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[aprssig] Curious about bogus packets on Findu

Keith VE7GDH ve7gdh at rac.ca
Thu Sep 30 17:05:51 UTC 2010


Steve K9DCI wrote...

> Noticed some error lat long locations on Findu's Long term tracking.
> I've not seen this before. I save some of these images to show with my
> APRS talks.
> 
> www.findu.com/cgi-bin/track.cgi?call=k9dci-9&start=400&geo=usa.geo

> I also see some raw packets with the TOCALL (APK101) instead of the
> Mic-e data and don't know enough to understand that.
> 
> I couldn't see these glitches on aprs.fi.

from findu.com...

20100929191639,
K9DCI-9>APK101,WIDE1-1,WIDE2-1,qAR,N9XTN
:'|2y"4K>/]"7w}Delayed 45 minutes

from aprs.fi...
2010-09-29 19:16:39 UTC:
K9DCI-9>APK101,WIDE1-1,WIDE2-1,qAR,N9XTN
:'|2y"4K>/]"7w}Delayed 45 minutes [Invalid position ambiguity in mic-e packet]

They are the same packet. It would appear that findu.com used
the data and aprs.fi tagged it as having a problem.

Lynn suggested a digi or iGate using PASSALL turned on. I would consider
it a possibility if it was a random character that was altered, but a random
character change wouldn't change the MIC-E "to" field to APK101. Does
that make it a Kenwood? Is there any setting in it to tell it to only use valid
positions from the GPS receiver?

Also, there were some "high speed" beacons showing on aprs.fi. I would
suspect that the device was sending valid positions most of the time, but
sometimes used invalid positions from the GPS. Again, can the device be
told to use only valid positions from the GPS? The alternative is that the
GPS is outputting a valid position (or at least indicating in the $GPRMC
sentence when it isn't) but that the device is using it anyway... or that it
sometimes corrupts the data. Just guesswork here... e.g.

2010-09-29 18:49:12 UTC:
K9DCI-9>PP4Y2R,LARC,WIDE2*,qAR,NU0C-15
:'|R !Rv>/]"8:}Delayed 45 minutes [Location changes too fast (>500 km/h)]

PS - you are using MIC-E and a responsible two hop path. However, sending
"Delayed 45 minutes" with every beacon makes it 18 characters longer than it
needed to be. I know that it's nit picking, but shorter transmissions would yield
a higher chance of success for you and for others around you. Would it be possible
to send it as a message or bulletin, or does the Kenwood (D700?) allow you to
send a beacon comment every X transmissions?

Ummm... were you using a one minute beacon rate? That's probably OK when
you are operating in areas with very low APRS usage. If the frequency is busy,
backing it off to 2-3 minutes might be better. Of course, you could alter the
beacon rate based on where you were operating.

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





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