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[aprssig] Help for course/speed/altitude etc HF APRS

Curt Mills archer at eskimo.com
Sun Apr 29 06:53:05 UTC 2007


On Sun, 29 Apr 2007, Jack Chomley wrote:

> I should have looked in the manual further :-) Looks like I can run the TM1+
> in NMEA mode and simply select a transmit timer value, so it does not continue
> to broadcast EVERY sentence the TM1+ gets from the GPS.

Yea but:  Check out the length of a GPRMC or GPGGA sentence compared
to the length of a normal APRS sentence.  Now check any of those
against Base-91 Compressed or Mic-E Compressed sentences.

FWIW:  The success rate of your packets getting decoded by other
stations depends greatly on the length of those packets.  The
shorter your packets are, the more will be received correctly.

NMEA sentences over the air are nearly the worst packets you can
send, length-wise.  I think the only ones that are worse are nice
long weather packets, or any packet with extensive comments at the
end.

If the TM1+ can do Base-91 Compressed or Mic-E packets, select that
instead.  If they can do Standard APRS packets instead of GPGGA or
GPRMC packets, you still win.

You might investigate getting an Opentracker 0T1x or Tracker2 to do
this instead, and use it in Base-91 mode.  OT1x kits are quite
inexpensive, and the latest OT1x version added receive capability.
I hope I got that model number right!

-- 
Curt, WE7U.				archer at eskimo dot com
http://www.eskimo.com/~archer
  Lotto:  A tax on people who are bad at math. - unknown
Windows:  Microsoft's tax on computer illiterates. - WE7U.
The world DOES revolve around me:  I picked the coordinate system!"




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