Subelement F: Receivers— Topic 41: Receiver Theory
Question 3-41F5
Element 3 (GROL)Which stage of a receiver primarily establishes its noise figure?
Explanation
The RF (Radio Frequency) stage is the first active component to process the extremely weak signal from the antenna. The noise figure of a receiver is primarily determined by this initial stage because any noise added here is amplified by all subsequent stages (mixer, IF amplifier, audio amplifier).
While later stages like the IF strip and audio stage also introduce noise, their contributions are effectively *reduced* by the gain of the preceding stages. This means the noise from the RF stage, which amplifies both the signal and its own inherent noise, sets the fundamental noise floor for the entire receiver. The local oscillator generates a frequency but doesn't primarily establish the system's noise figure. Therefore, a low-noise RF amplifier is critical for good receiver sensitivity.
Related Questions
3-41F3 What is the term used to refer to a reduction in receiver sensitivity caused by unwanted high-level adjacent channel signals?3-41F4 What is meant by the term noise figure of a communications receiver?3-41F6 What is the term for the ratio between the largest tolerable receiver input signal and the minimum discernible signal?3-42F1 How can selectivity be achieved in the front-end circuitry of a communications receiver?3-42F2 What is the primary purpose of an RF amplifier in a receiver?