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

Andrew Rich vk4tec at tech-software.net
Thu Mar 9 21:03:47 UTC 2006


I cheat 

http://tech-software.net/aprs_rdf.htm

-----------------------------------------
Andrew Rich
Amateur radio callsign VK4TEC
email: vk4tec at tech-software.net <mailto:vk4tec at tech-software.net> 
web: http://www.tech-software.net
Brisbane AUSTRALIA 



-----Original Message-----
From: aprssig-bounces at lists.tapr.org
[mailto:aprssig-bounces at lists.tapr.org]On Behalf Of Robert Bruninga
Sent: Friday, 10 March 2006 12:53 AM
To: aprssig at lists.tapr.org; bwebster at wirelessmapping.com
Subject: RE: [aprssig] was Re: Interference on 144.390 now OMNI DF


>>> "Brian Webster" <bwebster at wirelessmapping.com> 03/08/06 
>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.

The problem is that outside the "PHG rings" is undefined unless
you somehow had 100% reporting from everwyhere.  In
otherwords, you cannot flood all areas that have "no information"
with a color that implies some conclusion about a subset of
that area...

When I get a "zero sig" report I can fill in his PHG circle with
solid black to show it "is probably not in here"... in fact,
this data is the most valuable because typically you get
far more "zero sig" reports than "sig" reports.

>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.

Boy do I agree with you there!  That is why I still use
the simple APRSdos for just about everything.  Its maps 
are simple, because it is the APRS and HAM radio that 
I want to see, not 3 megapixels of junk that hides the
data  I want to see!  Especially when some applications 
do not even show the fundamental APRS network data 
such as the extreme station variability of RANGE due
to their Power-Height and Gain.

Thanks for your feedback.
I DID learn something from this.  My plot was way off
because the signal was 50 miles away and on a 
mountain with its own signal circle covering HALF the
state!    thus, the intersection of the jammer circle of
impact with individual receivers PHG circles was TOTALLY 
vulnerable to the slightest variations in RECEIVER situation.  

Like a chaotic system., extremely vulnerable to slight
changes...

I now realize that my my OMNI DF system had assumed 
a FOX or mobile jammer who's "circle of impact" is smaller 
than most other surrounding "receivetrs".  In that case,
small variations in receiver circles and capabilties are 
less significant to the FOXe's smaller circle of influence.

I will be updaging my DOCS as soon as I get a chance
to point out how this system becomes chaotic  for long
distance high elevation weak signals, OR better, the
viewer must not jump to conclusions (like I did)  until he 
has enough data to rule out a far-off, high elevation jammer...

Just one more out of area report would have caused
a conflict in my solution, requiring me to then consider
a far-off signal.

Bob, Wb4APR

My OMNI-DI
-----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:
http://www.ew.usna.edu/~bruninga/aprs/DFinVA.GIF 

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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