The image frequency of a superheterodyne receiver

Solution (By Examveda Team)

Superheterodyne Receiver: A superheterodyne receiver is a type of radio receiver that uses a mixer to convert a radio frequency (RF) signal to a lower intermediate frequency (IF) signal. This IF signal is then amplified and filtered before being demodulated to extract the audio signal.

Image Frequency: The image frequency is an unwanted signal that can interfere with the desired signal in a superheterodyne receiver. It is a frequency that, after mixing with the local oscillator (LO) frequency, produces the same IF frequency as the desired signal.

Correct Answer: A
The image frequency is created within the receiver itself. The mixer in the superheterodyne receiver combines the incoming RF signal with the LO signal. Both the desired RF signal and the image frequency, when mixed with the LO signal, produce the same IF frequency. This is because the mixer is a non-linear device that produces sum and difference frequencies. Therefore, two different RF signals can create the same IF frequency.

Why other options are incorrect:
Option B: Insufficient adjacent channel rejection is a separate issue related to the receiver's ability to discriminate between closely spaced channels. It's not directly related to the image frequency's generation.
Option C: The IF tuned circuits are designed to select and amplify the desired IF signal. However, because the image frequency produces the same IF frequency, it passes through these circuits along with the desired signal. Therefore, image frequency rejection depends on prior stages rather than just IF filters.
Option D: The image frequency is directly dependent on the frequency to which the receiver is tuned. The image frequency is separated from the desired signal by twice the IF frequency. If the desired signal changes, then the image frequency also changes.