[aprssig] Advice requested please

Robert Bruninga bruninga at usna.edu
Sun May 5 09:28:41 EDT 2013

> When the distance between the Digi Tracker
>  and Android phone gets too high the Bluetooth
> link starts losing the first few characters ...
> usually with errors in the station callsign.

That can really  make a mess of things.

The good news is that the callsign has some inherent redundancy that you
might be able to incorporate on receipt to resolve these errors.  It sounds
like you have control over the code so you can maybe do hese things?

1) Force all callsign fields to exactly 9 bytes (six plus 2 digit SSID) at
the TNC

2) At the android, only accept the packet if it has exactly that format.
Then once confirmed it is OK, restore it to normal TNC2 format before
submitting to the APRSIS.

That shoul dbe sufficient if the only problem is dropped bytes.  If it also
includes garbles, then you can also check that all 6 bytes are uppercase
alphanumeric.  And that the SSID bytes are all correct.  You could even go
so far as to let the operator declare the typical callsign prefixes such as
in the USA, they are AKN and W.

Lastly you could add a CHECKSUM byte to the forced 9 byte call suggested
above and then remove that at the Android?

GOod luck.

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