Question

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

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

Answer 1

Answer: (D)

$RC > >\frac{1}{ f }$

Answer 2

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 as shown. 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.