Question

Given below is a circuit diagram of an $AM$ demodulator. For good demodulation of $AM$ signal of carrier frequency $ f, $ the value of $RC$ should be

• A. $ RC=\frac{1}{f} $
• B. $ RC<\frac{1}{f} $
• C. $ RC\ge \frac{1}{f} $
• D. $ RC>>\frac{1}{f} $

Answer 1

Answer: (D)

From the modulated signal, we can demodulate or detect the modulating or message signal by using a diode and a suitable capacitor filter. The $AM$ signal given to the input of the circuit appears at the output of the diode as a rectified wave. For good demodulation of $AM$ signal the value of $R C$ (which is a time-constant) is chosen such that
$\frac{1}{f} < < R C $ or $ R C > > \frac{1}{f}$
where $f$ is the frequency of the carrier signal.