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[aprssig] KPC3 and Deviation

Robert Bruninga bruninga at usna.edu
Tue Jun 6 15:48:29 UTC 2006

I never use the MARK-SPACE setting in any TNC, because
I do not trust the speech circuits to be consistent between
tones.  If there is any AGC action, then setting a single tone
at a time is pointeless (though most FM rigs dont have
any gain control)..

So the only fool proof method I use is to look on a scope 
and just be sure the packet and very quickly it is easy to
see if there is the right balance in tones.  *however*
this is a function of what "receiver" you are using with
the O scope.  So it also has to be taken with suspicion.
I have no easy answer.  Other than by ear.  There are
surely lots and lots of lousy sounding packets on the air.
But I know a clean one when I hear it...


>>> yahoo at davidarush.com 06/06/06 11:28 AM >>>
I'm using an old KPC3 that's been upgraded to 8.2, wired to a Yaesu 
1500M via the 6-pin mini-din on the back.

But I had trouble setting deviation "by ear", which I've usually done 
with all my APRS and packet gear, in between having access to better 
test equipment.

I just bought the MFJ-224 "2 Meter FM Signal Analyzer" so I could 
finally measure deviation myself, and discovered what was going on.

With the deviation jumper off, the deviation range I can get is about 
0-1.9 kHz on a mark tone and 0-0.5 kHz on a space tone.
With the deviation jumper on, the deviation range I can get is about 
3.7-4.0 on mark, 2.8-4.0 on space.

So with the jumper on and the pot turned as low as it will go, I seem to 
be doing okay, although I'd prefer it if I could tweak the deviation 
down a smidgen (or at least have the option of experimenting with it a 
bit lower).  With a "live" packet of real data, the meter shows about 
3.6 kHz deviation.

Has anyone else run into the issue of not being able to "hit" the 
deviation they want?

What is the optimum deviation for mark and space tones?

Using my trusty HT via conventional mic and speaker connections, I get a 
nice continuous 0-4.1 range on both mark and space tones, with the 
deviation jumper off.

David, ky7dr

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