FCC Exam Question: 6A474

What is the IF of a superheterodyne receiver receiving on 1000 kHz and the mixing oscillator is tuned to1500 kHz?

A. 500 kHz
B. 2500 kHz
C. 2000 kHz
D. None of the above
Correct Answer: A

Explanation: In a superheterodyne receiver, the Intermediate Frequency (IF) is generated by mixing the incoming Radio Frequency (RF) signal with a signal from a Local Oscillator (LO). This mixing process produces sum and difference frequencies. The IF is typically chosen as the difference frequency because it allows for stable amplification and filtering at a fixed frequency, regardless of the tuned RF frequency. In this case: RF signal = 1000 kHz Local Oscillator (LO) frequency = 1500 kHz The IF is the absolute difference between the LO and RF frequencies: IF = |LO - RF| IF = |1500 kHz - 1000 kHz| IF = 500 kHz Therefore, option A is correct. Option B (2500 kHz) would be the sum frequency (1500 kHz + 1000 kHz), which is also a product of mixing but not the intended IF in most superheterodyne designs. Option C (2000 kHz) is not a result of this specific mixing process.

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Includes Elements 1, 3, 6, 7R, 8, and 9.