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What is CTCSS?
Article by Alan Hill, N5BGC |
What is this tone that we need in order to use the Tesuque
Peak repeater?
With the quantity of radios in place on Tesuque Peak, there
is a very great potential for interference to our repeater
receiver. Commercial radio equipment has been using this scheme
for years to either cut down on interference or allow several
to use the same repeater and have an almost private repeater.
The tone is injected to the modulator after the filtering
of the microphone circuits. These filter circuits shape the
audio response from 300 to 3000 Hertz to be fed into the modulator.
In the receiver, this tone is filtered out and not heard.
It is used in the repeater control circuits to allow the transmitter
to be keyed only when that tone is present. There are about
35 tones spaced from 60 to 208 Hertz. They are generated either
by an analog circuit or sharply filtered digital signal.
The tones are not typically passed through from the receiver
to the transmitter in a repeater. It is normal to regenerate
them so the audio can be shaped before it is injected in the
transmitter. There is no tone on the repeater transmitter.
We had problems with the transmitter interfering with the
receiver if a tone was transmitted. When we removed it, the
troubles stopped.
Alan N5BGC
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