Component lists for RDF Antennas and Equipment
August 2006
www.NRHARC.org
Items needed for a fox hunt (Radio Direction Finding):
Radio or other RF detector, our fox hunts will be on 2 meter band (VHF/UHF dual band useful)
Antenna, ideally one long range and one short range (beam for long range, loop for short)
Attenuator, dissipative or offset
(TDOA units below replace all 3 and are primarily short range finders)
The material lists below are based on the plans distributed earlier this year. Some of these are in
the ARRL publications, Handbook or Antenna book. The book by Joseph Moell and Thomas
Curlee “Transmitter Hunting Radio direction Finding Simplified” is the standard reference on the
subject. (ISBN 0830627014)
More attenuator designs are in almost every ARRL Handbook. Precision resistive attenuators
will work but are not necessary. A resistive attenuator with coarse 10 or 20 dB steps would
work. The most important factor when using an attenuator is that the receiver or other RF
detector obtain all the signal through the attenuator. If RF gets into the receiver around the
attenuator, that becomes the system performance limitation.
Some of the designs listed below are a weekend project and require more than an hour or two to
complete. While assembling these projects you will learn some about electronics, RF
construction techniques, antenna performance, and RF detection techniques.
General notes on the lists below:
All 50 Ohm coax can be low loss types. For longer runs, use lower loss or types larger than RG58/U or RG-8X.
The matching sections using RG-59/U must be 75 Ohm solid dielectric type. Using 50 Ohm
coax as a substitute is not acceptable.
For mounting components, blank pc board material can be used as a ground plane.
Perf board provides an array of holes for mounting, but does not have a ground plane.
RF chokes for VHF are several turns of small copper wire on a 100k Ohm or greater quarter-watt
carbon composition resistor.
Capacitors 1 uF or greater are Tantalum or aluminum electrolytic 25V or higher. Tolerance is
not critical.
Capacitors less than 1 uF are ceramic 25 or 50 volts, 10 or 20 % tolerance is acceptable.
PVC pipe, clamps, screws, and other hardware items are at all hardware stores.
Electronic components are at Radio Shack, Jameco, Mouser, or Digikey.
Antennas:
From Moell and Curlee “Transmitter Hunting – Radio Direction Finding Simplified”
Fig. 4-1 Simple 2 meter loop
36 inches solid copper wire #12 or #10
1 small alligator clip to fit above wire
1 x 1 inch minimum epoxy board (pc board) or perf board
1 trimmer capacitor 1 to 10 pF – glass or ceramic
24 to 48 inches wood or plastic rod, 3/4 inch to 2 inch dia. (circular, square, rectangular, or PVC
pipe, 1x2 or 1x4 inches wood)
3 to 6 feet coax cable 50 Ohm (RG-58/U, RG-8X, etc.)
connector for your radio
nylon wire ties
From Moell and Curlee “Transmitter Hunting – Radio Direction Finding Simplified”
Fig. 4-13 Coax phased array
7 feet solid copper wire #10 or larger, 4 pieces 21 inches (or brazing rod, Al rod, 3/16 to 1/4 inch
dia., or old TV antenna elements)
a method to attach coax conductors to these pieces – need 4 – screw clamps, small hose clamps if
Al (solder will work for brazing rod or copper wire)
2 pieces coax, one 48 inches, second 3 to 6 feet, 50 Ohms
connector for your radio
22 to 36 inch long board 1x2 or 1x4, approximate dimensions
nylon wire ties
optional: handle – 6 to 8 inches or longer wood rod ¾ to 2 inch dia.
From Moell and Curlee “Transmitter Hunting – Radio Direction Finding Simplified”
Fig. 4-15 ZL special
8 feet PVC pipe ½ to 1 inch
3 tee
2 elbow
2 cross
1 foot 300 Ohm ladder line
7 feet 450 to 600 Ohm ladder line
nylon tie wraps
48 inches RG-59/U 75 Ohm coax – solid dielectric, not foam
4 to 10 feet RG-58/U or RG-8x (mini-8)
connector and/or adapter for your radio
Tape measure beam from http://home.att.net/~jleggio/projects/rdf/tape_bm.htm
4 to 10 feet 50 Ohm coax, connector, adapter
5 inches #16 to #18 wire copper
6 hose clamps to fit over crosses and tees together with antenna elements
3 PVC cross
2 PVC tee
3 feet ½ to ¾ inch PVC pipe
36 inch element, stiff rod, aluminum or copper, tape measure, or old TV antenna rod
43 inch element, stiff rod, aluminum or copper, tape measure, or old TV antenna rod
2 each 20 inch elements, stiff rod, aluminum or copper, tape measure, or old TV antenna rod
4 #6 solder lugs
2 each #6 x 3/4 inch screws and nuts
nylon wire ties
2 meter half-wave J pole
42 inches #16 or #18 stranded or solid Cu wire
20 inches 450-600 Ohm ladder line 16 to 18 gauge
2 nylon wire ties
6 to 30 feet 50 Ohm coax
connector for your radio
Broomstick antenna from http://home.mesh.net/Lilburn/instructions/
24 inches 1x2 wood
2 each 20 inch long Al rod 3/16 dia or equivalent (#6 or larger copper wire)
6 tie wraps 5.5 inch long
wood screw #10 x 1.5 inch long
48 inches RG-59/U 75 Ohm coax – solid dielectric, not foam
nylon wire ties
50 Ohm coax and connectors to connect to attenuator and radio
mop handle or broom stick – wood ¾ to 1.5 inch dia
optional: to make coax connections neater, use components below:
brass strip 3.4 x 12 inches .040 thick
2 connectors type F for RG-59
2 connectors type F female panel mount
connector BNC panel mount female
2 sheet metal screws #8 x 3/8 inch long
3 element 2m beam from ARRL Antenna book Fig. 20.103 page 20.59
7 feet min ¾ to 1 inch PVC pipe
1 PVC Tee
elements: solid copper #10 or larger, 3/16 to ¼ inch dia, brazing rod, aluminum rod, or old TV
antenna elements
2 pieces 24 inches
1 piece 35 inches
1 piece 40 inches
2 screw wire clamps or small hose clamps
2 of a method to attach coax conductors to the elements – screw wire clamps or small hose
clamps if aluminum, or solder will work for copper or brazing rod
more screw clamps or small hose clamps if aluminum rods need to be spliced
4 to 10 feet 50 Ohm coax
connector for your radio
optional: modifications to make it foldable for storage:
8 hose clamps or screw wire clamps to hold antenna elements in PVC pipe
3 screws and nuts to connect PVC pipes to Tees
nylon wire ties
Time Difference of Arrival units combine antenna and detector in one package:
Deluxe TDOA “The Simple Seeker” from ARRL Handbook
PVC pipe 10 feet min, ½ to 1 inch (better 15 feet)
3 Tee
3 each 1.5 inch long cotter pin (or #6 to #8 screws and nuts)
9 feet #12 or #10 solid copper wire or other antenna element material
(option: 2 each helical rubber duck antennas and 2 BNC M-F elbow, omit PVC pipe and above)
CMOS 555 Timer IC LMC555CN
3 x 4 inch (approx) pc board or perfboard
aluminum box approx 4 x 6 x 2 inch, capable of good RF shielding
2 PIN diodes NTE-555 or Motorola/On Semi MPN3404
(acceptable substitute diodes 1N4148)
8 feet RG-58/U or other 50 Ohm coax
2 each 470 Ohm ¼ W
3 BNC cable male connectors
2 BNC panel mount female connectors
9V battery and connector and battery holder if desired
2 SPDT switch
switch DPDT
headphones (mono or stereo)
2 connectors for headphones
470 pF cap 25V
4 each 4.7k Ohm ¼ W
2 each 22 uF 25V
100k ¼ W
220k ¼ W
100k pot
0.01 uF 25V
4.7 uF 25V
Meter 100-0-100 uA
2 each 1N4148 diodes
audio transformer 1:10 stepup CT secondary
4 each 10 Ohm 1W resistor
25 Ohm 2W variable resistor
nylon wire ties
Switching direction finder TDOA from http://www.geocities.com/Yosemite/trails/4024/
4 diodes 1N914 or 1N4148
2 each 680 pF caps 25V
2 each 470 Ohm ¼ W
4 RF choke 12 uH, 10 inches copper wire #22 to #26 on 100k Ohm or greater ¼ W
4 each ¼ wavelength antenna elements (19 to 20 inches at 144-148 MHz)
4 clamp connections if not solderable (screw wire clamps)
24 inches 1x2 inch wood
mop handle or broom stick – wood
wood screw #10 x 1.5 inch long
copper ground plane or perf board to mount components 2x2 inch square min.
5 to 6 feet coax 50 Ohms
connectors for your radio
0.1 to 0.5 uF ceramic 25V
22k Ohm ¼ W
10k Ohm ¼ W
0.05 uF cap 25V
switch SPDT
9V battery and connector and battery holder if desired
(need 7805 regulator or 3 AA cells if using HC inverter)
inverter IC 74C14 or CD4069 (supply to 15V) or 74VHC14 or MM74HC04 (supply 6V max)
aluminum box if desired
nylon wire ties
TDOA from http://www.hcarc.com/events/Fox-Hunt/Fox-Hunt.htm
CMOS 555 timer IC LMC555CN
4.7k Ohm ¼ W
100k Ohm ¼ W
2 each 470 Ohm ¼ W
0.01 uF 50V
10 uF 25V tantalum
0.01 uF 50V
0.001 uF 50V
2 PIN diodes MPN3404
RF choke, 8 turns #22 to #28 wire on 100k Ohm or greater carbon 1/4 W resistor
Switch SPDT
Pc board or perf board 2 x 4 inches min.
9V battery and connector and battery holder if desired
solid copper wire #10 to #14
broom handle or 1 x 2 inch wood, approx. 24 inches or more
3 to 6 feet RG-58/U coax (longer if handle is longer than 6 inches)
BNC connector for your radio
nylon wire ties
Attenuators:
Offset attenuator #2 from http://www.southgatearc.org/articles/attenuator.htm
pc board or perf board 1 x 2 inches min.
2 connectors BNC panel mount female
2 each 470 pF 25V min
diode 1N4148
2 each 2.2k resistors ¼ watt
pot 5k audio taper and knob
4.7k 1/4w resistor
4.7 nF 25V cap
switch SPDT
9V battery and connector and battery holder if desired
7805 IC 5 volt regulator
4 MHz oscillator (2 MHz also works)
aluminum box 3x2x1.25 minimum (larger ok, big enough to fit pots and connectors)
Screws to mount connectors and close box
Dual pot attenuator from http://home.mesh.net/Lilburn/instructions/
2 BNC panel mount connector female
2 pots 500 Ohm
2 knobs
resistor 100 Ohm ¼ watt
aluminum box 3x2x1.25 minimum (larger ok, big enough to fit pots and connectors)
Screws to mount connectors and close box
Offset attenuator from http://home.att.net/~jleggio/projects/rdf/a_atten.htm
Aluminum box (min) 1.5 x 2 x 1 inches
6 inches #22 solid copper wire (to make 3.3 uH choke) 100k Ohm or greater ¼ W
2 BNC panel mount connectors
2 AA cell holder
2 AA cells
switch SPDT
0.047 uF 25V
1k Ohm ¼ W
2 each 150 pF 25V
22 pF 25V
1.8 Meg Ohm ¼ W
1N914 diode
4.7k Ohm ¼ W
MPF102 FET
1 MHz XTAL
1k pot and knob
Offset attenuator from http://www.qsl.net/nz0i/projects/attenuator/attenuator.html
9V battery and connector and battery holder if desired
10 uF 35 V Tantalum
3 each 100 pF 25V
5 each 1N4148 diode
3 each 100-ohm ½W
10K-ohm Linear Taper Potentiometer with knob
2 each 1K-ohm ¼W
82-ohm ½W
DPDT Switch
7805 5-volt Regulator
4MHz Oscillator (2 MHz also works)
aluminum box 3x2x1.25 minimum (larger ok, big enough to fit pots and connectors)
Screws to mount connectors and close box
2 BNC Female Chassis-mount Connectors
BNC Double-male Adapter
Copper ground plane or perf board to mount components