Universal DIY Carbon Yagi Antenna - for only 20€
At the end of December 2015, I build a QFH antenna out of PVC pipe and wire for the 2m band (~137mhz). That antenna was great to receive NOAA and MeteorM2 satellites, but it struggled when I was not at the open field. In mid 2016 I bought a cheap Yagi from eBay for the 70cm band to receive for instance the SO-50 amateursat. I was blown away by the performance of that cheap Antenna and searched for a 2m Yagi that I can buy or build myself.
After some study I decided that I was not willing to pay around €130 to import a Arrow antenna from the US and instead build one. I found the "7db for 7 bucks" PDF online that is quite old, but a brilliant design. The first antenna was out of PVC pipe and welding rod, what worked but was neither pretty nor very stable. The PVC pipe was so unstable that it flexed when I was holding it in the air to receive a signal. That also resulted in very strange signal artefacts that were really bad.
After I got a 3D printer in October, I begin to design an antenna in the CAD Software Fusion360 that uses the same "7db for 7 bucks" principal for the 2m band. My main goals were that the Antenna was stiff but also very lightweight. Because of that, the main boom of the antenna is out of carbon fiber pipe with a diameter of 12mm. The 3d printed parts clamp on the carbon fiber with clamps out of aluminium that are inserted in the plastic. Also, the clamps allow me to fold the Antenna in half for transport, what is really nice, because otherwise it wouldn't even fit in my car without a hassle. The receiving Elements are made from welding rods with a diameter of 2mm like before, that are inserted through the 3d printed parts and held in with hot glue (can be any glue). The cable from the feeder can be routed through a hole in the plastic part and the carbon tube so it comes out at the bottom of the Antenna.
All these parts only cost you around 20€ depending on where you get them from. I got the carbon pipes and aluminium clamps from Aliexpress (China) and the welding rods and cable from eBay (Germany). But the Results are stunning! I got over 36db SNR at a NOAA18 pass with a max elv. Of only 34° out of my backyard with a RTl-SDR.com v3, FM Trap and LNA4All. over 36DB! I think that is really awesome for such a cheap Antenna that is made in a few hours (incl. 3d printing).
Because the frequency of the Yagi is set with the length of the Elements and the distance between the Director, Feeder and Reflector, design can be built for almost any frequency. You just have to calculate the lengths according to the instructions in the "7db for 7 bucks" PDF.
You can get the 3d printable files, a list of items you need and instructions on Thingiverse
I also made two YouTube Videos. The first one is about the build and the second is a test of the Antenna.