Receiver sensitivity determinants In a superheterodyne receiver, which factors primarily determine the sensitivity (i.e., the minimum input required for a specified output and S/N)?

Introduction / Context:
Sensitivity indicates how weak a signal a receiver can detect at a specified output and signal-to-noise ratio. It depends on both gain distribution and noise performance across stages, as summarized by Friis’s formula for cascaded noise figure.

Given Data / Assumptions:

• Superheterodyne receiver with RF amplifier, mixer, IF strip, detector.
• Target is a standard output level and S/N at the demodulator or audio output.
• Wideband thermal and device noises are present.

Concept / Approach:
Overall sensitivity improves with adequate front-end gain that suppresses contributions of noisy subsequent stages, and with low noise figure in the first stage. IF gain also matters because the detector needs sufficient input. Therefore, both gains (RF and IF) and noise figure together define sensitivity.

Step-by-Step Solution:
Apply Friis’s formula: system noise figure is dominated by the first active stage’s NF and its gain.Ensure enough IF gain to reach the detector’s required drive without adding excessive noise.Conclude that sensitivity is determined by RF/IF gains and overall noise figure.

Verification / Alternative check:
Manufacturer datasheets state sensitivity together with IF gain and front-end NF; improving any of these (to a point) enhances minimum discernible signal.

Why Other Options Are Wrong:

• Single-stage answers (RF-only or IF-only) ignore the cascaded nature.
• Noise figure alone does not guarantee adequate detector drive without gain.
• Antenna impedance matters for matching but is not the dominant determinant in isolation.

Common Pitfalls:

• Overemphasizing IF gain while neglecting front-end NF.
• Forgetting that too much gain can cause overload; sensitivity must be paired with linearity.

Final Answer:
All of the above acting together (RF/IF gains and noise figure)