I already built a somewhat portable YAGI some time back, but when I am honest to myself, it’s not portable at all. I mean you can disassemble it but it is big and bulky and heavy. Not suitable for SOTA.
Also, the common mode choke, or better said, an ugly balun wound with RG174 is a big loss factor for VHF. In the end, that antenna was only used once and the materials scrapped for other projects.
This time I used a very small boom and 4mm aluminum rods that are not eloxated. For clamping the elements together I had a ingenious idea. Using the clamps for electrical wires, take out the metal part and design a suitable casing for 3d printing. It works!
The design is from:
for the 1m boom and 28 Ohm match. According to DK7ZB, 28 Ohms is the best choice for bandwidth and good propagation lobes. I used exactly the same measurements described in the text for 4mm and have a perfectly resonant antenna on 145.500. The bandwidth is enough to go for the SSB part on VHF on SWR around 1.3 to 1.4. For VHF that is really good, considering the rubber ducks go to SWR of 2 or higher.
To secure the clamps on the boom, use M4 screws with nuts that can be hand tightened or with a small plier. You also need 2x 34.5cm of 75Ohm Coax for the matching. You can additionally connect the GND of the connector to the boom, it should help to reduce the common mode current.
To attach the wires to the radiator, I used 2 cableshoes that slide in the connecting clamp and you can then solder on them. For the 75Ohm coax shield use some clamps that can be soldered, since the shielding does not accept solder.
You can download the files for printing here:
Enjoy and let me know what you think!