Limitations of the tuned-radio-frequency (TRF) receiver Which of the following is a recognized drawback of the TRF architecture when compared to the superheterodyne?

Difficulty: Easy

Correct Answer: All of the above

Explanation:


Introduction / Context:
Before the superheterodyne, the TRF receiver used multiple cascaded RF tuned stages at the signal frequency. While workable for narrow ranges, TRF is fundamentally limited for wide tuning and stringent selectivity requirements.



Given Data / Assumptions:

  • TRF uses several RF amplifiers all tuned to the desired RF channel.
  • Bandwidth and gain must be consistent over a large tuning span.
  • Oscillations and tracking errors are practical concerns.



Concept / Approach:
Because each RF stage must track the others as the tuning knob moves, small misalignments or component tolerances degrade selectivity. High gain at RF can cause instability (oscillation). Also, the achievable bandwidth (shape factor) varies with frequency, reducing adjacent-channel rejection.



Step-by-Step Solution:
Assess stability → many high-Q RF stages in cascade increase likelihood of oscillation.Assess selectivity → tracking multiple resonators compromises skirt selectivity across the band.Assess bandwidth → passband changes with tuned frequency because LC reactances change and coupling is not constant.



Verification / Alternative check:
Historical receiver literature shows the superheterodyne superseded TRF largely due to these issues, especially for broadcast bands and beyond.



Why Other Options Are Wrong:

  • Each listed drawback is real; hence “none of the above” is incorrect.
  • Claiming parity with superhet ignores the architectural advantages of a fixed IF.



Common Pitfalls:

  • Underestimating the difficulty of multi-circuit tracking at RF.
  • Confusing image problems (a superhet issue) with TRF’s bandwidth inconsistency; both architectures have different challenges.



Final Answer:
All of the above


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