HAM Radio Extra Class Test Transmitter and Receiver Design Flashcards
6 cards from real HAM practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 HAM Radio Extra Class Test Transmitter and Receiver Design flashcards as text
What is a pre-selector in an HF receiver and what does it do?
Answer: A tunable bandpass filter ahead of the mixer that reduces image responses and intermodulation from strong out-of-band signals
A pre-selector is a tunable or switched bandpass filter placed before the mixer to reject signals outside the desired band, reducing image responses and preventing strong signals from causing intermodulation distortion.
What are 'birdies' in a receiver and what causes them?
Answer: Spurious internal signals caused by intermodulation of oscillator harmonics with other internal signals
Birdies are internally generated spurious signals that appear at fixed frequencies in a receiver, caused by mixing of harmonics of the local oscillator with other oscillators or clocks inside the receiver.
What does the third-order intercept point (IP3) measure in a receiver?
Answer: A figure of merit indicating resistance to intermodulation distortion from strong signals; higher IP3 means better dynamic range
IP3 is a theoretical extrapolated point where third-order intermodulation products would equal the desired signal; a higher IP3 indicates the receiver can handle stronger signals before generating significant IMD products.
What is the purpose of a noise blanker in an HF receiver?
Answer: To suppress impulse-type noise such as ignition interference by briefly blanking the receiver during detected noise pulses
A noise blanker detects short-duration impulse noise pulses and mutes the receiver for the brief duration of each pulse, greatly reducing the subjective effect of ignition and other impulse noise.
What is the 'image frequency' in a superheterodyne receiver?
Answer: A frequency on the opposite side of the local oscillator from the desired signal by the same IF interval, which can produce an unwanted response
The image frequency is separated from the local oscillator by the same IF frequency but on the opposite side; signals at this frequency mix to produce the same IF and thus appear as interference if not rejected.
What is the difference between receiver 'sensitivity' and 'selectivity'?
Answer: Sensitivity is the ability to detect weak signals; selectivity is the ability to reject adjacent-channel interference
Sensitivity describes the minimum signal level the receiver can usefully detect (often expressed as minimum discernible signal or noise figure), while selectivity describes how well it rejects signals on adjacent frequencies.