Receivers and Transmitters Flashcards
7 cards from real GROL practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
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What is the primary purpose of the IF (intermediate frequency) stage in a superheterodyne receiver?
Answer: To provide fixed-frequency amplification and selectivity
The IF stage amplifies and filters the signal at a fixed frequency after mixing, making high-quality filtering practical regardless of the tuned frequency.
In a superheterodyne receiver, the local oscillator frequency is typically offset from the incoming RF signal by:
Answer: The intermediate frequency (IF)
Mixing the RF signal with the local oscillator (offset by the IF) produces a difference frequency equal to the IF, which is then amplified and filtered.
What is the image frequency in a superheterodyne receiver?
Answer: A second RF frequency separated from the desired signal by twice the IF that also produces an IF output when mixed
The image frequency is separated from the desired signal by 2 × IF; it mixes with the local oscillator to produce an output at the IF just like the desired signal.
Automatic Gain Control (AGC) in a receiver is designed to:
Answer: Maintain a relatively constant audio output level across a wide range of signal strengths
AGC reduces the gain of RF and IF amplifier stages when strong signals are received, preventing overloading while keeping weak signals audible.
The noise figure of a receiver is a measure of:
Answer: How much noise the receiver itself adds relative to the thermal noise floor
Noise figure (in dB) quantifies the degradation of signal-to-noise ratio as the signal passes through the receiver; a lower number means less added noise.
What is the purpose of a pre-selector (front-end bandpass filter) in a superheterodyne receiver?
Answer: To reject image frequencies and strong out-of-band signals before the mixer stage
The pre-selector attenuates image-frequency signals and strong interferers before they enter the mixer, preventing them from producing spurious IF outputs.
In an FM receiver, the limiter stage that precedes the discriminator is used to:
Answer: Remove amplitude variations from the IF signal so only frequency variations reach the detector
Because FM information is encoded in frequency variations, the limiter strips unwanted amplitude noise before the discriminator detects the frequency changes.