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[aprssig] was Re: Interference on 144.390 now OMNI DF

Brian Webster bwebster at wirelessmapping.com
Thu Mar 9 03:48:53 UTC 2006

	I had always thought your implementation of this Omni DF was cool and also
sad that the idea never caught on. I think too many hams assume the only way
you can DF a signal is with beam antennas and running around. With maps and
reverse Boolean logic plotted you get the ability to at least narrow down
the search real quickly. Do you think it might be possible to further refine
your system to not color in the rings but rather color in the area outside
the rings of? This might help illustrate your concept better and would show
area to look rather than where it is not. I think you would have to do a
little assumption of direction to eliminate the areas opposite of the
possible area being shaded in but that seems easy to figure out once you
have at least 2 stations reporting. Kind of like how the GPS receivers
ignore the obvious wrong position out in space.
	One thing that might be worth mentioning is that in the GIS world, maps
that show any theme or represent any data should never try to convey more
than 4 topics or points. The reasoning behind this is that the human eye and
mind get too confused and have to think and decipher what the map maker is
really trying to show, thus losing the effect of the map conveying obvious
meaning of the raw data at hand. Maybe your omni DF system fell fate to that
same basic concept. If you can just point out the areas where to look rather
than where not to people might get more excited about this feature. This
requires much less thought and gets your same point to the end user. Just my
2 cents as I remember having to read and re-read your documents on this and
finally figured it out after many days of thought and how it could possibly

Thank You,
Brian N2KGC

-----Original Message-----
From: Robert Bruninga [mailto:bruninga at usna.edu]
Sent: Wednesday, March 08, 2006 10:26 PM
To: tacos at amrad.org; aprssig at lists.tapr.org; n2csq at madxra.org;
vws at mail.viennawireless.org; farc at mailman.qth.net; mcfadyenusa at yahoo.com
Subject: [aprssig] Re: Interference on 144.390

>As of midnight Tuesday night... there is a repetitive
>continuous data signal on 144.390, causing severe
>disruption...Can anyone with 2m beams please DF it...
>I've got it S9 on a discone at 145 feet in McLean...
>It is... S9 on an omni antenna in Sterling, and ...
>heard at S4 near theintersection of Rt28 and Rt50.

Entering that data into APRSdos yields a solution probably
at Dulles Airport.  Took me 2 minutes tops.  To see the
APRSdos plot, see:

This stuff was fundamental to the design of APRS
since all APRS stations are supposed to have their
antenna-height-gain included in their fundamental
position reports (except for UIview).  From this, APRS
knows the range of your receiver and can plot overlaping
signal contours inversly proportional to signal.  The
point near the edges of intersecting brighter colors
is the location of the signal.

If we could just get people to listen and make signal
reports on any signal.  Even if you do not hear it,
THIS IS VALUABLE.  it instantly BLACKS OUT all the
area around you where the signal cannot be.  THis
very rapidly eliminates more area usually than "heard"
reports contribute.  There are no "negative" reports
shown here, but believe me, they are very valuable
since you usually get moer of them that actual
heard reports.  but the ALL contribute to the picture.

APRS has all this built in.  I am saddend that this
fundamental aspect of APRS was left out of most
follow-on APRS clones...

de Wb4APR, Bob

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