Bible
Verse
Philippians 3:7-8 But whatever was to my profit I now consider loss for the sake of Christ. What is more, I consider everything a loss compared to the surpassing greatness of knowing Christ Jesus my Lord, for whose sake I have lost all things. I consider them rubbish, that I may gain Christ. (NIV)
President’s Report
We will not have a MARC business meeting this Saturday. Please join us for breakfast and fellowship.
KB6NU builds an end-fed, half-wave antenna
I’ve always been interested in end-fed, half-wave antennas before, but until this recently, I’d never built one. One of the reasons for this is that most designs are for QRP antennas and not made to handle more than 5 – 10 W of power.
A couple of months ago, though, I ran across a design rated at 100 W (http://earchi.org/proj_homebrew.html). The design seemed relatively simple to build, requiring only a single toroid and a capacitor made with a short length of RG-174 coax. Well, it just so happens that I bought 100-ft. of RG-174 at Dayton this year, and I found the toroid cores online from the "Toroid King" for a very reasonable price, so I decided it was high time to build one.
All told, the parts cost about $10, the biggest part of that being a 4-in. x 4-in. x 2-in. plastic junction box (Carlon E989NNJ-CAR) I got from Lowe’s for $6.41. Compare that with the $60 that LNR wants for their end-fed antenna.
I put up the antenna about three weeks ago, on a beautiful fall Sunday, running 34 feet of wire up a trellis attached to a small deck in my backyard, then out to a tree near the back of my lot. With more than a little anticipation, I put the antenna analyzer on it, only to be somewhat disappointed with the readings. The SWR was 2.6:1 at 14.000 MHz, dropping to about 1.5:1 at 14.900 MHz.
Since the internal tuner on my IC-746PRO is supposed to be good to 3:1, I did use it and made a couple of contacts. A guy in MA even gave me a 599 signal report. So, while I was a little uncomfortable with an SWR so close to the limit of my tuner, it did seem to radiate pretty well.
I e-mailed the guy who published the design and asked why he thought the resonant frequency was so high, and he said that all I had to do was add a couple feet of wire to the antenna. I also did some more reading about end-feds and several websites suggested that adding a counterpoise might be a good idea, too.
A week later, I finally got back to playing with the antenna. I added 24-in. of wire to it, and it did indeed bring down the SWR of the antenna to below 2:1 in the CW portion of 20m. I’m happier with this. I made a couple of contacts that day, too, with both stations giving me good reports.
I still do plan to try a counterpoise. Not so much to improve the SWR, but to see if it makes the antenna a little more efficient.
Overall, this has been a fun project. I learned something about end-fed, half-wave antennas and saved a bunch of money by rolling my own. Isn't that what ham radio is all about?
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When he's not messing with antennas, Dan, KB6NU publishes the "No-Nonsense" series of amateur radio license study guides. The latest in this series is the No-Nonsense Extra Class License Study Guide. For more information, go to KB6NU.Com or e-mail cwgeek@kb6nu.com
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November 2012