Question

In a broadcast superheterodyne receiver, the ____________

(a) Local oscillator always operates below the frequency of transmitted signal

(b) Input of mixer must be tuned to the signal frequency

(c) Local oscillator frequency should be double than that of IF

(d) RF amplifier normally works at 455 KHz above the carrier frequency

The question was asked during an online interview.

This intriguing question originated from Noise for AM Wave topic in division Noise of Analog Communications

Answer 1

Correct choice is (b) Input of mixer must be tuned to the signal frequency

The best I can explain: For a superheterodyne receiver, one of the inputs of the mixer must be tuned to the signal frequency and another input is of the local oscillator frequency. Tuning means that the circuit works for that one signal frequency only.