NRHARC Fox Hunting
Also Known as RDF (Radio Direction Finding)
Next Fox Hunt TBD Stay tuned for details!
NRHARC Hidden Transmitter Hunt
Rules for the NRHARC Hidden Transmitter (hunters should know these rules, too!)
1. The hidden transmitter site must be on public land (parks, schools, etc.), visible and accessible by a vehicle using public roadways. You cannot hide on a boat out on a lake and cannot hide on the roof of a public building.
2. You must hide within the limits of NE Tarrant Co. It is best to obtain the Mapsco NE Tarrant Co map.
3. Hunters start from the NRH Fire Administration Building, 7202 Dick Fisher Drive, NRH. You must make a reasonable effort that receiving stations will hear you from the starting location.
4. Select a site well in advance and make a plan. Consider that you may need to pull an antenna into a tree to get a high profile. Be set up and ready to transmit ahead of the start time. Start on time; the hunters will be waiting. At the start, ask the number of hunters – that will come in handy later.
5. Buy refreshments and serve once the hunters arrive. Keep the receipt up to $15 to turn into the club treasurer.
6. Your antenna must be omnidirectional, but any power level is OK (see also #3 above).
7. Transmit continuously on 146.460 MHz until found. This reduces the risk of reckless driving. Read a QST article or anything you like; periodically announce that you are the hidden transmitter. ID every 10 minutes as required. Once most hunters have arrived, reveal your location to stragglers.
Rules for Hunters
1. Obey traffic laws and drive safely. Stay on public roadways. Since you can get a directional bearing anytime, take the time to pull off the roadway and out of traffic when taking a bearing.
2. Doppler shift technology is not permitted – that would take the fun out of it.
3. If you are first to arrive at the hidden transmitter location, you set the date and hide next month.
Hints for Hunters
1. Use a directional antenna. Use a receiver with an S-meter, analog S-meters are easier to read.
2. Take a map of Tarrant County – note that parks are usually identified in green color.
3. Take a partner to hold the antenna while you focus on driving safely. If you can, take two partners, one for the antenna and one to study the map and take bearings.
4. A hand-made 3 element beam or Cubical Quad is cheap, easy to make and they work great. Watch for low hanging branches.
5. As you get closer, the signal will be full scale in any direction. Use an attenuator to reduce the signal and center the S-meter. If no attenuator, DF when really close by removing the antenna from your HT and rotate the HT on a flat surface (practice this on a known signal ahead of time). If you use an attenuator, don’t TX into it.
6. Technique #1 – drive toward the transmitter taking regular bearings until you arrive
7. Technique #2 – drive some distance at right angle to your first bearing and take a second bearing. Triangulate and estimate the location of the hidden transmitter and drive there.
8. Try to take your bearings on high ground, but away from metal reflectors (like water towers). These locations are more likely to give you an accurate bearing.
Fox Hunting (RDF) sites:
http://www.homingin.com/
http://www.dxzone.com/catalog/Operating_Modes/Radio_Direction_Finding/
440 Tape Measure Beam (click for PDF file)
2 M Beam: http://www.arrl.org/files/file/Technology/tis/info/pdf/9304054.pdf
Tape Measure 2M Beam:
http://theleggios.net/wb2hol/projects/rdf/tape_bm.htm
Cubical Quad plan: http://www.hamuniverse.com/3el2meterquad.html
Easy driven element:
http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=12570
This shows an easy way to feed the driven element without using a gamma match:
Attenuators
Build your own: http://www.arrl.org/files/file/Technology/tis/info/pdf/9506033.pdf
http://www.homingin.com/joek0ov/offatten.html
http://www.w9dup.org/club_projects_pdfs/attenuator_project_2010_may.pdf