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[aprssig] NE567 tone detector (help)

Robert Bruninga bruninga at usna.edu
Wed Dec 14 01:34:31 UTC 2005


>>> John Magliacane <kd2bd at yahoo.com> 12/13/05 5:23 PM >>>
>For the LM567, it is.  I think the CMOS version runs
>the VCO at twice the detection frequency.

That's it!  I am using the CMOS chip but 
was using the bipolar docs...   Yep, downloaded
the CMOS spec sheet and sure enough, it runs
at twice the clock rate and its formula for the 
clock is even 30% different too:

F of PLL is 1/1.4 x R x C    (not 1.1/R x C as published)

F of operation is therefore 1 divided by 2.8 x R x C
and it is just what I am getting.

But now I am curious why my old book sas 1.1/R x C
and several responodents said theirs say 1/1.1 x R x C
I wonder if my old book is wrong there...  Oh well...

Thanks John and everyone else that jumped in there!
Bob, WB4APR



>>> bruninga at usna.edu 12/13/05 3:48 PM >>>
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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