What Is RDF? (aka "Transmitter-Hunting", aka "Fox-Hunting")
What Equipment do I Need ?
About YRARC Fox-Hunts
Links to Transmitter-hunting-related Websites
Build your own TDOA Direction Finder !
Radio-direction-finding (RDF), also called transmitter hunting or"fox"-hunting,
is a method of using radio-direction-finding techniques to find the location
of a radio transmitter.This facet of Amateur Radio has both a serious and
a fun side (neither of which involve the pursuit of any furry woodland
RDF techniques have been used by Amateurs to locate sources of radio-frequency
interference (RFI), unintentional or otherwise, to Amateur Radio and other
radio services, such as municipal fire department and law enforcement radio
communications systems. In the US, RDF-equipped Amateurs are available
to help authorities locate downed civilian aircraft in rugged terrain by
tracking the aircraft's ELT (emergency locator transmitter).
"Fox"-hunting, on the other hand, is a recreational activitywhere a
group of Amateurs use their RDF equipment to locate one or more oftheir
members (the designated "fox"es) who are transmitting fromsecret locations.
Fox-hunting is both great fun and good practice for honingone's RDF skills.
T-hunting, a popular sport in Europe and Asia, combinesorienteering and
RDF. Participants, equipped with a map, compass,radio receiver and directional
antenna, compete to locate small automatictransmitter beacons, usually
hidden in a wooded area, as quickly as possiblebefore racing to the finish
line. Total score is based on elapsed time and number of transmitters found.
What equipment do I need ?
The equipment required to participate in fox-hunting can range from very
simple to fairly exotic. Most fox-hunts in this area occur on 146.565 MHz,
in the 2-metre Amateur band, simply because most amateurs own a 2-metre
hand-held transceiver. Directional antennas for this band are reasonably
small and portable enough to use for tracking on foot or from a vehicle,
and are easy to build. Other RDF equipment that can be easily constructed
at home include directional antennas, signal-strength meters (RF-"sniffers"),
TDOA (time-difference-of-arrival) antennas (build
your own!), and RF attenuators. Doppler DF units, handy for mobile
fox-hunting, can be bought as kits or complete units. Please note that
an Amateur Radio licence is not required if you wish to participate as
a hunter, since only a receiver is really necessary.
The York Region Amateur Radio Club
(YRARC) holds informal fox-hunts from late May throughto late August,
generally on a Tuesday, Wednesday or Thursday evening, every week or two,
determined by a concensus of the regular participants. Starting location
(for the hunters) is the south-west corner of the 404 Plaza parking lot,
between Harvey's and Tim Horton's. Start time is 7:00PM, but the hunters
should show up 10 - 15 minutes earlier to pick teams, check their gear,and
check-in with the hunt co-ordinator. Hunts usually involve both mobile-
and foot-tracking, sometimes through fields or woods, so appropriate footwear
is essential. Each fox will transmit periodically, and will usually begin
giving (progressively more specific) clues to his/her location as it begins
to get dark. The hunt is usually closed by 9:00PM or earlier if it's too
dark to hunt. An informal fox-hunt debrief is then held at the nearest
convenient establishment serving coffee and doughnuts. The winner (most
foxes found thequickest) gets to be the fox for the next hunt.
Interested in attending a "fox"-hunt in the Newmarket area ?
Contact Bill Griffith, VE3WGX (email : firstname.lastname@example.org
or email@example.com )
Links to Transmitter-hunting-related sites
WB6EYV - Bob Simmons' Doppler
DF ( and how it works ... )
- build it yourself, or inquire about PCBs, kits, or assembled &
VE2EMM - the Fox-hunt
homepage of Jacques Brodeur
also ...VE2EMM's Fox-hunting Freeware Homebrew Projects index
N2KI and W2KI's Fox-hunt
Web-page - lots of projects and links!
- Several Do-it-Yourself RDF Projects (including a TDOA , tape-measure
antennas, simple fox transmitters!)
K0OV - Joe Moell's
"Homing-In" Page (see his monthly column in 73 magazine)
K6BMG - BMG Engineering,
Radio Direction Finding, RDF, T-Hunt, Fox Hunt
N6BG - Hidden Transmitter
Robert Barris's RDF Page
Radio Direction Finding
- Dopplers by Ed Greany, KB6DOL
Hamlinks - more RDF links ...
list of Amateur Radio Direction Finding (RDF) Companies
Updated 07 Apr 00