Ah, yes, the (in)famous 567. It could be quite good at what it was designed
to do. The datasheets and application documentation were actually very
helpful. Being TTL compatible they stressed the power supply with current
spikes so a bunch of caps were needed on the supply buss near the chip.
Their main limitation was the TC of the external timing resistors and caps.
They would often take 14 or more cycles of the incoming tone to detect it,
especially if this tone was nearly 180 degrees out from the free running
frequency of the 567 PLL. (There was a kluge around this using two 567's
running in quadrature and OR-ing their outputs.)
As someone mentioned they are fairly level sensitive to the incoming tone.
And they had problems with sub-harmonics.
Their outputs could chatter giving multiple tone counts, not a good idea
driving TTL logic. This often occurred when the level of the incoming tone
was near the detection threshold or when a tone near the natural PLL
frequency was present. (Like the 103.5% difference in adjacent CTCSS tones
for example.)
I used the 567s successfully to decode various tones used in commercial
broadcast applications but these tones were fairly widely spaced. And many,
many hours of R&D were involved to tame them.
This was in the middle to later 1970's when the 567 was new technology. I
would not dream of using them for anything serious today. There are much
better options available. Ebay often has decoders for under $30, sometimes
less than $20.
73,
Al, K9SI
CTCSS Encoder/Decoder
Posted by: "James" ka2...@gmail.com ka2ajh
Date: Thu May 6, 2010 7:36 am ((PDT))
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.
