Mark replied:

Stan,
Found the following article:

CTCSS stands for "Continuous Tone Coded Squelch System" This means the radio's squelch.. what keeps the radio quiet between calls... is operated by a special subaudible tone, rather than the existance of a signal... or radio "carrier" This is ALL CTCSS does.

Many FRS radios have this function. CTCSS tones are usually set up by entering a one or two digit "code" number in the radio. This corresponds to a specific tone frequency the radio emits when operating in CTCSS mode. CTCSS mode may be called; CTCSS, Quiet, Private, among other names.
See
http://members.tripod.com/~jwilkers/myth.htm

Granny replied:

That is correct,basically it prevents other users interupting your personal conversation,they can hear you and speak to you however because they don't have the correct tone you won't hear them.They usually feel very left out or think there is something wrong with their set.PS I think CTCSS is illegal unless prior permission is sought with The Department of Communications.

Tim replied:

Electrophone UHF's have what they call Selcall (selective calling)which sounds very much like CTCSS. How it works is by pushing the squelch button, you effectively turn off the volume or mute your radio. If someone knows your four digit code, they "ring" your radio by sending this code which removes the muting. The radio also starts beeping and the callers code is left on the radio. This is extremely useful if the radio is unattended at the time of the call, because it alerts you to the fact that someone has tried to call you, and has left an ID to return the call. When the muting is removed, your radio is effectively back on the open air waves, ie anyone can listen and respond to your coversation, so even though you are responding to selected call, it is not private. Select call is especially useful when channels are congested, and you want peace and quiet, or only want to take calls from people whom you have given your code to. They also have a paging system wherby if one of your receivers (especially a base staion) picks up a signal your mobile cannot receive, it will relay via the four digit code that someone is trying to call you. This is all a bit high tech for me and don't bother with it, but Select Call is excellent and the next best thing to having your own crystal in a HF or VHF radio.

Hope this helps,

Cheers, Tim.

Nigel replied:

CTCSS should only be used if your radio is also equiped with busy lockout, otherwise because you can't hear other conversations on the channel, you can quiet easily talk over other people which will be very annoying. CTCSS is now legal on CB but is not very well liked because of the above reason. On shared private channels (not CB) it works very well coz commercial sets use busy lockout as standard, but most cheap CB's with CTCSS don't have a busy lockout option. One of the cheapish uniden handhelds has busy lockout and the GME TX4400 has busy lockout. Selcall is a much better option coz it's more like making a phone call. A short set of tones is sent which makes the other users set beep (and unmute if it was muted) but then the conversation is just like normal CB in that you can hear anyone else on the channel.

Nigel replied:

One other thing. Some people mistaken believe that if they use CTCSS that people not using it can't hear them. This is not the case. CTCSS stops people using it from hearing those not using it, but those not using it hear the conversations of people using CTCSS.