In a broadcast superheterodyne receiver, the

Superheterodyne Receiver: A superheterodyne receiver is a type of radio receiver that uses a mixer to convert the radio frequency (RF) signal to a lower, intermediate frequency (IF). This process simplifies the amplification and filtering of the signal, improving selectivity and sensitivity.

Intermediate Frequency (IF): The IF is a fixed frequency to which all received signals are converted regardless of their original RF frequency. A common IF frequency is 455 kHz.

Correct Answer: B
Explanation: The mixer in a superheterodyne receiver requires two inputs: the incoming RF signal and the signal from the local oscillator (LO). The mixer combines these two signals, resulting in a difference frequency which is the IF. To ensure that the RF signal is properly mixed, the mixer input must be tuned to the signal frequency. This tuning is typically accomplished using a tunable RF amplifier circuit.

Why other options are incorrect:
Option A: The local oscillator (LO) frequency is typically above the signal frequency. The difference between the LO frequency and the signal frequency produces the IF. If the LO was below, a negative IF would result, which is impractical.

Option C: The LO frequency is not normally double the IF. It's designed to be either higher or lower than the incoming signal frequency by an amount equal to the IF frequency.

Option D: The RF amplifier operates at the signal frequency, not 455 kHz above it. The 455 kHz (or other IF) frequency is created after the RF signal passes through the mixer and is down-converted.