Gary Stern vk2zbb at gmail.com
Thu Sep 25 09:48:52 EST 2014

VK2TGB-7 tends to jump around when stationary.

Actually look at http://aprs.fi/info/?call=VK2TGB-7

over 14000 km ???

Its getting worse as time progresses ?


On 25-Sep-14 07:28, Owen Duffy wrote:
> Hi All,
> Corruption is commonplace in APRS.
> This morning, looking at VK2TGB-7 which has been stationary for the
> entire 48 hour history in aprs.fi and has beaconed every 2 minutes (yes,
> that is 2880 beacons for a station which did not move, repeated by
> several digis into the Sydney region and until recently, gated from
> APRS-IS back to RF by VK2ASY in Orange so that it travelled back via
> Orange, Ginini and Illawarra/Southern Highlands digs to the Sydney
> region again). Until Monday, I would hear each those posits 4 or 5
> times, so on average a VK2TGB-7 packet very 25-30s... if VK2ASY ceases
> his gating of this stuff to RF, it is an average rate of one posit every
> 60s (via Vk2RHR-1 and VK2AMW-1)... and yes, for a stationary tracker.
> But, one posit in those 2880 is interesting:
> 2014-09-24 03:09:34 UTC: *VK2TGB-7
> <http://aprs.fi/?c=raw&limit=&call=VK2TGB-7>*>S3T2W3,WIDE1-1,WIDE2-1,qAR,VK2NR-5
> <http://aprs.fi/?c=raw&limit=&call=VK2NR-5>:'N?9l <0x1c>>/ *[Duplicate
> position packet]*
> 2014-09-24 03:11:34 UTC: *VK2TGB-7
> <http://aprs.fi/?c=raw&limit=&call=VK2TGB-7>*>S3T0W3,WIDE1-1,WIDE2-1,qAR,VK2MB-1
> <http://aprs.fi/?c=raw&limit=&call=VK2MB-1>:'N?9l <0x1c>>/
> 2014-09-24 03:13:34 UTC: *VK2TGB-7
> <http://aprs.fi/?c=raw&limit=&call=VK2TGB-7>*>S3T2W3,WIDE1-1,WIDE2-1,qAR,VK2MB-1
> <http://aprs.fi/?c=raw&limit=&call=VK2MB-1>:'N?9l <0x1c>>/ *[Duplicate
> position packet]*
> The middle one is a most unlikey position change... exactly one
> character in the MICE encoded position changed. If this occurred in the
> AX.25 link, it should have been detected by bad CRC and discarded... so
> it has happened in the tracker, or in the iGate / APRS-IS infrastructure
> (and it is a single bit error in that case).
> I have noticed certain stations (including VK2MB) commonly figure in
> corruptions whereas others don't so it points to those stations as
> probable corrupters.
> Perhaps APRSdroid is the future, it bypasses all the problems inherent
> in radio links and flawed digis and iGates!
> Owen
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