Question

The image channel selectivity of super heterodyne receiver depends upon ________.

• A. IF amplifiers only
• B. RF and IF amplifiers only
• C. Pre selector, RF and IF amplifiers
• D. Pre selector and RF amplifiers

Hint:

Image rejection in superheterodyne receivers needs filtering at multiple stages: pre-selector, RF amp, and IF stage.

Answer 1

The Correct Option is C

In a superheterodyne receiver, image frequency rejection is critical for proper demodulation. The image frequency is: \[ f_{image} = f_s + 2f_{IF} \] To suppress signals at the image frequency, the system relies on:
- Pre-selector filters before RF amplification to attenuate out-of-band signals including image frequencies.
- RF amplifiers which provide initial gain and should be selective enough.
- IF amplifiers, though tuned to a fixed IF frequency, still contribute to selectivity.
Thus, optimal image frequency rejection is achieved using a combination of Pre-selector + RF amplifiers + IF amplifiers.