If an amplitude modulated wave 10[1 + 0.6 cos 2π10³t] cos2π.10⁶ .t is to be detected by a linear diode detector, then the time constant will be:

Question

Question

This question was previously asked in

UGC NET Paper 2: Electronic Science 3rd Dec 2021 Shift 2

Answer 1

Concept:

For envelope detector, the time constant must satisfy the following relation:

\(RC \le \frac{1}{{{\omega _m}}}\left[ {\frac{{\sqrt {1 - {μ^2}} }}{μ}\;} \right]\) ---(1)

For the good performance of the envelope detector:

\(\frac{1}{\omega_c}<<RC<<\frac{1}{\omega_m}\)

Application:

Given:

\(\omega_m\) = 2π103 rad/sec

modulation index (μ) = 0.6

From (1), we get

\(RC \le \frac{1}{{{2\pi \times 10^3}}}\left[ {\frac{{\sqrt {1 - {0.6^2}} }}{0.6}\;} \right]\)

=0.21 msec