Angular Modulation Flashcards
A modulation technique wherein the amplitude of the carrier is kept constant while the angle or the argument of the carrier is varied in accordance with the intelligence signal
Angular Modulation
2 kinds of angular modulation
Frequency Modulation and Phase Modulation
a form of angle modulation where the frequency of the carrier is varied in accordance with the instantaneous value of the intelligence signal.
Frequency Modulation
the amount of change in the carrier frequency produced by the modulating signal.
Frequency Deviation
Frequency Deviation
the amount of change in the carrier frequency produced by the
modulating signal.
In FM, the intelligence amplitude, Em, determines the
amount of carrier frequency change
In FM, the intelligence frequency, fm, determines the
rate of change of the carrier frequency
Ratio of the frequency deviation over modulating frequency
Modulation Index (FM)
Modulation Index (FM)
Ratio of the frequency deviation over modulating frequency
Whenever the maximum allowable frequency deviation and the maximum modulating frequency are used in computing the modulation index.
Deviation Ratio
Expression of the worst case modulation index.
Deviation Ratio
FCC Rules
FM
max carrier deviation = 75 kHz
max intelligence f = 15 kHz
FCC Rules
TV Sound
max carrier deviation = 25 kHz
max intelligence f = 15 kHz
FCC Rules
Public Safety Services
max carrier deviation = 5 kHz
max intelligence f = 3 kHz
FCC Rules
Amateur Band Radio
max carrier deviation = 3 kHz
max intelligence f = 3 kHz
Advantages of FM over AM
- better noise immunity
- rejection of interfering signals because of “capture effect”
- better transmitter efficiency
Disadvantages of FM over AM
- large bandwidth
- more complex and expensive circuits
- reception is limited
boosts the high audio frequencies in modulation at the transmitter, used to improve the signal-to-noise ratio.
Pre-Emphasis Circuit
attenuates the high audio frequencies (at the receiver) by the same amount that they were boosted
De-Emphasis Circuita form of angle modulation where the phase of the carrier is varied in
accordance with the instantaneous value of the modulating signal
a form of angle modulation where the phase of the carrier is varied in accordance with the instantaneous value of the modulating signal
Phase Modulation
