CTCSS / DCS Standard and Nonstandard Tones

The theory is, you can have many users on a single channel, and only those who have matching sub tones will hear the transmissions. Subtones are also used to privatize repeater systems, to "filter" out unwanted interference, or to simply assure a quiet radio when not in use. If you have ever purchased a "bubble wrap" FRS or GMRS hand held radio, they may be referred to as "talk groups", "private channels", or "sub channels". In fact, they are NOT private in the sense that you are carrying on a private conversation that no one else can hear. ANYONE who is monitoring the frequency can in fact hear and understand you regardless of what subtone you use, as long as their subtone setting is off or on the "0" setting. They are also NOT sub channels. You may have 38 "sub channels" on a primary channel, it is still the same channel or frequency as the primary channel setting.

Subtones have also been referred to by other companies as:

PL (Private Line)

Tone Squelch

Channel Guard (By GE)

Call Guard (By Johnson Radio)

Quiet Channel (By RCA)

They are all still the same thing with a few twists thrown in from time to time.

Bellow is a standard and nonstandard set of assorted "PL" technology