6 Meter Homebrew Yagi Tunes Up! Hooray!

6-meter yagi from below on mast
The 6-meter Yagi at full height
With the impetus of several suggestions from the QRZ Forums Antennas group, I made a great leap forward in tuning up the homebrew 6-meter Yagi. First things first, I replaced the test cable to the AA-54, which had an intermittent short or open in one connector. I made a longer cable so that I could step out of the antenna's immediate shadow and used bigger ferrites for the choke on the cable. While I was waiting for the PL-259 to cool down, I made a quickie 5 turns coax choke on a 3" form too.

I discarded the few turns through a 2" ferrite choke on the antenna feed line and inserted the 3" choke. Already the disparity between the SWR R/X readings on each end of the feed line was vastly reduced. I went back to adjusting the gamma match again and when I had it to an acceptable range, I decided to pull up the antenna mast to full height, which I can do single-handedly thanks to my counterweights at the bottom of the mast.

antenna analyzer showing SWR of 1.01I didn't have to await my reward in heaven today as the SWR improved at full height to an almost perfect state: a 1.02 SWR at 51.102. I'm not touching that!

This whole VHF antenna adventure has demonstrated to me just how touchy things can get at short wavelengths. It also required that I refurb my "experimental" mast, which I had neglected for over a year after it was bent in a high wind due to a guy failure. I had to cut out a meter of the mast tube and re-weld the pieces. I removed the old modified VK2ABQ, which was pretty weathered by this time.

SWR graph of homebrew 6 meter antennaThe electric winch was weather worn also, so it was dismounted and I dismantled it on the workbench. Besides some general cleaning out and a little de-rusting, I noticed that the carbon brushes weren't so springy anymore. Turned out that three of the four brush springs were either missing or crumbled due to corrosion. One still had some life in it. I started searching my junk drawers and the first place I looked I found, not one, not two, not four, but exactly three springs of the same length and diameter! They've probably been waiting over 10 years for their moment to stand in the sun, ... so to speak!

I don't plan on leaving the winch out in the weather anymore, so I had to make a small modification to its connection to its plate so that I can leave the plate and easily detach/attach the main winch when I need it. Everything got a good cleaning and a fresh caot of paint too.

The rotator also got a going over but it's not connected yet. So, the Yagi is fixed at due north for now. Tomorrow I'll get down to dealing with the rotator and finishing the weatherproofing of all connections (I prefer a final coat of roof leak tar, it really stands up to the tropical climate) and re-installing the winch for a test run. Then, I begin learning about how 6 meters really works!

No comments:

Post a Comment

Thanks very much for your comment! 73, Casey