Consider the frequency demodulation scheme in Figure in which
Consider the frequency demodulation scheme in Figure in which the incoming FM signal s (t) is passed through a delay line that produces a phase-shift of p/2 radians at the carrier frequency A?c. The delay-line output is subtracted from the incoming FM signal, and the resulting composite signal is then envelope-detected. This demodulator finds application in demodulating microwave FM signals. Assuming that s (t) = Ac cos (2pA?ct) + Ă sin (2pA?mt) analyze the operation of this demodulator when the modulation index Ă is less then unity and the delay T produced by the delay line is sufficiently small to justify making the approximations cos (2pA?mT) = 1 and sin (2pA?mt) = 2pA?mt
