Radio Direction Finding Scott Honaker N 7 SS

Radio Direction Finding Scott Honaker N 7 SS

Why do we need these skills? ► Locating § § § Jammers Stuck transmitters Local noise sources ► Search § § § Harmful Interference and Rescue ELT/EPIRBs FRS/ham radios Wildlife location ► Navigation Scott Honaker - N 7 SS 2

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 - N 7 SS 3

Equipment ANTENNAS Scott Honaker - N 7 SS 4

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 - N 7 SS 5

Beam/Yagi ► Very accurate bearings ► Requires clean pattern and good front-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 - N 7 SS 6

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

Equipment ADVANCED EQUIPMENT Scott Honaker - N 7 SS 8

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 - N 7 SS 9

“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 - N 7 SS 10

Theory LOCATING THE FOX (TRANSMITTER) Scott Honaker - N 7 SS 11

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 - N 7 SS 12

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 - N 7 SS 13

Advanced Tools ► Excel + geofunc http: //www. afsc. noaa. gov/nmml/software/e xcelgeo. php ► Mapping Tool – Streets and Tips, Map. Point, Street Atlas ► GPS System Scott Honaker - N 7 SS 14

Sources of Error ► Operator Error ► Antenna Gain Pattern ► Propagation § Multi Path § Reflection Scott Honaker – N 7 SS 15

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 2 m beams are unwieldy, omnis offer some info while driving Scott Honaker - N 7 SS 16

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 - N 7 SS 17

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 (2 m 3 rd harmonic on 70 cm) § Be aware of local multipath sources Scott Honaker - N 7 SS 18

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. html Scott Honaker - N 7 SS 19