CTCSS is the correct name, in the context of repeater usage. They're
considered sub-audible because they're outside the normal audio passband of
the radio. Internally, most radios roll off everything below ~300Hz and
above 2700 to 3000Hz.
Most CTCSS detectors require a fairly pure, clean tone. I'm not sure
what
the tolerance of the decoders are, but several of the CTCSS chips spec 0.3%
accuracy. That's 0.41Hz at 123Hz.
http://www.xs4all.nl/~hanvu/ctcss.html is a complete list of tones.
--jc
On Sunday 07 December 2003 16:48 pm, Chris Howard wrote:
> On Sun, Dec 07, 2003 at 10:00:07PM +0100, Chris Liechti wrote:
> > Chris Howard wrote:
> > > What I want to build is a little card that will
> > > output three different sub-audible tones, 100hz,
> > > 123hz, and another similar one. I would like three
> >
> > if "sub-audible" means that the human ear cant hear it then i have to
> > say that those frequenciey are clearly _not_ sub-audible. but it may be
> > that your kenwood transeiver has a band pass built in, so that it does
> > not transmit those low frequecies, or the receiver does filter them.
>
> I think the official name for them is CTCSS tones. Many repeater
> systems require them.
>
> > yes, timer a or b in PWM mode is well suited to generate tones.
> > that way you can program the frequency in CCR0 and set CCR1 = CCR0/2 for
> > a symmetric square output signal. you can also add a RC lowpass at the
> > output to filer out the harmonics.
>
> Thanks!
