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Which of the following statements about radio receivers is false?

Difficulty: Medium

Correct Answer: Variable sensitivity is used to improve selectivity

Explanation:


Introduction / Context:
Receiver design includes multiple techniques to improve selectivity, sensitivity, and image rejection. However, some statements can be misleading if the functions of these features are not understood correctly.


Given Data / Assumptions:

  • Double conversion improves performance.
  • Variable sensitivity relates to gain control.
  • Selective fading occurs due to multipath propagation.


Concept / Approach:
Double conversion is a known method to improve both selectivity and image rejection. Variable sensitivity, however, does not improve selectivity; it adjusts receiver gain to handle strong or weak signals. Hence, the claim that variable sensitivity improves selectivity is false.


Step-by-Step Solution:

Selectivity is improved by IF filters, not sensitivity control.Double conversion → better image rejection and narrower IF bandwidth.Variable sensitivity → prevents overload on strong signals but does not affect selectivity.Selective fading is mitigated by diversity reception, not sensitivity adjustment.


Verification / Alternative check:

Textbooks confirm: sensitivity control = RF gain control, not selectivity improvement.


Why Other Options Are Wrong:

Other statements about double conversion and fading elimination are correct in their contexts.


Common Pitfalls:

Confusing sensitivity with selectivity. They are different performance measures.


Final Answer:

Variable sensitivity is used to improve selectivity
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