[OZAPRS] HF APRS -2
Glen English VK1XX
glenlist at pacificmedia.com.au
Thu Dec 28 14:56:14 AEDT 2017
back into it today...
added facility to generate single ended signals on TX side for feeding
into the radio, and also generate WAVE files.
increase 1st version payload from 96 bits to 128 bits (fixed). that's
enough for a single packet to provide a bit of management and good
resolution location fixes. LDPC code is 640 cols x 512 rows soft
decoded 3 parity checks per column.
figuring out extension fields...and igate interface.
the idea is that if you want to send more than 128 bits in a
transmission, you send multiple packets, with a sequence number in them,
and reduced overhead on the consecutive packets by means of a hash on
the sender. Took that idea from V2 protocol (1984 Doug Lockhart VE7APU)
Why only 128? well as the coding matrix gets bigger, the degree of CPU
workload goes up at a square rate roughly.... and we want t be able to
run decodes on modest hardware.
Unlike AX25, there isnt a 0.5 second flag transmission on the front, the
sync overhead is approx 5% of the total transmission.
currently set to 46.875 sps, might double that ...
might have it released tomorrow.
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