Question

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

• A. $RC=1/f$
• B. $RC<1/f$
• C. $RC\ge 1/f$
• D. $RC>>1/f$

Answer 1

The correct option is D $RC>>1/f$

In demodulation, high frequency carrier wave is filtered out to get signal wave. For it we use capacitance in parallel which absorbs high frequency component of the import modulated signal. So reactance of $C$ should be small.
$\Rightarrow \frac{1}{\omega C}<<R$ or $\frac{1}{2\pi fC}\le R$

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