Uniden BC 278CLT Reference Manual page 13

4. To set the SQUELCH control to AUTO turn fully counterclockwise until control clicks into
place. Or, manually set squelch as follows:
Think of squelch as a gate. Turn SQUELCH fully counter clockwise. This raises the
"Squelch Gate" so high that only very strong signals can get through.
Turn SQUELCH fully clockwise until you hear a hiss. This lowers the "Squelch Gate"
so that everything gets through — noise, weak signals, and strong signals.
Turn SQUELCH back counter clockwise until the hiss stops. Now the "Squelch Gate"
allows only strong signals through.
10