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[aprssig] NE567 tone detector (help)

Robert Bruninga bruninga at usna.edu
Tue Dec 13 20:48:41 UTC 2005

The RAFT APRS  satellite will use a NE567 tone decoder chip
to detect the presence of a PSK-31 Control user.

I need help from someone that has used a 567 
before.  They have always worked for me before,
but I'm stumped now and on deadline.

 The book says the freq of operation is defined to be
1.1 divided by the product of R x C.
I'm using 12 k and .047 uF which should give
about  2000 Hz.  Problem is the PLL runs at 
about 1200 Hz and the only input that
triggers it is 600 Hz not 2000 Hz and there are 
no other false indications.  

It simply works solidly at 600 Hz just as advertized, 
but there are two facts that are inconsistent with
the book:

1) The working freq is off by about 3 (actually almost
equal to PI, but it would have to be 2*PI to be
a confusion between radians and frequency)...

2)  There is no mention in the book that the trigger
tone is ½ the PLL frequency.

I measured the capacitor and it is right on .047 uF.
The onlly other design components are the non-critical
bandwidth capacitor (1uF) and the output filter (1 uF).

Any ideas?
Im supposed to have this satellite finished by Friday!

Bob, Wb4APR

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