AdvancedA-006-002-008
In a superheterodyne receiver without an RF amplifier, the input to the mixer stage has a variable capacitor in parallel with an inductance. The variable capacitor is for:
C
Answer
Propagation and operating practice
Type
A
tuning the beat-frequency oscillator
B
tuning both the antenna and the beat-frequency oscillator
C
tuning the receiver preselector to the reception frequency
D
tuning both the antenna and the local oscillator
Answer Notes
In a superheterodyne receiver lacking a dedicated RF amplifier, the antenna connects directly to the input of the mixer stage through an LC (inductor-capacitor) circuit. This LC circuit acts as a tuned bandpass filter, commonly called a preselector.
The variable capacitor in this preselector circuit is used to tune the resonant frequency to match the desired reception frequency. This ensures that only the frequency band of interest reaches the mixer, rejecting out-of-band signals and preventing unwanted image frequencies from causing interference. It does not tune the local oscillator or the BFO.
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In a superheterodyne receiver, a stage before the IF amplifier has a variable capacitor in parallel with a trimmer capacitor and an inductance. The variable capacitor is for:
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What receiver stage combines a 14.25-MHz input signal with a 13.795-MHz oscillator signal to produce a 455-kHz intermediate frequency (IF) signal?