[aprssig] Duplicates evident on aprs.fi

[Heikki Hannikainen]

On Sun, 26 Jun 2011, Rob wrote:

> We are seeing a lot of duplicate packets for our area on aprs.fi to the point
> where it is warning "This station is transmitting packets at a high rate, which
> can cause congestion in the APRS network." I believe that duplicate packets are
> dealt with in the APRS-IS network (?) so the problem probably doesn't lie with an
> igate. Is this the correct place to report the problem and if not, where should I
> go. Here are the last few reports of my mobile tracker from aprs.fi raw:. Just
> about every packet has a duplicate and I've highlighted an obvious pair.

Unfortunately the highlighting is not visible on many email programs 
(white on black text display only).

I looked up the packets on aprs.fi. The packets have been modified by a 
digipeater or an igate, either by adding or by removing a space character 
in the end of the packet. Since the packet contents differ, they're not 
treated as duplicates by the APRS-IS, and they're not filtered.

If you switch the raw display mode from "Normal" to "Hex", the extra space 
character in the end of the second packet is visible. Right after "17C" 
(31 37 43 in hexadecimal) there is a space (0x20). You can find the space 
in the "Normal" mode too, by marking the text with the mouse - the space 
character is painted on the lines which have it.

The next step is to figure out which igate or digipeater is the faulty 
one. If the igate is stripping the space character (instead of adding 
one), it also helps to remove the (useless) space character from the 
OpenTracker's configuration.

> 2011-06-25 09:06:38 UTC:
> VK6UFO-9>APOT21,WIDE1-1,WIDE2-1,qAR,VK6EX-1:!\^\BEkisoOwVG/A=000054 14.0V  17C
> 2011-06-25 09:06:39 UTC:
> VK6UFO-9>APOT21,VK6RTH-3,WIDE1*,WIDE2-1,qAR,VK6HGR:!\^\BEkisoOwVG/A=000054 14.0V 
> 17C

   - Hessu