2 m Fox Hunting Antenna

Electronics, Orienteering,

This article describes a Yagi antenna I have designed for use in a “fox hunting” receiver for the 2 m band (144 MHz). The antenna uses 25 mm wide steel tape measure for the elements, 16 mm PVC pipe as the boom and 3D-printed parts to keep it all together. Models for the 3D-printed parts are available for download.

Link to a zip-file with 3MF models of the parts:


[ZIP]

Several Yagi antenna designs for the sport of fox hunting (or ARDF, amateur radio direction finding) have been published and can be found by some searching on the web. I decided to have a go at designing such an antenna myself and used the free YagiCAD program to do so. After a number of rounds of optimization starting from different base designs, I ended up with the following:

Antenna dimensions [mm]

The shortest element is the director (towards antenna main lobe) while the longest is the reflector. The “driven” element is the one in the middle.

According to YagiCAD, the radiation pattern of the antenna is as follows:

Simulated antenna radiation patterns at 144.75 MHz

Front-to-back ratio is simulated to be above 40 dB.

While I have not measured the real antenna diagram, the subjective assessment is that the antenna performs well. Using a network analyzer, I have found that it’s impedance is around 40 -j0 ohms at 145 MHz.

For the beam, I used a piece of 16 mm outside diameter PVC electrical conduit pipe (“VP-rör” in Swedish).

For the elements, I used 25 mm wide steel tape measure from Biltema, e.g. part number 16-2931.

To mechanically connect the elements to the beam, I designed various clamps that I printed on my 3D printer. The antenna needs to be made smaller for storage and transportation, so I also designed spools and clamps to allow the elements to be rolled up and kept securely in that state. Furthermore, I have designed a handle that can grip on the pipe and be secured by a screw pulling a wedge. Pictures of all these parts are shown below.

Clamp for director and reflector. Requires M3 screws and nuts.
Clamp for driven element, including a strain relief (red) for an RG174 coax and some sideways adjustability of the elements for tuning. Requires a few M3 screws and nuts.
Another view of the clamp for the driven element. Note the slots in the green part that allows the length of the elements to be adjusted by a few mm.
Spool for rolling up an antenna element. The spool consists of two halves that need to be glued together, a 5 mm long M2.5 screw and a removable center pin that helps while rolling up the element. One pin can be used for all six spools.
Antenna spool with a clamp (red) that secures the rolled-up tape measure (not shown). Note the peg on the red clamp that fits in one of the notches on the spool (to the right in this picture) to prevent the whole thing from unrolling.
One half of the spool. There are three holes where short pieces of filament can be inserted to help with alignment during glue-up and to make the glue-up stronger.
The end of each antenna element needs to be chamfered at a shallow angle and a 3 mm hole has to be made to fit in the M2.5 “hook” inside the spool. The sharp cut edges can be made less dangerous by putting sports tape over them.
Complete handle
Handle without the clamp, showing the wedge and screw.
Cross section of handle, showing the wedge, screw and knob that pulls on the wedge to secure the grip on the pipe.
Complete receiver
Receiver ready for storage or transportation with rolled-up elements and the handle folded to the side
Close-up of antenna elements rolled-up on spools with clamps holding them in place

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