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[aprssig] Ultimate APRS digi

Fredric Moses fred at moses.bz
Fri Nov 19 05:41:20 UTC 2010

Hi Bob, since the hardware isn't there we have built out something like it with software here at the detroit aprs digi site.  We have over the past few months started moving our digi/igates around the state from kantronics based digi's with aprsD to Aprx and kiss based tnc's..  Our southfield digi w8fsm-3 is running on the standard 144.390 1200 baud channel like normal. We added a UHF radio/tnc. it's 1200 baud at the moment but no reason it can't go to 9600.  We have it setup to take all UHF traffic to VHF.  The user doesn't have to change paths or anything if they want to use the UHF uplink they just change the channel on there radio. We have enabled it to also digi off the UHF port as sometimes us locals don't need to keep getting objects and other local data that we put out on the VHF channel back.  We have it setup to gate message traffic between the 2 only if that station is active on the UHF side..  It makes things flexible as lower powered mobile stations don't have to fight to get into the vhf side of the digi yet can still be apart of the network as they can run in vhf rx uhf tx.  or uhf rx/tx..

In an effort to get aprx based digi's which are hardened with no moving parts and low power usage. I have been testing the past few months a Linksys WRT54g running openwrt and Aprx. (w8fsm-6)  I added the 2 serial ports onto it and have it connected to a tracker2 tnc inside an alinco dr135 running kiss.  I am at a few months of uptime only downside is log storage it seems.. as there is only 16mb of HD space.  power usage is around 300mah at idle rx  and 7amps on tx.. It has been working very well so far and I have enough parts to build 4 more it looks like..

Another Idea I have to try takes a page from voice systems.  Using a central high power tx site and remote RX sites.  Aprx can use tcp network based streams for it's ports and if configured you can group different ports or receivers and it will de-dup packets and transmit the single clean packet that it hears first.  This would allow traveling users to take advantage of the system without changing a thing as you could have multiple stations getting into different receivers both sending there packets to the TX site where it would transmit both of them when the channel was clear..  I have hardened microwave links in place to try this just a matter of getting time to test/setup the config.
Fredric Moses - W8FSM
fred at moses.bz

On Nov 18, 2010, at 7:35 PM, Robert Bruninga wrote:

> New title for discussion.  
> I have added drawings at the top of APRS.ORG showing what I
> consider the ultimate APRS digipeater for greatly minimizing
> local congestion on 144.39 (or other country's freq):
> 1) Leave the 144.39 network just like it is now. (so it still
> works for visitors)
> 2) Provide an alternate INPUT channel (144.99?) TNC and receiver
> at every big digi.
> 3) The PTT/TXaudio of that alternate TNC is connected to the
> existing 144.39 XMTR.
> 4) 9600 baud UHF packets are also cross connected to 144.39 at
> 1200 baud
> 5) The eXternal Carrier Detect (XCD) lines are diode-ORed to
> both TNC's PTT lines.
> 6) 9600-to-9600 UHF packets can selectively remain on UHF only
> for future apps
> The result is vastly improved local user reliability since their
> input packets on 144.99 do not have to compete with any of the
> 144.39 congestion.  Yet 144.39 still has ALL info for ALL users.
> Until someone designs such a 3-input hardware, the closest I
> know of would be a KPC-9612 and another TNC combined at the
> site.  Its not the ultimate, but is the closest we can come for
> now?
> If there are better ideas, lemme know.  But my fundamental
> principle is that ALL normal local info resources should appear
> at 1200 baud on 144.39 national channel.  But by splitting all
> user inputs to alternate channels, the 144.39 can have 5 to 10
> times the capacity is has now.
> Bob, WB4APR
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