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Hello Dom, All,<br>
<br>
An interesting possible explanation, and it may partly account for
the observations.<br>
<br>
However, here is one of TKK's posits:<br>
<br>
<span class="raw_line">2014-09-23 12:02:47 EST: <b><a
href="http://aprs.fi/?c=raw&limit=&call=VK3TKK-9">VK3TKK-9</a></b>>ST43ZL,<a
href="http://aprs.fi/?c=raw&limit=&call=VK2AMW-1">VK2AMW-1*</a>,WIDE2-1,qAR,<a
href="http://aprs.fi/?c=raw&limit=&call=VK2NR-5">VK2NR-5</a>:`MV<span
class="raw_bin"><0x1c></span>qzZ>/`";3}Just cruising ^:-}_"</span><br>
<span class="raw_line">2014-09-23 12:02:48 EST: <b><a
href="http://aprs.fi/?c=raw&limit=&call=VK3TKK-9">VK3TKK-9</a></b>>ST43ZL,<a
href="http://aprs.fi/?c=raw&limit=&call=VK2AMW-1">VK2AMW-1</a>,<a
href="http://aprs.fi/?c=raw&limit=&call=VK2RTZ-1">VK2RTZ-1</a>,WIDE2*,qAR,<a
href="http://aprs.fi/?c=raw&limit=&call=VK2ZEN-5">VK2ZEN-5</a>:`MV qzZ>/`";3}Just cruising ^:-}_" </span><br>
<span class="raw_line"><br>
Look at the </span><span class="raw_line"><span class="raw_bin"><0x1c>
in NR's submission, and see that in ZEN's for the same posit,
there is a blank.<br>
<br>
Some software developers think that AX.25 packets contain
printable characters, and substitute non-printables (eg with a
space as here) and so corrupt the packets. It seems aprsd
developers may have thought that way.<br>
<br>
MICE packets are not purely printable characters, and it is
presumptuous for any server handling traffic to edit the
contents of a another parties packet 'info' section.<br>
<br>
I think this problem in aprsd has been known for more than a
decade.<br>
<br>
Best way to avoid position reports if that is a concern is to
turn the thing off, and it saves bandwidth otherwise utilised by
garbage!<br>
<br>
73<br>
Owen<br>
<br>
<br>
</span></span>
<div class="moz-cite-prefix">On 23/09/2014 15:26, Dom Dahl wrote:<br>
</div>
<blockquote
cite="mid:CANkT2uPtOQmNXjYswzkyJgtw25=0dmrTS_F=6aUuEhOooLxn5w@mail.gmail.com"
type="cite">
<div dir="ltr">
<div>
<div>
<div>Hi Owen<br>
<br>
</div>
I thought the same thing to start with but his whole track
was from goulburn was all over the place. (I didn't look
back any futher)<br>
<br>
</div>
I was reading this the othe day and i think this would explain
what VK3TKK-9 setup is. Its more a security thing. Who knows
why you would use it but some people just really don't want
you to know there exact location.<br>
<br>
</div>
Cheers<br>
<br>
Dom<br>
<div><br>
<h2> <span class="" id="Ambiguous_positions">Ambiguous
positions</span></h2>
<p>Many APRS transmitters using MIC-E or uncompressed packets
can be configured to intentionally transmit less precise
positions. This may seem a bit backward at first, but there
are perfectly good reasons to do so. Some people might want
to transmit a rough location of their car without revealing
the exact parking spot where their expensive radio gear
spend their night in. Some might like some aspects of APRS
but wish to adjust the level of privacy by hiding their
precise location.
</p>
<p>Ambiguity is configured by setting the number of digits
which will be truncated from the end of the position.
Plaintext APRS positions are transmitted in degrees and
decimal minutes (DD° MM.mm'), with two decimals of minutes.
When ambiguity is set to 1, it'll be truncated to DD° MM.m',
2 will transmit DD° mm', 4 will transmit DD° only, resulting
in a resolution of 1 degree.
</p>
<p>The station in the following image has chosen to send
positions with 1 digit of precision reduced. It can be seen
that the car is driving the ring road, but the positions are
slightly off.
</p>
<br>
</div>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Tue, Sep 23, 2014 at 3:00 PM, owen <span
dir="ltr"><<a moz-do-not-send="true"
href="mailto:owen@owenduffy.net" target="_blank">owen@owenduffy.net</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">Hello All,<br>
<br>
In the past, I have been a devotee of MIC encoding as it
reduced packet<br>
size, reducing channel utilisation and increasing
probability of<br>
successful transmission.<br>
<br>
But... I have review that position seeing the existence and
continued<br>
operation of nodes that corrupt MICE packets.<br>
<br>
An example of the effect is VK3TKK-9's track up the Hume
today, see<br>
<a moz-do-not-send="true"
href="http://owenduffy.net/files/Screenshot%20-%2023_09_2014%20,%2013_20_03.png"
target="_blank">http://owenduffy.net/files/Screenshot%20-%2023_09_2014%20,%2013_20_03.png</a>
.<br>
<br>
No, he is not drunk... his MICE packets are corrupted by
VK2ZEN-5 and<br>
hence the gross track errors.<br>
<br>
My suggestion is to NOT use MIC encoding as there would seem
little<br>
chance of fixing network infrastructure.<br>
<br>
73<br>
<span class="HOEnZb"><font color="#888888">Owen<br>
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</div>
<br>
</div>
<br>
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