[aprssig] APRS Omni-DFING (add a slider)

Robert Bruninga bruninga at usna.edu
Fri Jan 16 09:38:50 CST 2015


A local group is trying to DF an interfering weak carrier to their
repeater.  I said it should be trivial if they can just train their
membership to tune in the repeater INPUT whenever they hear the interfering
signal come up and then simply plot those signal strengths and locations on
the map using the APRS Omni-DFing technique. (you don’t really need APRS.
Just some crayons and amap)…

That is, every station’s S1 signal strength contour circle is proportional
to his PHG (HAAT).  And the size of the S1-S9 circles are INVERSLY
proportional to signal strength.  That is a very weak S1 circle is plotted
as dark grey at the full HAAT range.  But a very strong S9 circle is
plotted as RED but only to one-TENTH the size.

See http://aprs.org/dfing.html

This works very well since it lets 100% of hams in the area participate and
give good data instead of only 1% who could actually report a beam
heading.  Then the human brain can look at all the overlapping and
intersecting data, and get a good idea of the probability where the signal
cannot-be and where it more likely is.  And then refine the search.

But there is ONE OTHER VARIABLE.  That is the PHG (Power and HAAT) of the
interfering signal.  In that case **ALL** the omni-signal-circles on the
map ALL have to scale INVERSLY to the unknown signal’s power and HAAT
(which is unknown).

Hence THIS EMAIL.  I ask all authors that plot APRS Omni-DF-Circle reports,
to consider adding  a TX-RANGE-SLIDER knob.  This knob then simultaneously
scales ALL circles on the map at the same time.  The human trying to make
sense out of all the signal plots then slides the unknown’s TX-RANGE-SLIDER
up and down until the circles make sense.  Here are two extreme examples.

WEAK SIGNAL: All the circles are reporting very weak signals or not-heard
circles so they are LARGE circles and all the circles all overlap the
entire area.  Well, if the signal is a few milliwatts being leaked from a
cable TV cable only a mile from the repeater, then the large overlapping
circles do not indicate an area of concentration.  They all overlap there.
But if the TX SLIDER is brought low, then ALL the circles get smaller and
there is a point where the circles no longer completely overlap but tend to
intersect only in a few areas where the signal is most likely found.

STRONG SIGNAL:  All the signal circles are strong and all  overlap and make
no clear intersection.  Then move the slider towards a stronger assumed
transmitter and ALL the circles will inversely-proportionally reduce in
size.  Again, a place will be found on the slider  where the circles do not
overlap as much and the area of intersection is more obvious.

STRONG SIGNAL FAR AWAY:    None of the circles intersect.  They are just
islands of red, they all hear the signal strong.  SO one has to run the
slider UP until these circles begin to intersect to indicate the area of
interst.  Though, what is really needed is signal reports from farther
away, to at least get the gernal direction as bing completely off the map
of all the existing reports.

Anyway, having this variable slider on OMNI-DF plots would be a huge
benefit to finding the optimum solution which is the unknown TX signal’s
Power and HAAT.

Note:  That last example is what was my only failure with this technique.
Nothing made sense.  Turns out the signal was from a mountain top over 150
miles away, so no amount of local plotting (all of us in the same area)
would yield results since we were all getting the same signal dependend
ONLY on  our own HAAT and nothing else.

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