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README.DF
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1993-05-04
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USING APRS FOR DIRECTION FINDING
APRS is an ideal tool for rapidly triangulating fixes to locate a hidden
transmitter, an interfering signal, or for tracking balloon payloads. APRS
instantly plots vectors from all stations making a signal report and the
intersection of these lines of bearing indicates the location of the target
signal. To see a sample, load the file named FOXDF.BK into APRS and see the
results of our DF on a constant carrier on our local 145.05 packet frequency.
The bearings from W3ADO and W3DTN were actual measured beam headings. The
third bearing from N3BFO was added to the file to show how great it would be
if we had three stations reporting instead of just two.
To accomplish this triangulation, each participating station simply
enters his bearing to the target into his own station's course by hooking
himself and using the INSert key to update his stations report. By setting
the speed field to zero, this alerts all APRS stations that the course field
is being used as an antenna bearing indicator. As soon as
two or more stations are reporting a line of bearing to the target, everyone
can predict the intersection of the lines by pressing the X key for a cross
fiX. As a further aid, the R key can be used to superimpose a set of range
rings on the screen for estimating distances for subjective analysis of
signal strnegths.
Even for stations not running APRS, their lines of bearings can be
quickly entered by any one APRS station using the alt-A key which adds them
to everyone's map in real time. A direct entry feature has also been added
for placing a reporting station on the map by entering his numeric LAT/LONG.
This makes plotting of distant stations on the map easier without a lot of
cursor movement. This feature is useful when taking reports by voice over HF
for example during a balloon tracking event. Non APRS packet stations can
also automatically report their lines of bearing into the system by simply
entering a beacon text in the APRS format with their line of bearing. See
the README.DUM file.
Finally if a mobile fox-hunter is equiped with GPS or LORAN-C, his
movements will also be tracked so that he can be vectored into the target's
location.
As a further note, the line of bearing feature can be used routinely by
any stations using a beam to indicate their beam heading to all other APRS
stations.
Eventually I want to add a signal strength contour display so that single
stations can report simply their relative signal strength on the jammer, and
intersecting circles from each station can also be used in the triangulation
process. Feedback on this application of APRS is welcome.