Broadcast superheterodyne receiver principle: Which of the following statements correctly describe the operation of a broadcast superheterodyne receiver?

Introduction / Context:
Broadcast superheterodyne receivers are the most common radio architecture, using frequency conversion to simplify selectivity and amplification.

Given Data / Assumptions:

• Receiver tuned frequency f_s.
• Local oscillator frequency f_lo typically = f_s + IF.
• Mixer requires inputs of both f_s and f_lo.

Concept / Approach:

The mixer stage combines the incoming RF signal with the local oscillator signal, producing sum and difference frequencies. To achieve proper conversion, the RF input must be tuned to the desired signal frequency f_s.

Step-by-Step Solution:

Verification / Alternative check:

Superheterodyne block diagrams confirm that the mixer input is always tuned to the signal frequency, while the LO is offset by IF.

Why Other Options Are Wrong:

• Local oscillator below signal: uncommon for broadcast receivers.
• LO = 2*IF: not a general rule.
• RF amp above carrier by a few kHz: incorrect.

Common Pitfalls:

• Confusing LO frequency placement (above vs. below signal).

Final Answer:

The mixer input must be tuned to the signal frequency.