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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.

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radio direction finding

Radio Direction Finding

Scott Honaker

N7SS

why do we need these skills
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

equipment needed
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

antennas
Equipment Antennas

Scott Honaker - N7SS

wire antenna
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

beam yagi
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

loops
Loops
  • More common on HF frequencies
  • Very compact
  • Tune to the null
  • Bearings not very precise
  • Has 180 degree ambiguity

Scott Honaker - N7SS

advanced equipment
EquipmentAdvanced Equipment

Scott Honaker - N7SS

adcock device handi finder
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

doppler df df jr
“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

triangulation
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

triangulation13
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

advanced tools
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

sources of error
Sources of Error
  • Operator Error
  • Antenna Gain Pattern
  • Propagation
    • Multi Path
    • Reflection

Scott Honaker – N7SS

foxhunting
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

rdf techniques
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

rdf techniques18
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

resources
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

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