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[aprssig] APRS iGate questions

Reuben Wells row at hopgarden.net
Sun Sep 5 17:01:39 UTC 2010


I have been building a standalone APRS iGate, using an Omnima embedded 
controller with OpenWrt (Linux) and running Aprx 2.0 
(http://wiki.ham.fi/Aprx.en). This has been up and running for about a 
week and everything looked to be working just fine (see M0RXW-B on aprs.fi).

However, yesterday afternoon I had a call from (M0NAS) that he was 
seeing very strange movements on aprs.fi. Now interestingly, when he 
called he was still seeing strange position reports coming through, but 
I had powered off the iGate almost 2 hours earlier at 14:27 UTC (15:27 
local).

Looking at the raw packets for M0NAS-9 on aprs.fi I see:

2010-09-04 16:01:10 UTC: *M0NAS-9 
<http://aprs.fi/?c=raw&limit=&call=M0NAS-9>*>UR0QW2,WIDE1-1*,WIDE3-2,qAR,M0RXW-B 
<http://aprs.fi/?c=raw&limit=&call=M0RXW-B>:`v?Dns1>/"4Y}Neil mobile
2010-09-04 16:20:16 UTC: *M0NAS-9 
<http://aprs.fi/?c=raw&limit=&call=M0NAS-9>*>UR0RV3,WIDE1-1*,G1DHB* 
<http://aprs.fi/?c=raw&limit=&call=G1DHB>,WIDE3*,qAR,M0RXW-B 
<http://aprs.fi/?c=raw&limit=&call=M0RXW-B>:`vA5n56>/"4`}Neil mobile
2010-09-04 16:40:21 UTC: *M0NAS-9 
<http://aprs.fi/?c=raw&limit=&call=M0NAS-9>*>UQ5YT4,WIDE1*,WIDE3*,qAR,M0RXW-B 
<http://aprs.fi/?c=raw&limit=&call=M0RXW-B>:`vI nSJ>/"45}Neil mobile
2010-09-04 16:43:51 UTC: *M0NAS-9 
<http://aprs.fi/?c=raw&limit=&call=M0NAS-9>*>UQ5YQ3,WIDE1*,WIDE3-1,qAR,M0RXW-B 
<http://aprs.fi/?c=raw&limit=&call=M0RXW-B>:`vG|n@,>/"4F}Neil mobile
2010-09-04 16:54:30 UTC: *M0NAS-9 
<http://aprs.fi/?c=raw&limit=&call=M0NAS-9>*>CQ,WIDE1-1*,WIDE3-2,qAR,M0RXW-B 
<http://aprs.fi/?c=raw&limit=&call=M0RXW-B>:>Neil mobile
2010-09-04 16:55:37 UTC: *M0NAS-9 
<http://aprs.fi/?c=raw&limit=&call=M0NAS-9>*>UQ5VU2,WIDE1-1*,WIDE3-1,qAR,M0RXW-B 
<http://aprs.fi/?c=raw&limit=&call=M0RXW-B>:`vD at mK3>/"4S}Neil mobile

And looking at the raw packets from my iGate M0RXW-B on aprs.fi I see:

2010-09-04 16:59:28 UTC: *M0RXW-B 
<http://aprs.fi/?c=raw&limit=&call=M0RXW-B>*>RXTLM-1,TCPIP*,qAC,T2ITALY:T#626,31.3,0.0,127.0,108.0,0.0,00000000
2010-09-04 17:00:22 UTC: *M0RXW-B 
<http://aprs.fi/?c=raw&limit=&call=M0RXW-B>*>APRX20,TCPIP*,qAC,T2ITALY:!5110.89NR00018.64E&Rx-only iGate (aprx2/OpenWrt 10.03 - row at hopgarden.net)
2010-09-04 17:01:26 UTC: *M0RXW-B 
<http://aprs.fi/?c=raw&limit=&call=M0RXW-B>*>RXTLM-1,TCPIP*,qAC,T2ITALY::M0RXW-B  :PARM.Avg 10m,Avg 10m,RxPkts,IGateDropRx,TxPkts

This doesn't make any sense to me as my iGate was physically powered off 
at 14:27 UTC whilst I was reflashing the device. Some how packets 
continued to be retransmitted for about 3 hours after the device was 
powered off. This would explain the strange tracks on APRS if the 
packets were being replayed out of order.

I've since been speaking with the operator of MB7UUE 
(g3rji.alanpaul at gmail.com - http://2e0avq.co.uk/) which is a new 
bidirectional gateway, that is bridging from the Internet to RF and he 
is also not sure what might be causing this.

Is it possible that MB7UUE could have somehow created a loop in the 
system? i.e. RF->Internet->RF->Internet.

Reuben
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