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[aprssig] pointless text in the status (was: Preparing for a longroadtrip - VA)

Robert Bruninga bruninga at usna.edu
Thu Jun 1 13:11:11 UTC 2006


>>> n0yxv at gihams.org 05/31/06 9:02 PM >>>
>...How much more does each character add to the overall 
>loading of APRS. In other words if I use 10 characters in
>my status text instead of 20 have I cut my packet in half? 

No, simply look at the raw packet.  Count the bytes and then
do your ratio.   Usually a packet looks like this:

15 bytes   TX delay (300 ms and assume it takes half for your TX)
15 bytes   FROM/TOCALL required
15 bytes   WIDE1-1,WIDE2-1
*---------
45 bytes   total overhead

20 bytes   fixed station APRS position packet

Now add 20 or 10 bytes of status and you see that the savings 
of 10 bytes shortens your packet by 12%

HOWEVER, make that a MIC-E packet (D7 or D700)
where the position data is only 9 bytes and leave off the
20 bytes of STATUS text on every packet and you save
a much larger 27%.   That is why the D7 and D700 have
a STATUS text rate so that you dont have to send it on
every packet.  Just every Nth packet.

AND if you use the D7 or D700 for special events DIRECT 
simplex in PTT mode, then the savings is a whopping
45%  because 1) there is no TX delay, 2) No DIGI path

This use of PTT mode (.1 second burst on the end of
a voice transmission) is exteremely efficient and makes
operations at an event very practical.  In fact, it lets
all the D7 and D700 users use TWO simultaneous voice 
frequencies on their radios.

Use channel A (other than 144.39) for APRS and APRS
voice coordination with Voice Alert)

Use channel B for comms with the other stations at the 
event.

Back in 1994 I built the first Mic-E PTT device for  putting
APRS position data on the tail-end squelch burst so
that all mobiles could do APRS with just one radio.  THis
was to be the future of APRS on every frequency anytime
with one radio.
'
Then Kenwood came out with the DUAL band radio and
everyone just started using band A on APRS all the
time and so there was no incentive to use single band
radios with APRS PTT mode.   Yet it has such potential...

de WB4APR





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