T4B08

AMATEUR RADIO PRACTICES · Operating controls: frequency tuning, use of filters, squelch function, AGC, memory channels, noise blanker, microphone gain, receiver incremental tuning (RIT), bandwidth selection, scanning function; Digital transceiver configuration; DMR code plugs and talk groups

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What is the advantage of having a choice of receiver filter bandwidths in a multimode transceiver?

APermits monitoring several modes simultaneously by selecting a separate filter for each mode
BPermits noise or interference reduction by selecting a bandwidth matching the mode
CIncreases the number of frequencies that can be stored in memory
DIncreases the amount of offset between receive and transmit frequencies

Why A receiver filter passes only a slice of spectrum to the detector, so everything outside that slice, noise and adjacent signals alike, is rejected. Matching the filter to the mode's actual bandwidth lets the wanted signal through while throwing away the rest: roughly 500 Hz or less for CW, about 2.4 kHz for SSB, and 10 to 15 kHz for FM. Using a wider filter than the mode needs just lets in extra noise and interference with no gain in readability.

Watch out Monitoring several modes at once is not what multiple filters do; a receiver still demodulates one signal at a time, and the filters are alternatives, not parallel channels. Memory count and transmit offset are unrelated functions.

Filter bandwidth = mode bandwidth. CW narrow (~500 Hz), SSB medium (~2.4 kHz), FM wide. Wider than needed means more noise.

HamSandwich explanation, first draft. The question and answers are the NCVEC text.

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