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Continuous Tone Coded Sub-audible Squelch

With a mouthful like that, you now realize why is always abbreviated to CTCSS. Many manufactures of two-way radios use a trademarked name for CTCSS. Motorola calls theirs "Private Line", General Electric call theirs "Channel Guard", E.F. Johnson's trade name was "Call Guard" and RCA's was known as "Quiet Channel", just to name a few. They all however, are the same thing.


A Low Level, Precision Hum

In a nutshell, that's all that CTCSS really is! When you transmit on a two-way radio, a very low level hum is added to your voice. All of your other radios are looking for this particular hum frequency. When they finally see it, they turn on the speaker of the radio and your voice comes through.

Other people may use the same radio channel as you, but they have different CTCSS hum frequencies, so your radio doesn't turn on its speaker for them, only your own group.

You normally don't hear the hum since it is at such a low volume, plus most radios have a special circuit to keep it from reaching the speaker. At the very most you may hear it if someone has their radio keyed, but is not talking.


What is Needed for CTCSS?

Each two-way radio needs to be equipped to send and receive CTCSS codes. All new two-way radios have the ability already built-in. In older radios you may need to purchase and install a small circuit board to do the work. Costs of a board will generally range from $60.00 to $100.00 plus installation depending upon the features and what type of radio it needs to control.

Almost all radios, old and new, can have a CTCSS circuit board installed into them. When you install CTCSS in a radio system, it needs to be all or none. Either you install it into all of you radios at the same time, or you don't install it at all. If you try to equip only some of the radios, then either the units with it installed will have to leave it off to hear the non-equipped units, or if they do turn it on then the non-equipped units will be unable to contact them. There is no halfway point.


So CTCSS gives me a Private Channel?

No! It's often misunderstood that CTCSS will give the user a private channel, but it does not.

You are still on a radio channel with other users who have just as much right to be their and use their radios as you do. CTCSS simply makes your life quieter. With CTCSS you don't hear radio transmissions of other people as they use their radios, but your own group of radios comes through just fine when they need to talk to you.

When you transmit with CTCSS, you must monitor the channel just prior to talking to make sure that you are not disrupting someone else's conversation. If another person is talking, FCC rules and regulations require you to wait until they are done before you begin.

In most instances, when you pick a microphone out of its hanger the CTCSS is disabled and automatically goes into monitor mode for you to listen before transmitting.


Warning! Technical Boring Stuff Ahead

There are 32 "Standard" Electronic Industry Association (EIA) CTCSS tones that can be used. They are designated by some companies as letters, and others by the exact frequencies. If they have a letter, they are considered one of the EIA standards are universally accepted (except for the ZB listed below). We have listed both the designation and the frequencies below ...


Standard CTCSS Groups

Code Group A
Code Group B
Code Group C
Non-Std
XZ
67 Hz
XA
71.9
74.4 Hz
69.4
XB
77.0
YZ
82.5
79.7
97.4
YB
88.5
ZA
94.8
YA
85.4
159.8
1Z
100.0
1A
103.5
ZZ
91.5
165.5
1B
107.2
2X
110.9
171.3
2A
114.4
2B
118.8
179.3
3Z
123.0
3A
127.3
Special Non-EIA
183.5
3B
131.8
4Z
136.5
ZB
97.4
189.9
4A
141.3
4B
146.2
196.6
5Z
151.4
5A
156.7
199.5
5B
162.2
6Z
167.9
206.5
6A
173.8
6B
179.9
229.1
7Z
186.2
7A
192.8
254.1
M1
203.5
M2
210.7
M3
218.1
M4
225.7
233.6
241.8
250.3

As a general rule, stick to the EIA standard tones unless they are already in use by someone else. Non-standard Splits can cause problems with older decoders operating on either side of the split frequency.

One other item on CTCSS selection. I personally stay away from the 136.5 Hz when doing CTCSS assignments. The Motorola DPL (Digital Private Line) has a turn off "burst" that comes in at an audio frequency of about 136 Hz, so you may end up with your radio clicking for no apparent reason. Pick another CTCSS instead.

If your in a country which uses 50 Hz commercial ac power, you may want to avoid 100Hz as your CTCSS code since it would be a first harmonic of the 50 Hz, which could cause a channel to open when someone transmits from a base station using an AC to DC power supply.


How do I know which CTCSS tones are being used?

There are no records kept by the FCC that show CTCSS tones in use. It can be, quite literally, trial and error!

Most radio communications companies keep records of their own customers, and in many areas a quasi-structure between the companies has been arranged to divide up the available tones so they don't overlap, but there is no sure way of knowing until you try.

When you install CTCSS, you pick a frequency (maybe after talking to a local communications company to find out which ones they favor or suggest), and then put it on the air. If you are infringing upon an existing radio user that already has that tone, then you must change. The rule of the land is "the last one on must be the one to change any offending transmissions".

So you change to another tone, usually be changing a small switch and try again until you find an unused tone. It is a good idea to use one radio as your search radio, and to allow at least one week of time to pass before you consider the CTCSS tone good. Another user may be on vacation or out of the area for at least a week, so you have to give them time to advise you that you are using the same CTCSS as them.


A lot of trouble?

No... not really. If you do the up front work, and have a bit of patience, the payoff of a quieter channel is well worth the effort. You don't have to listen to all the other radio traffic, and when you hear a voice over one of your radios, you automatically know its one of your group!


CTCSS Decoders in other Equipment

Decoders can be installed in most all types of communications equipment

bulletScanners
bulletPagers
bulletAlert Monitors
bulletOne-way Control Systems
bulletSCADA

The decoders perform their function to filter out unwanted transmissions, and make for a more disciplined radio environment.

 

 
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