CTCSS Tones 

CTCSS (Continuous Tone Coded Squelch System) 

Michael, VK3FLMV

Some repeaters listen for CTCSS tones and will only ‘open’ the repeater if the correct CTCSS tone is sent; it uses Sub-audible tones – which are below the normal 300hz to 3Khz voice range of the radio and uses 67Hz to 254 Hz tone modulation which is sent on the carrier with the voice traffic. These tones are selected from an industry wide accepted list of tones and are usually available in your radio’s programming menu. 

The CTCSS system allows for Both encode and decode, encode implies that a sub audible tone is transmitted from your radio and decode implies that a sub audible tone is required to open the squelch on your radio receiver. 

In the amateur radio community CTCSS encode is referred to as Tone in radio programming and CTCSS decode is referred to as tone squelch. 

You could have a different encode and decode tone if your own transmitter is part of an interference problem 

As you may know our repeater VK3REC is off air for update and security maintenance. Part of this is the addition of CTCSS tone. 

In order to access REC, you will need a sub audio tone of 91.5hz most more recent radios will have tone built in but some of the older ones will not. 

Rec will also have Tone 91.5Hz on the output so if you wish you can use Tone squelch when using REC if you want to, provided of course your radio has tone decode as well as encode. 

Here is the information about these tone encoders. 

Refer to your radio’s manual to determine where to connect the tone. 

Usually Tone deviation is set at about 600hz but remember that the peak deviation including the sum of voice, CTCSS, and Touchtone signals in any combination. 

should be no greater than 4.5 Khz to 5Khz and should be symmetrically centered about the transmitter assigned center frequency. This means that if you install a tone board in a radio not designed to have one you may have to adjust the deviation after you add the tone. 

In the case of radio’s that have a tone board option this should be taken care of for you when you add a tone board provide that you connect the tone to the same connection that the optional tone board would be connected to. 

Now if you do not have a deviation meter you can try the following, 

Set a handheld to tone squelch 91.5hz and adjust your radio to a level that opens the squelch whilst transmitting tone only you adjust the level until you cannot hear the tone. This method is not perfect but should suffice in the absence of a meter. 

Thanks Michael. Regards Ed.

Sorry all the CTCSS boards that we had, have found new homes.

Attached is the schematics, the PCB layout differs. Link  CTCSS Encoder Schematic