Many many years ago when I was finishing college
electronics, my final year project was a repeater
controller. The danged thing worked really well,
I used 567s for the DTMF decoding, but they
really drifted around with temperature. Took
about an hour to stabilize, and then still needed to be "retuned".
I eventually replaced all that with an SSI chip
that did the decoding with a crystal as reference. It was rock solid.
The Hamtronics repeater REP-200 uses a 567
circuit for its PL decoder, but its real wide.
You can use 3 different tones at the same
time. Check their website. The schematic should
be on there for the PL decoder. May give you some ideas.
Get an off the shelf unit so as not to have any issues
73
Ian
VA2IR
At 11:03 AM 5/6/2010, you wrote:
On 5/6/2010 10:35 AM, James wrote:
> Hi Guys, We have been experimenting with building CTCSS Units using
> the 567 Tone Chip and good components, i.e. Caps, multi turn pots
> etc. The stability is not good in my opinion. We will set it to 107.2
> and the next time you check it is off enough to where it won't decode
> until it is re-tuned slightly. I am wondering what your experiences
> may have been with this CTCSS Chip. Many articles say they work well
> with the addition of a stable voltage regulator, so we added a five
> volt regulator, no difference in stability. Any comments and
> experiences with this and other chips would be appreciated. The
> availability of CTCSS Chips seems limited.
I've never seen anyone have real succes with those chips in that
application. Frankly, I think the internal components in the IC do not
have the tolerance and stability to handle it, so no amount of
high-tolerance components on the outside will make it usable.
They were never designed for that purpose anyway. They were for broad
decode app's in the audible range...cheap. Like a 1050Hz decoder in a
weather radio.
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