Superheterodyne receiver image frequency: In a superheterodyne receiver with an intermediate frequency (IF) of 455 kHz, if the tuned signal frequency is 1200 kHz, what will be the corresponding image frequency?

Difficulty: Medium

Correct Answer: 2110 kHz

Explanation:


Introduction / Context:
Image frequency is a key concept in superheterodyne receivers. It represents an undesired frequency that can also mix with the local oscillator to produce the same IF as the desired signal, leading to interference unless filtered.


Given Data / Assumptions:

  • Intermediate frequency (IF) = 455 kHz.
  • Signal frequency tuned (f_s) = 1200 kHz.
  • Local oscillator frequency (f_lo) = f_s + IF = 1200 + 455 = 1655 kHz.


Concept / Approach:

The image frequency f_i is given by: f_i = f_lo + IF = f_s + 2IF.


Step-by-Step Solution:

Compute f_lo = f_s + IF = 1200 + 455 = 1655 kHz.Image frequency f_i = f_lo + IF = 1655 + 455 = 2110 kHz.


Verification / Alternative check:

Another formula: f_i = f_s + 2IF = 1200 + 910 = 2110 kHz, confirming the result.


Why Other Options Are Wrong:

  • 1655 kHz: this is the local oscillator frequency, not the image.
  • 745 kHz or 910 kHz: irrelevant lower frequencies.
  • 2400 kHz: not related by standard image formula.


Common Pitfalls:

  • Confusing LO frequency with image frequency.
  • Forgetting that image is separated by 2*IF from the desired signal.


Final Answer:

2110 kHz.

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