[aprssig] Deviation meters

Stephen Brown Jr stephen.brown75 at gmail.com
Wed Apr 4 17:31:23 CDT 2007

Scott, if you engineer this one yourself, I think you should proudly
proclaim it the "Open Deviator"



On 4/4/07, Scott Miller <scott at opentrac.org> wrote:
> > Audio drive to the transmitter play an equally, and maybe more,
> > important role.
> And this is really what I'm hoping to come up with a tool to set - i.e.,
> set
> your tracker/TNC to calibrate mode (alternating tones) and set the audio
> drive level to get appropriate deviation.  Assuming the transmitter's not
> so
> out of whack that at 3.2 kHz deviation it's clipping the high tone
> already.
> > More important is having the transmitted amplitude of the two
> > tones in
> You're preaching to the choir.  =]  Of course, as long as we've got D700's
> and such out there, there's no getting around the fact that some stations
> will transmit with no pre-emphasis.  I made a point of adding a
> pre-emphasis
> circuit to my T2-135 board, since the DR-135T doesn't provide pre-emphasis
> on the TNC input (not the one from the internal header, anyway).  I may
> add
> a jumper on future versions to bypass it if needed, though.
> > In the absense of a service monitor or oscilloscope, and if a simple,
> > peak reading device is used, adjust the audio drive until the desired
> > level is achieved, then back it off just a tad.
> This is what I've encouraged users to do.  Still, it'd be nice to have a
> small board that'd give you at least a basic indication that you've got it
> set right, even if it wasn't very sensitive and required the radio to be
> tuned to a known frequency.  I've got an Agilent service monitor, myself,
> and it's wonderful for checking my relative tone levels and deviation, but
> even used and several years old it was more than $3,000.  I'd like to be
> able to point people to an affordable option that's somewhere between the
> extremes of 'service monitor' and 'set it by ear'.
> Scott
> N1VG
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