Dom Dahl vk2hj69 at gmail.com
Tue Sep 23 15:26:42 EST 2014

Hi Owen

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)

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.



Ambiguous positions

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.

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.

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.

On Tue, Sep 23, 2014 at 3:00 PM, owen <owen at owenduffy.net> wrote:

> Hello All,
> In the past, I have been a devotee of MIC encoding as it reduced packet
> size, reducing channel utilisation and increasing probability of
> successful transmission.
> But... I have review that position seeing the existence and continued
> operation of nodes that corrupt MICE packets.
> An example of the effect is VK3TKK-9's track up the Hume today, see
> http://owenduffy.net/files/Screenshot%20-%2023_09_2014%20,%2013_20_03.png
> .
> No, he is not drunk... his MICE packets are corrupted by VK2ZEN-5 and
> hence the gross track errors.
> My suggestion is to NOT use MIC encoding as there would seem little
> chance of fixing network infrastructure.
> 73
> Owen
> _______________________________________________
> OZAPRS mailing list
> OZAPRS at aprs.net.au
> http://lists.aprs.net.au/mailman/listinfo/ozaprs
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