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[aprssig] Proper deviation levels

Stephen H. Smith wa8lmf2 at aol.com
Tue Nov 28 03:44:57 UTC 2006


scott at opentrac.org wrote:
> I know this just came up recently, but I can't find it.  What's the accepted
> standard deviation for APRS?  Or more specifically, what should the
> deviation be for the high and low tones, so I can check pre-emphasis as
> well?
>
> And thanks to everyone who made suggestions for comm test sets.  I got my
> HP/Agilent 8920A today and I'm having loads of fun with it.  And when I'm
> not using it for testing, it makes a pretty decent (if rather expensive) FM
> radio for listening to music in the lab.  =]
>
> Scott
> N1VG
>
>
>
>
> _______________________________________________
> aprssig mailing list
> aprssig at lists.tapr.org
> https://lists.tapr.org/cgi-bin/mailman/listinfo/aprssig
>   

The peak deviation which will result from the higher of the two tones 
(2200Hz) should be about 3.5-3.75 KHz  .  This should result in the low 
tone (1200) deviating about 2.5-2.9 KHz.   [Deviation should be 
proportional to the modulating freq so the high tone should be 2200/1200 
of the deviation of the low tone.]      Theoretically the high tone 
could be deviated a full 5 KHz but there will then be no margin for 
transmitter or receiver frequency  error if the receiver has a narrow 
passband.   One is much better off slightly under-deviated in order to 
tolerate frequency error at either end.



--

Stephen H. Smith    wa8lmf (at) aol.com
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