1 / 19

Radio Direction Finding

Radio Direction Finding. Scott Honaker N7SS. Why do we need these skills?. Locating Harmful Interference Jammers Stuck transmitters Local noise sources Search and Rescue ELT/EPIRBs FRS/ham radios Wildlife location Navigation. Equipment Needed.

kristopher-tannis
Download Presentation

Radio Direction Finding

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Radio Direction Finding Scott Honaker N7SS

  2. Why do we need these skills? • Locating Harmful Interference • Jammers • Stuck transmitters • Local noise sources • Search and Rescue • ELT/EPIRBs • FRS/ham radios • Wildlife location • Navigation Scott Honaker - N7SS

  3. Equipment Needed • Radio receiver and antenna that are directionally sensitive and can receive the signal • A way to determine your direction • A map and compass would be nice Scott Honaker - N7SS

  4. Equipment Antennas Scott Honaker - N7SS

  5. Wire Antenna • Simple • Signal strength only • Directivity via body blocking • Works better with stronger signal and well shielded receiver • High skill level required Scott Honaker - N7SS

  6. Beam/Yagi • Very accurate bearings • Requires cleanpattern and goodfront-to-back ratio • Easily overloaded by strong signals • Tune to null (sharper than gain) • Can use front to help find weaker signals but with reduced bearing accuracy Scott Honaker - N7SS

  7. Loops • More common on HF frequencies • Very compact • Tune to the null • Bearings not very precise • Has 180 degree ambiguity Scott Honaker - N7SS

  8. Equipment Advanced Equipment Scott Honaker - N7SS

  9. Adcock Device – Handi Finder • Based on phase difference • Antenna array MUST be symmetric • Can’t identify front/back without a third sense antenna • Tune to no tone (signals in phase) • Weak signals can be a problem • Strong signals may cause too much multipath Scott Honaker - N7SS

  10. “Doppler” DF – DF Jr. • Not real Doppler – uses a pair of Adcock antennas • Gives real-time bearings • Only accurate to~30 degrees • Antenna size and spacing are frequency dependant Scott Honaker - N7SS

  11. Theory Locating the Fox (transmitter) Scott Honaker - N7SS

  12. Triangulation • Doing the Math • α, β and distance AB are already known • C can be calculated by using the distance RC or MC: • RC: Position of C can be calculated using the Law of Sines • RC or MC can be calculated using the Law of Cosines and the Pythagorean theorem Scott Honaker - N7SS

  13. Triangulation • Graphical Approch • Take bearings from three points • 90% of contacts will be inside intersecting triangle • Don’t neglect signal strength info • Signal strength will depend on terrain Scott Honaker - N7SS

  14. Advanced Tools • Excel + geofunchttp://www.afsc.noaa.gov/nmml/software/excelgeo.php • Mapping Tool – Streets and Tips, MapPoint, Street Atlas • GPS System Scott Honaker - N7SS

  15. Sources of Error • Operator Error • Antenna Gain Pattern • Propagation • Multi Path • Reflection Scott Honaker – N7SS

  16. Foxhunting • Containment Area • Large (county) vs. small (city) or local (park) • Drive times become significant • Starting location • Together vs. distributed • Radios/antennas • HTs vs. mobiles • HTs offer portability but mobile meters are often more accurate • Omni vs. beam • Even 2m beams are unwieldy, omnis offer some info while driving Scott Honaker - N7SS

  17. RDF Techniques • Mapping • Time vs. accuracy • Accurate bearing plotting is time consuming but often valuable • Terrain • Multipath issues – particularly in urban areas • Reflections can mislead and can be accentuated if the target uses a directional antenna Scott Honaker - N7SS

  18. RDF Techniques • Going the last mile • Attenuators for non-Adcock antennas • Removing the antenna when within a couple blocks • Body blocking • Detuning decreases receiver sensitivity • Tune a harmonic (2m 3rd harmonic on 70cm) • Be aware of local multipath sources Scott Honaker - N7SS

  19. Resources • Homing In Site http://members.aol.com/homingin/ • Tape Measure Yagi http://home.att.net/~jleggio/projects/rdf/tape_bm.htm • Adjustable Attenuator http://home.att.net/~jleggio/projects/rdf/p_atten.htm • Arrow Antenna http://www.arrowantennas.com/ • Ultimate Automated Doppler DF System http://www.ahha-doppler.com/gpss/gpss.html Scott Honaker - N7SS

More Related