Question
Which of the following choices is a good reason for selecting a high IF for a superheterodyne HF or VHF communications receiver?
Answer Options
- A) Fewer components in the receiver
- B) Reduced drift
- C) Easier for front-end circuitry to eliminate image responses
- D) Improved receiver noise figure
Correct Answer: C
Explanation
In a superheterodyne receiver, the Intermediate Frequency (IF) is the fixed frequency to which the desired input signal is mixed down. The selection of the IF frequency is a major design choice that impacts several aspects of the receiver’s performance, especially its ability to reject unwanted signals.
Selecting a high IF frequency is a good design choice because it makes it easier for the front-end circuitry to eliminate image responses. The ‘image’ is an unwanted signal that is twice the IF frequency away from the desired signal. A higher IF means the image frequency is located farther away from the desired signal, allowing simple, non-critical band-pass filtering in the RF front end to easily attenuate it before it reaches the mixer.
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