[aprssig] Realtime VHF Propogation using APRS-IS

A.J. Farmer (AJ3U) farmer.aj at gmail.com
Fri Aug 26 09:21:21 EDT 2005

On 8/26/05, Steve Dimse <steve at dimse.com> wrote:
>In particular, the rare propagation event, meteor scatter,
>Es, or whatever, is very likely to be missed.

The site may be presented as a propogation prediction site, but I
agree with you that PropNET is a much better tool for that job.  My
main interest was in the site's ability to show, even if not
absolutely 100% accurate, the stations heard direct by another
station.  To me, that is a very useful tool in determining the state
of the APRS network in a certain area.

> The net effect is that no payload data is filtered, one copy always
> gets through, but a LOT of path information is filtered. This
> filtering is essential, the APRS IS would need to carry perhaps 10
> times as much data were it not done.

I think I get it now.  The APRS-IS server that an IGate connects to
(or perhaps a tier 1 server up the chain) does the filtering based on
what it has already seen?  I didn't realize any filtering was done at
that level.  I understand that filtering happens as you described it,
I was just under the impression that it is done a little "further up
the chain".  I thought if you connected to what I would consider the
raw feed at a Tier 1 server, then you would see everything coming in,
totally unfiltered, which would allow this website to work as
described.  Where does the filtering occur?

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