Operating procedures
Use this page to explain what various functions of a transceiver are and how to use them.
Related wiki pages Apparatus
AF gain
Simply the volume control - like the one at your everyday BC radio.
Passband Tuning
Passband tuning manipulates the tuning circuitry of the transceiver, allowing "close together" signals to be separated - one is rejected by the filter, one is allowed to pass through. It is similar to IF shift, where the IF of the transceiver is shifted slightly to tune in slightly off frequency signals.
Passband tuning and IF shift are used because simply narrowing down the passband would produce muffling of any audio signals. Narrowing down the passband is however the best way to pick out narrow band signals (like CW and narrow band digimodes) from a noisy band.
External link from QST
RF gain
Controls the amount of pre-amplification in the RX before the first if stage is reached. It is very useful in QRN and other noisy conditions where otherwise SSB stations become unreadable. Take the RF gain back and have a QSO that would be impossible with full gain. Some rigs have also a switchable additional RF gain button, that sometimes has also an attenuation function. This in effect just widens the margin of the overall RF gain.
Roofing Filters
A roofing filter is used in an HF receiver and us usually found after the first receiver mixer. It's purpose is to reduce the passband of the first IF (first intermediate frequency) to between 6kHz and 20KHz. This in turn reduces distortion in any amplifier and mixer circuits.
Roofing filters are usually usually crystal types because of the steeper filtering curve that they produce.
Roofing filters can be much narrower than 20kHz when listening to very weak CW signals. In this case the filter may have a bandpass of as low as 250Hz. This also requires that the first IF in the receiver is below VHF, perhaps as low as 9MHz.
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