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Continuous Tone Coded Squelch System CTCSS
CTCSS is a common way of coding two-way
radio gear to allow selective calling of radios in the same organization.
ie: Units with the same CTCSS code will be able to communicate together.
CTCSS is also known as PL in Motorola gear, Channel Guard in General
Electric gear, and Call Guar" in E.F. Johnson gear.
How it works:
The transmitting unit generates a tone that is broadcasted along
with the voice signal of the radio. The receiving unit recieves the
tone and opens the radios squelch circuitry if the tones match each other.
Most radios put a high pass filter in the audio output statge to filter
the CTCSS tone out of the audio. In urban areas and on commercial bands
there is usually more than one organization on an assigned frequency.
The CTCSS encoding method keeps the two organizations from hearing each
other's transmissions. Since there is still only one radio frequency
that these two groups are sharing, if both groups key their radios
at the same time and are geographically close to each other, they will
cause interference and usually nobody hears anything.
Motorola assigns a 2 letter code for ease of remembering the different
codes. Here is a list of the CTCSS tones in Hz and the Motorola PL
code.
67.0 XZ 69.3 WZ 71.9 XA
74.4 WA 77.0 XB 79.7 WB
82.5 YZ 85.4 YA 88.5 YB
91.5 ZZ 94.8 ZA 97.4 ZB
100.0 1Z 103.5 1Z 107.2 1B
110.9 2Z 114.8 2A 118.8 2B
123.0 3Z 127.3 3A 131.8 3B
136.5 4Z 141.3 4A 146.2 4B
151.4 5Z 156.7 5A 162.2 5B
167.9 6Z 173.8 6A 179.9 6B
186.2 7Z 192.8 7A 203.5 M1
206.5 8Z 210.7 M2 218.1 M3
225.7 M4 229.1 9Z 233.6 M5
241.8 M6 250.3 M7 254.1 OZ
Motorola also has a Digital PL system that uses a digital code instead of
an audible tone. Last I heard, Motorola will guarentee that their Digital PL
will keep other groups out of your radio system but they won't guarentee the
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