[aprssig] Point-to-point telemetry addressing

VE7GDH ve7gdh at rac.ca
Fri Nov 24 17:58:56 CST 2006

Michael W9IP wrote...

> I'm trying to maintain a telemetry link with our cottage (W9IP-2)
> about 35 km away....  There is a good APRS digipeater (K2AMB-3)
> near W9IP-1 and another good one (KB2FAF-10) near W9IP-2...
> W9IP-1's path to W9IP-2 would be
> APRS,K2AMB-3,KB2FAF-10,W9IP-2 and that W9IP-2's path to
> W9IP-1 would be APRS,KB2FAF-10,K2AMB-3,W9IP-1
> However, neither of these appear to work. The only addressing that
> seems to work is APRS,WIDE2-2, but that only works from time to
> time, when the two WIDEs happen to be K2AMB-3 and KB2FAF-10.
> I understand that I shouldn't expect 100% because of packet collisions,
> but so far specific addressing is just not working at all.  Any
> suggestions?

It doesn't really matter what the path from W9IP-1 to the cottage is. If the
cottage is W9IP-2, I would try a path of WIDE2-2. However, you said that you
were using APRS,WIDE2-2. That would only work if there was a digi that
responded to the alias of APRS. I'm assuming that you're not using UI-View
at W9IP-2. If you are, the "APRS" in the "unproto address" is really the
destination. Everything after that is the path. Try changing W9IP-2 so it
uses a path of WIDE2-2. This will work with any WIDEn-N digi that hears it.
If it so happens that you don't have a reliable path to a WIDEn-N digi, but
there are home fill-in digis within earshot that respond to WIDE1-1, you
could try WIDE1-1,WIDE2-1 instead. Would that make it to the IGate? If not,
you could increase the path to WIDE1-1,WIDE2-2. Generally speaking, fixed
stations shouldn't have WIDE1-1 in their path. My suggestion is for ONLY if
using WIDE1-1 will help you get to a WIDEn-N digi that would otherwise be a
bit iffy to get to directly. Re-reading you message, you said there was a
"good" digi near W9IP-2, so avoid using WIDE1-1 unless you really need to
use it.

The other possibility would be to use a specific path from W9IP-2 instead of
WIDE2-2. You could try KB2FAF-10,K2AMB-3 for the path from the cottage. Do
not include W9IP-1 as part of the path. First, it would be wasteful of
bandwidth by adding 7 bytes to every transmission, and it wouldn't be doing
any good because you are trying to receive the telemetry at W9IP-1, not
digipeat it.

The generic WIDE2-2 could spread out in multiple directions. By channelling
it to specific digipeaters, it would only propagate via the path that you
specify. However, if either of those digis went QRT, no other digis would be
used. I would probably go with the generic WIDE2-2.

You are right. You cannot expect to receive every beacon from W9IP-2. All it
takes is a packet collision for it to fail, or a burst of noise, intermod,
etc. If W9IP-2 has good "ears" it will at least hold off transmitting when
the frequency is already in use. There is always the "hidden transmitter"
that you can't do anything about, but if you have a decent antenna at W9IP-2
and the squelch is set loose or wide open, it will have a better chance of
knowing if the frequency is already in use. The danger of a loose squelch is
that if anything changes (i.e. something causes it to go open) it could end
up never transmitting. You are better off running with the squelch wide open
with the TNC set for software carrier detect.

Unless you are using UI-View at W9IP-2, get rid of the "APRS" in the unproto

73 es cul - Keith VE7GDH
"I may be lost, but I know exactly where I am!"

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