF Frequency
High-Side Injection :
| flo=f(rf)+IF
68
it is also known as low beat injection wherein the local oscillator frequency is tuned to a frequency lower than the input RF Frequency
Low-Side Injection:
| flo=f(rf)-IF
69
it is any frequency other than the selected radio frequency carrier that ( if allowed to enter a receiver and mix with local oscillator ) will produce a cross product frequency that is equal to Intermediate Frequency
Image Frequency:
f(image) = f(rf) + 2(IF) ... FOR HIGH SIDE INJECTION
f(image) = f(rf) - 2(IF) ... FOR LOW SIDE INJECTION
70
it is the numerical measure of the ability of a pre-selector to "reject the image frequency" ; the higher the IFRR the BETTER
Image Frequency Rejection Ratio:
IFRR = sqrt 1 + (Q^2) (P^2)
IFRR = 20 log (sqrt 1 + (Q^2) (P^2) )
p= f(image)/f(rf) - f(rf)/f(image)
71
also called as muting circuit , used to keep the receiver audio turned off until RF signal appears at the receiver input ( used to quiet a receiver in the absence of a received signal ) .
Squelch Circuit
72
It is form of amplitude modulation in which the carrier is totally suppressed
Double Sideband Suppressed Carrier (A3J)
73
it is a circuit that generates a DSB Signal , suppressing the carrier and leaving only the sum and difference frequencies at the output. the output of a balanced modulator can be further processed by filters or phase-shifting circuitry to eliminate one of the sidebands, resulting in an SSB Signal.
Balanced Modulator
74
DSBSC Equation :
V(t)= (mVc/2)cos(wc-wm)t - (mVc/2)cos(wc+wm)t
75
DSBSC Current and Voltage :
```
IT = IC(M/sqrt2)
VT = VC(M/sqrt2)
```
76
DSBSC Power :
```
PT = 2PSB
PT = PC(M^2/2)
```
77
Power Saving for DSBSC :
%PS = (P(am)-P(dsbsc)/P(am)) x 100%
78
DSBSC Bandwidth Requirements:
B(dsbsc) = 2fmax
79
it is a form of amplitude modulation in which carrier is totally suppressed and one of the sideband removed
Single Sideband Suppressed Carrier (J3E)
80
SSBSC Equation :
```
V(t) = - (mVc/2)cos(wc+wm)t
V(t) = +(mVc/2)cos(wc-wm)t
```
81
SSBSC Current and Voltage:
```
IT = IC(M/2)
VT = VC(M/2)
```
82
SSBSC Power :
```
PT = PSB
PT = PC(M^2/4)
```
83
Power Saving for SSBSC :
%PS = (P(am)-P(ssbsc)/P(am)) x 100%
84
it is the RMS power developed at the crest of the modulation envelop . the power of an SSBSC signal is usually expressed in PEP
Peak Envelop Power ( PEP ) :
PEP = VRMS^2/RL
P(ave) = PEP/3
P(ave) = PEP/4
85
SSBSC Bandwidth Requirements:
B(ssbsc) = fmax
86
SSBSC Generation :
- Filter Method
- Phase Shift Method
- Third ( Weaver ) Method
87
it is the simplest method of generating SSB. it uses LC , crystal , ceramic , or mechanical filters to eliminate one of the sidebands of the SSB. It is easy to construct , however , filter response are not idea, so the sideband may be cut or there will be still a small portion of the other sideband . it consist fo one balanced modulator
Filter Method
88
it make use of the two balanced modulators and two phase shifters . it reduces the bulkiness of the filters and its inherent disadvantages.
Phase Shift Method
89
it retains the advantages of the phase shift method whithout the disadvantages of the AF phase shift method . it consist of four balanced modulators.
Third ( Weaver ) Method
90
it is a form of amplitude modulation in which the carrier is transmitted at full power but only one of the sidebands is transmitted.
Single Sideband Full Carrier (H3E)
91
it is also known as single sideband reinserted carrier , and it is a form of amplitude modulation in which one sideband is totally removed and the carrier voltage is reduced to approximately 10% of its unmodulated amplitude.
Single Sideband Reduced Carrier (R3E)
92
usually work by filtering a DSBSC signal to remove the unwanted sideband, then using a mixer to move the signal to the operating frequency
SSB Transmitters
93
require a beat frequency oscillator (BFO) to reinsert the carrier, and generally use the product detectors.
SSB Receivers
94
it is a form of amplitude modulation in which a single carrier frequency is independently modulated by two different modulating signals ( ie. contains different information for each sideband )
Independent Sideband(ISB) - (B8E)
95
it is a form of amplitude modulation in which the carrier and one complete sideband are transmitted , but only part of the second sideband is transmitted.
is used for the picture portion of a commercial television broadcasting signal.
Vestigial Sideband(VSB) - (C3F)
96
Advantages of Single Sideband Transmission:
- Power Conservation
- Bandwidth Conservation
- Selective Fading
- Noise Reduction
97
Disadvantages of Single Sideband Transmission:
-Complex Receivers
:envelope detection cannot be used unless the carrier is generated
-Tuning Difficulties
:SSB receivers require more complex and precise tuning than conventional AM receivers
98
the efficiency of an AM Signal is improved by
Suppressing the carrier , but the demodulation making more difficult.
99
it is a type of analog modulation in which the angle sinusoidal reference function is varied in accordance with a modulation signal.
Angle Modulation:
- Frequency Modulation
- Phase Modulation
100
it is modulation technique invented by Edwin Armstrong where the information signal is analog and the frequency of the carrier is varried proportional to the information signal.
Frequency Modulation (FM)
101
Standard FM Range :
88Mhz - 108 Mhz
102
Standard FM Intermediate Frequency
the Standard IF Frequency for FM is 10.7 Mhz
103
Standard FM Equation :
v(t) = vc(cos) ( wct + (delta/fm) ( sin(wmt) )
104
it is the relative displacement of the carrier frequency in respect to its unmodulated value. it is the amount of change in carrier frequency produced by the modulating signal.
Frequency Deviation:
delta = kf x vm
```
kf = frequency deviation constant , hz/v
vm= modulating signal peak voltage , v
```
105
it is the ratio of deviation and the modulating signal frequency. it determines the number of significant pairs of sidebands in an FM signals
FM Modulating Index:
| m=delta/fm
106
it is the worst case modulation index and is equal to the maximum peak frequency deviation divided by the maximum modulating signal frequency
Deviation Ratio:
| DR = delta(max) / fm(max)
107
it is the ratio of the frequency deviation actually produced to the maximum frequency deviation allowed by the law stated in percent form
FM Percent Modulation:
| %m = (delta/delta(max)) x 100%
108
it is the peak to peak frequency deviation
Carrier Swing :
| CS = 2(delta)
109
it is a rule which is an approximation and gives transmission bandwidths that are slightly narrower than the bandwidths. it defines a bandwidth that includes approximately 98% of the total power in the modulated wave.
Carson's Rule:
| B(carson) = 2 (delta + fm)
110
an FM system with relatively low modulation index (m<0.25)
```
Narrowband FM (NBFM):
B(NBFM) = 2 x fm
```
111
an FM system witg relatively high modulation index (m>100)
```
Wideband FM (WBFM):
B(WBFM) = 2 x delta
```
112
in FM the Maximum Frequency Deviation is
75khz with maximum modulating-signal frequency of 15khz
113
FM Generation :
```
-Direct Method
Reactance Modulator
Varactor Diode Modulator
-Indirect Method
Armstrong Modulator
```
114
it is an FM Generation method in which the output is already an FM signal
Direct Method
115
it has a reactance tube that presents inductive or capacitive reactance is connected to the tank circuit of the oscillator. the variation of the reactance would cause the oscillator frequency to vary in accordance with the modulating signal thereby creating a direct generation of FM.
Reactance Modulator
116
it is an FM generator utilizing a voltage-variable capacitor diode. a varactor diode or varicap is a specially constructed diode whose internal capacitance is enhanced when reversed biased, and by varying the reverse-bias voltage , the capacitance of the diode can be adjusted. VCOs are FM circuits in which continuous variable changes in frequency are provided by the varactor diode
Varactor Diode Modulator
capacitance of varactor diode
c=co/sqrt (1 + 2 x V)
117
it is an FM Generation method wherein the signal is first phase-modulated before producing the FM signal. it is the most widely used method, since PM is cheaper to produce than FM
Indirect Method
118
Differentiator followed by FM modulator
PM Modulator
119
FM Demodulator followed by an Integrator
PM Demodulator
120
Integrator followed by a PM modulator
FM Modulator
121
PM Demodulator followed by a differentiator
FM Demodulator
122
FM Detection :
- Slope Detector
- Round-Travis Detector
- Foster-Seeley Discriminator
- Ratio Detector
- Quadrature Detector
- Phase Lockked Loop Detector
123
it is an FM Detection Method in which a frequency-modulated signal is fed to a circuit that is tuned to received the signal in the slope of response curve,
the fm signal is converted into am
Slope Detector
124
it is an FM detector using two slope detectors. the output is taken from across the series combination of the two loads, so that it is the sum of the two inputs
Round-Travis Detector
125
it is also known as the center tapped or phase discriminator. it is an FM detection method wherein changes in the magnitude of the input signal will give rise to the amplitude changes in the resulting output voltage
Foster-Seeley Discriminator
126
it is a variation of the Foster-Seeley Discriminator which includes an amplitude limiter which improves the limiting action. its output through, is one-half that of the Foster-Seeley Discriminator
Ratio Detector
127
it is also known as COINCIDENCE DETECTOR. it extracts the original information signal from the composite IF waveform by multiplying two quadrature signals.
Quadrature Detector
128
it is the simplest and easiest to understand FM Detector. it is a closed-loop feedback control system in which either the frequency or phase of the feedback signal is the parameter of interest rather than the magnitude of the signal's voltage or current. the PLL frequency demodulator requires no tuned circuits and automatically compensates for changes in the carrier frequency due to instability in the transmit oscillator
Phase Locked Loop
129
Phase Locked Loop Blocks
- Phase Detector
- Loop Filter
- Voltage-Controlled Oscillator
130
it is a nonlinear device with two input signals ; an externally generated frequency and VCO output Frequency. the output of the phase comparator is the sum and difference frequencies of the input and the VCO output
Phase Detector
131
it helps establish the proper transient response and the required filtering
Loop Filter
132
it is an oscillator with stable frequency of oscillation that depends on the external bias voltage
Voltage-Controlled Oscillator (VCO)
133
PLL Loop Operation States:
- Free Running State
- Capture State
- Lock State
134
it is the PLL state when there is no external input frequency or the feedback loop is open
Free-running State
135
it is the state when the PLL is in the process of acquiring frequency lock
Capture State
136
it is the state when the VCO output frequency is locked onto ( equal to ) the frequency of the external input signal
Lock State
137
PLL Key Parameters:
- lock range
- hold-in range
- capture range
- pull-in range
138
it is also known as tracking range, which is defined as the range of frequencies in the vicinity of the VCO's natural frequency over which the PLL can maintain lock with an input signal
Lock Range
139
it is the lock range expressed as peak value
Hold-in Range
140
it is also known as acquisition range, which is defined as the band of frequencies in the vicinity of the natural frequency where the PLL can establish or acquire lock with an input signal
Capture Range
141
it is the capture range expressed as a peak value
Pull-in Range
142
is the VCO's output frequency when the PLL is not locked
Preset or Natural Free-Running Frequency
143
is the time required to achieved lock
Acquisition Time
144
Emphasis Networks:
- Pre-Emphasis Network
| - De-Emphasis Network
145
it uses a high pass filter, wherein the high-frequency modulating signals are emphasized or boosted in amplitude in the transmitter prior to performing modulation. high frequencies are amplified further in order to protect them. it is used in transmitter circuits
Pre-Emphasis Network
146
it uses low pass filter, and it is just the reciprocal of pre emphasis that restores the original amplitude-versus frequency characteristics to the information signals. it is used in receiver circuits
De-Emphasis Network
147
the standard cut-off frequency used for the filters in the emphasis network is
2122 Hz
148
it is the inherent ability of an FM receiver to diminish the effects of interfering signals (ie. it is the ability of an FM receiver to differentiate between two signals received at the same frequency)
Capture Effect
149
it is the noise-reduction effect that occurs with strong FM Signals
Threshold Effect
150
it is also known as clipper, which is used to remove sporadic high-amplitude noise transients of short duration, such as impulse noise in the audio section of a receiver.
it is a special circuit that removes the unwanted amplitude variations since with FM, the information is contained in frequency variations
Limiter
151
It is a modulation technique where the information signals is analog and the phase of the carrier is varried proportional to the information signal . it is similar to FM with a phase shift of 90 degrees
Phase Modulation
152
Standard PM Equation:
v(t)pm= vc cos( wct + deltacos(wmt) )
153
it is the relative angular displacement (shift) of the carrier phase in radians in respect to the reference phase
Phase Deviation : (delta)
| delta = kp x Vm
154
PM Modulation Index :
M = delta
155
in PM
the modulation index is directly proportional to the amplitude of the modulating signal and independent of its frequency.
156
in FM
the modulation index is directly proportional to the amplitude of the modulating signal and inversely proportional to its frequency
157
advantages of angle modulation :
- Noise Immunity because of limitters
- Capture Effect
- Power Utilization and Efficiency
158
disadvantages of angle modulation
- bandwidth is much wider than AM
| - circuit complexity and cost
