A superheterodyne receiver with an IF of 450 kHz is tuned to a signal at 1200 kHz. The image frequency is

Answer: Option D

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

Intermediate Frequency (IF): The intermediate frequency (IF) is a fixed frequency to which the received radio frequency (RF) signal is converted in a superheterodyne receiver. This allows for efficient amplification and filtering of the signal before demodulation.

Image Frequency: The image frequency is an unwanted signal that can also produce the same IF frequency as the desired signal. It occurs because the mixer in a superheterodyne receiver is essentially a non-linear device which produces sum and difference frequencies. The image frequency is always offset from the desired signal frequency by twice the IF.

Calculating Image Frequency: In this question, the desired RF signal is at 1200 kHz, and the IF is 450 kHz. The image frequency (f_image) can be calculated using the following formula:

f_image = f_RF ± 2 * f_IF

Where:
f_RF is the radio frequency (1200 kHz)
f_IF is the intermediate frequency (450 kHz)

Using the formula:

f_image = 1200 kHz + 2 * 450 kHz = 2100 kHz
or
f_image = 1200 kHz - 2 * 450 kHz = 300 kHz (This is not among the options)

Therefore, the image frequency is 2100 kHz (Option D).