Continuous Tone-Coded Squelch System (CTCSS)
CTCSS is a sub-audible tone that can be added to a frequency to help reduce interference from other users of the frequency. In most cases it is used to eliminate interference getting into a repeater system. This can be the case where there are a number of repeaters at the same site and harmonic frequencies created by those system can cause interference.
CTCSS is also know by vendor names such as Private Line (or PL tone) (Motorola), Channel Guard (Bendix King & and GE), Quiet Talk (Kenwood) and Tone Guard (TG) or CallGuard (CG) (EF Johnson). Generally, in ‘radio speak’ the generic term “tone” is used.
CTCSS is used in several different ways. The primary mode is to get access, or open, the repeater. In this case your radio needs to transmit the tone with the input frequency.
Depending on the radio and manufacturer the ‘label’ in the radio can vary, i.e., in the Baofeng and variants the transmit tone (or tone into the repeater) is T-CTS in the menu. In other radios, and in most programming software, it is simply TONE.
RECEIVE TONE (tone squelch)
A receive tone, or tone squelch, is used to prevent your radio receiving interference. In this instance it is used as a squelch ‘control.’ Your radio must not only hear the output of the repeater but it must also hear the tone.
Not all repeaters are set to send a tone on their output. Therefore it is best not to program it unless you are having interference. If you do program the tone squelch and you are not hearing anyone on the repeater your first step is to disable tone squelch.
A receive tone can be used as an alert or pager of sorts. In normal mode no tone is transmitted by the repeater and a user has his radio set to use a transmit tone only. In an emergency the repeater is programmed to transmit a tone.
At night, or any time the user doesn’t want to hear normal chatter on the repeater, the user changes to a memory channel where they have tone squelch set. That user will only hear the repeater if the transmit (tone squelch) is turned on.
Any user with no tone squelch set will still hear the transmission regardless of whether the repeater is sending a tone or not.
Some repeaters use split tones, i.e., one tone is used as the transmit (input) tone and another for the tone squelch. This can be done where linked repeaters overlap, so you use a different transmit tone to get into one versus the other.
There is an industry standard list of tones. In most cases the actual number of the frequency is listed, i.e., 127.3, or a two-character code utilized by Motorola, such as 3Z (for 127.3). However, it should be noted that the manufacturers of the ‘bubble pack’ FRS/GMRS radios use a number or letter to designate the tone and they are not consistent. See the table below for tone designators in various FRS radios.
The use of CTCSS or DCS tones DOES NOT provide any security on a channel.
Digital Coded Squelch (DCS)
DCS is a digital version of CTCSS that puts a continuous stream of digital data on the transmitted signal. As with CTSCC the different vendors have their own names; Motorola calls it Digital Private Line (DPL), GE uses Digital Channel Guard (DCG), and Icom uses Digital Tone Squelch (DCS).
It functions in the same way that CTCSS does.
If you can hear people on the repeater but you can’t bring the repeater up/they can’t hear you then check that you have the right pl/dcs and that it is being sent. Some radios have a setting to select the tone and another to turn it on.
Another thing to check is that the shift and offset are correct.
If you can’t hear people but see the receive light on the radio on check to see if you have tone or dcs squelch set. Not all repeaters send out a tone so turn receive or tone squelch off.