BMG Engineering, Inc. must warn anyone wishing to deal with malicious interference that the perpetrators may be dangerous! We cannot be responsible for your safety. To get you started on thinking about safety, please read the article on Personal Safety! Remember, YOU are responsible for your own safety!
Triangulation is usually done in situations where it is difficult or impossible to simply Home In on the signal. One example is when shore stations are attempting to "vector in" a rescue boat to a ship in distress. The distress signal may not be on the air long enough to locate the boat by Homing In. Even if it were, the rescue boats often do not themselves carry RDF equipment. A land example is the case where the signal is only short transmissions with long intervals between. These could be malicious harassment, accidental, or equipment problems.
Two or more DF teams stake out on hill tops, waiting for the signal to appear. When it does, each team takes a bearing and measures its compass heading. These headings are then corrected for the local magnetic declination. (The earth's magnetic pole is not actually located at the geographical pole. In the Los Angeles area, add 14.7 degrees. Contact a local airport to learn your correction factor.) These corrected headings are then plotted on a map. (See the page about using a compass.)
The best DF sites are high hill tops which are clear of obstructions, have an open view in all directions, and do not have transmitters on them. Such sites are difficult (if not impossible!) to find in Southern California. There are, however, quite a few lower sites which provide view into areas of interest. Even a bump in the ground (that gets you above the rooftops) can produce good bearings. Even though a site is a good one, effort should be made to refine the bearing taken, as there may be multipath present.
If the transmitter has gone off the air before it can be reached, the process is repeated using DFing Triangulation sites just outside the triangle of uncertainty (see Figure). Display figure as separate page. Down load as a GIF Image. Its name is Triangul.GIF.
If the signal is a malicious or otherwise illegal signal, these second and following stake out locations should be chosen so as to not be visible to persons traveling roads into or out of the suspect area. You don't want to tip off the Bad Guy.
Jump to articles: Spiral-In Hunting Technique -- Catch A Jammer -- Safety
George R. Andrews (Russ, K6BMG) BMG Engineering, Inc. 9935 Garibaldi Avenue Temple City, CA 91780, USA Voice: 1(626)285-6963 FAX: 1(626)285-1684 (24 Hour, automatic) America OnLine: Grandrews Web: http://members.aol.com/bmgenginc (31 Jan 1996)
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