Homebrewing UHF Yagi

Homebrewing UHF Yagi

I had built a seven element VHF Yagi some time back. Now I am planning to build a UHF Yagi. I got a design by VU2AAP from the October 2022 issue of QSP magazine. The basic design was of a seven element UHF Yagi, primarily meant for amateur radio satellite communication. In my region there is no UHF repeater, with the nearest one at Bengaluru being about 277 km away. So my aim of building this Yagi is to enhance my UHF reception capability during amateur radio satellite operation, which has been quite low with the current CP22E vertical antenna. Neverthless, I was able to have a few contacts through V/U satellite transponders like International Space Station, Tevel 7 and Tevel 3. When I had attempted using the V/U transponder on Saudisat 1C, my VU freinds told me that though they are able to hear my call, I am not hearing their replies.

I found that the surplus one inch square aluminium boom which I had, can hold an eight element Yagi. So I marked out the locations on the boom for the elements and thought of asking VU2AAP for the length of the 8th element. He told me that 7th and 8th elements and any more could have same length and spacing. Still, he strongly advised me to go for a 5 element Yagi initially for a broader beam width. As I was a beginner in the field of amateur radio satellite communication, my mentor felt that it will be quite difficult for me to point the antenna correctly, if I go for one with more elements and a narrower beam width. He told me that leaving the remaining length of the boom like that will do no harm, leaving space for potential future expansion.

In the first stage of the antenna building, I have used a hacksaw, steel measuring tape and a steel scale. A pencil was used to mark out the measurements on the boom and the 3/8 inch aluminium pipe to be cut. A few small wooden blocks in the store were used while using the hacksaw, to prevent damage to the surface of the table. After cutting out the elements, a 5 cm piece of 3/8 inch aluminium pipe was cut for the Gamma matching rod. Spacing between the Gamma rod and the driven element was given as one inch. So I measured out 2.5 inch of one inch square aluminium pipe to be used as Gamma shorting stub, which will have sufficient space on either side when holes are drilled for the driven element and Gamma rod. Tomorrow I will have to visit the nearby hardware shop to get powder coated clamps, PVC T connector and screws needed to fix the clamps on the elements.