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[aprssig] Lotsa ears, big mouth concept.

Wes Johnston, AI4PX wes at ai4px.com
Mon Oct 12 16:10:19 UTC 2009


Just to throw something playful / constructive out there.  I had an idea a
few weeks ago about how to have a digipeater "network" that has many
recievers and one transmitter.  This is just a concept so bear with me.

1)have one high centrally located digi.  Output on 144.39 (or your local
aprs frequency).  This site has a 70cm transceiver for getting data from the
yet to be described receiver sites.
2)have several low receiver sites around town.  They listen on 144.39 and
send all data (KISS frames?) over the 70cm link to the main site.

So far, so good.  Here's the fun stuff.

First, how do we get the data from multiple RX sites to the main TX site?
We could just play with slot times and persist values, or better still, use
a DAMA connected scheme where all sites are polled.  Or we could do some
sort of token passing where each RX site knows all it's neighbors and knows
that it can transmit after hearing the RX site that has been assigned one
slot ahead of it - or after an appropriate delay if the other site doesn't
transmit.

Second, once a packet is transmitted from the main TX site, it will be heard
by all RX sites in the footprint.  How do we keep them from sending the same
packets back to the receive site in an infinite loop?  Make the TX site
transmit a PL tone (not 100hz).  Configure the satellite recievers to hear
everything (open squelch) and when the PL tone is decoded in the audio we
make a one-shot fire for just a few ms to glich the audio.  This gliched
audio prevents the TNCs at the receive sites from decoding the packets
because they will fail CRC... therefore there is nothing to send to the main
TX site.  The loop is broken, which in this case is a good thing.
As I said, just an idea... should make from good Monday fodder.
-- 
Wes
---
God help those who do not help themselves.
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