The classic NE-567 chip makes a fine CTCSS decoder with one major 
consideration. In a real world circuit the detection band-width is 
kind of wide, meaning you can and might also experience valid decode 
logic on the two tones each side of Frequency-Center. 

If you construct a well thought out circuit using all the expected 
considerations for frequency stability and control (voltage 
regulation and the right type support parts) the 567 will do 
what you want. 

There are/were a few commercial 567 CTCSS decoders on the market 
although it's not normally considered as the first choice. Because 
some people don't seem to want to read and apply the data sheet 
information the 567 often gets a bad rap in the decoding sub 
audible tone department. 

You'd think CTCSS Detection would almost be a "no brainer" when 
you want to build something simple and easy... but all the classic 
land mines will find those who don't read the mfgrs data sheets. 

I would toss out the idea of using/copying the Yaesu and/or 
Hamtronics 567 circuits...  The Yaesu circuit I have in my 
archives does both encode and decode using the same chip. 

cheers, 
s. 


> "James" <ka2...@...> 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.
>


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