Fm & Pm Modulation

Topics: Modulation, Frequency modulation, Amplitude modulation Pages: 1 (255 words) Published: April 12, 2013
Introduction
Angle modulation consist of :
* FM (Frequency Modulation)
* PM (Phase Modulation)
FM (Frequency Modulation)
The need for modulation arises because the range of frequencies contained in a baseband signal is not, in general, the same as the range of frequencies which can be transmitted by the communications channel. * AM – Amplitude Modulation

Medium wave (300 kHz to 3 Mhz) , short wave (3-30 Mhz)
* FM – Frequency Modulation
VHF (30-300 MHz)
FM is the process of varying the frequency of a carrier wave in proportion to a modulating signal. The amplitude of the carrier is constant while its frequency and rate of changes varied by the modulating signal FM Modulator

FM Modulator
FM Signal
FM Signal

Figure 1 : Frequency Modulated Signal
The FM Modulator received two signals, the information signal from an external source and the carrier signal from an external source and the carrier signal from a built in oscillator. The modulator circuit combines the two signals producing a FM signal which is passed on to the transmission medium. PM (Phase Modulation)

Phase Modulation is a system in which the phase of the carrier signal is varied by the information signal. The amplitude of the carrier is kept constant : The phase ∅ in the equation v = VC cos ( C + ∅ ) is varied, so that its magnitude is proportional to instantaneous amplitude of the modulating signal. With PM, the maximum frequency deviation ∅, occurs during the zero accrosing of the modulating signal, that is the f is proportional to the slope or first derivative of the modulating signal.
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