The delta tune is the CB name for a very similar function on amateur radios called RIT, or receive incremental tuner. The Delta Tune controls the frequency your radio's receiver is operating on. You may notice similarities to a clarifier control on other CB's, and while both these controls do similar things, they are not used for the same purpose. You may notice it doesn't matter where your delta tune control is set, however leaving it in the center detent position is recommended. That's because what the delta tune is changing is not really having any effect on modern synthesized PLL CB radios, as this control was designed more for older crystal based CB's.
It finely adjusts the receive frequency, but why?
On older CB radios, when the frequency the radio was operating on was mostly determined by crystals, there was a greater chance for other people to be slightly off frequency when they transmitted, the delta tune allowed you to tune those people back in so they were clear and on frequency again. Modern CB radios are more tolerant, and often more frequency stable, so the need to fine tune your receiver frequency is at this point more or less moot.
If it's not needed anymore, why do radios still have it?
Some people may still need it to talk to older crystal controlled radios. If you're not talking to an older, crystal radio (usually pre-1980) then the Delta Tune won't have much impact. As stated before, keep it in the 12:00 detent position.
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