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[aprssig] Point-to-point telemetry addressing

Steve Dimse steve at dimse.com
Sat Nov 25 00:15:01 UTC 2006


What jumps out at me is the packet is really long. Do you really need  
to add "Telemetry from East Homer, NY on 11/23/2006 at 11:11 PM" to  
every packet? This doubles the packet length and greatly increases  
the chance for collision. Though time delays do occur, they are quite  
rare, and the time a packet is received at findU should be adequate  
for your needs. findU is synced to a level 1 time server, whereas  
since your cottage does not have internet, the computer is probably  
not synced at all (there appears to be a consistant 80 second offset  
now) so findU's time is probably much more accurate even including  
propagation delays.

Looking at the packets, you seem to get about 70-80% through, with a  
shorter packet you will have even greater return.

You should also occasionally send a position packet so you will  
appear on maps!

Steve K4HG

On Nov 24, 2006, at 6:58 PM, VE7GDH wrote:

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