1. FM Generation
A. D. Patel Institute Of Technology
EC :- Sem V Present By :- Pratik Makadia
(130010111017)
19 October
2015
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2. FM SIGNAL GENERATION
β’ They are two basic methods of generating frequency- Modulated signals
1. Direct Method
2. Indirect Method
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3. DIRECT FM
ππ = ππ + π π π(π‘)
β’ In a direct FM system the instantaneous frequency is directly varied with the
information signal. To vary the frequency of the carrier is to use an
Oscillator whose resonant frequency is determined by components that can
be varied. The oscillator frequency is thus changed by the modulating signal
amplitude.
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5. FM Generation
β’ FM generation is quite easy. All that is needed is a linear voltage-to-frequency
converter.
β’ If a voltage-controlled capacitor is placed in the feedback loop of an
oscillator and the modulation signal is applied across this capacitor, then the
oscillator will change in frequency and the resulting output signal is an FM
signal.
β’ The LM 566C to generate the FM signal.
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6. Fig:- FM generation using the LM 566C. The LM 386 drives the LED
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8. NOISE IN FM SIGNAL
1. Noise is essentially amplitude variations. An FM signal, on the other hand,
has a constant carrier amplitude.
2. Because of this, FM receivers contain limiter circuits that restrict the
amplitude of the received signal.
3. Any amplitude variations occurring on the FM signal are effectively clipped
off. This does not hurt the information content of the FM signal. Because
of the clipping action of the limiter circuits, noise is almost completely
eliminated.
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