[aprssig] APRS POST HTTP

Nick VE3NNW tapr at noseynick.com
Sun Mar 8 12:35:00 EDT 2020

John Gorkos wrote:
> Please review this treatise on packet lengths inside APRS:
> http://lists.tapr.org/pipermail/aprssig_lists.tapr.org/2016-November/046312.html

Reviewed, however, some technicalities are explained in the linked
article. An APRS-IS line is:


The "APRS PACKET" part might be limited to 255, but the line sent to
APRS-IS includes some of the outer header fields (the path etc) so can
be longer. If I understand the doc correctly, it thinks 317B

PLUS, as you yourself pointed out, when submitting by UDP you need...

user CALL pass 00000<linefeed>[above line]<linefeed>

Adding presumably another... 24B? Possibly more for suffixed CALLs?

IN ANY CASE, we're not talking about using this ESP library to send ANY
APRS data, you're hand-crafting some WX format packets, your total UDP
packet would be:

26B?     user CALL pass 00000<linefeed>
????     [insert actual WX/data here]
2B       <CRLF>

If you're limited to 256B UDP by your ESP library, you have approx 207B
remaining for your telemetry/WX, however if I'm reading APRS101 right,
most WX packets are, at most:

1B       Pkt Type
7B       Time
8+1+9+1B Lat+Sym+Lon+Sym
7B       WindDir/Speed
4B       Gust
4B       Temp
4B       RainLastHr
4B       RainLast24Hrs
4B       RainSinceMidnight
3B       Humidity
5B       BarometricPressure
1B       AprsSoftware
2-4B     WxUnit
67B TOTAL ... and you still have 140B left for comments?

The longest (legal) telemetry looks like 5+7+7+6+6+5+6+5+4+4+4+3+3+3 =
68B, still leaving TONNES inside your 256B UDP packet

Look at MIC-E formats if you wanna pack even more into a smaller space.

Out of curiosity I also reviewed yesterday's APRS-IS captures, looking
for the longest lines, and...

> 255 is better than "the best" you can do
... except:

6390 lines were longer than 260B yesterday
3745 were longer than 280B
2366 were longer than 300B
1896 were longer than 320B
330 were bigger than 330B
55 were longer than 340B

Some of the FAIRLY long ones seem to be wx forecasts, but not in any of
the legitimate WX formats:

CHAUD/SATURE HUMIDITE/VAR.: Temp.:27.50°C/HR:98%/P.atm.:1012.65mbar //
JOUR: Tmin:26.60°C/Tmax:28.00°C/Tmoy:27.16°C/dT:1.40°C // MOIS:
Tmin:25.10°C/Tmax:31.80°C/Tmoy:27.81°C/dT:6.70°C /

All of the stupid-long ones are one weirdo self-declaring a "STATE OF


"Nosey" Nick Waterman, VA3NNW/G7RZQ, K2 #5209.
use Std::Disclaimer;    sig at noseynick.net
IBM: It's Bullshit Mommery

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