Big Signal on 40m for Limited Space
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The Project ’40m Hex beam’ was not my original idea. When I visited my friend Chuck W7MAP in Texas in September 2005, he showed me some designs of Hex Beams in the internet. I have heard about this antenna but haven’t had a closer look until then. After coming back to Sri Lanka, I started to give a try on a hex beam for 40m since I already have good antennas for other bands.
4S7AB / KA5MAL
Author Nov 2005
Having More than 35 years of experience in the Field of Amateur Radio, I have published many articles in prestigious international publications like, QST, CQ-DL, NCJ, Six-News etc.. Here in this web site, these write-ups are intended to give you knowledge about my designs and projects related to the hobby. The articles about foreign HAM activities are intended to share my experience.
Since I didn’t have a tall tower, I had to use whatever that is available. Therefore I decided to use the 30ft tower for the installation as you can see in the picture above.
It is not possible to buy fiberglass spreaders in Sri Lanka. Therefore I have used sectioned Aluminium tubes of 1/2″ joined by PVC tubes. The centre plate was made using a 1/4″ galvanized iron plate. It is drilled at 60 degree separation for the spreaders to get attached using two 5mm nut/bolt for each spreader. The centre of the plate is drilled and a 3/4″ GI pipe of 6″ is welded.
I had a hy-gain 1:1 commercial balun to be used for the feed point. One can use a homebrew 1:1 balun for feeding. about 10 turns of RG6 cable bundled to prevent RF from leaking through the coax also will work if nothing is available. But a 1:1 balun is recommended.
Rather than giving the dimensions only for the 40m version, I wanted to have the hex beam calculating spread sheet here. Please download and play around. This is a good tool to play around with and understand the different sizes for different bands.
On the air results
After installing the hex beam at 35ft, I was able to work few US stations on 40m using just 100W. This antenna performed about one S unit better than my inverted V and about 2 S units better than 160m vertical loaded on 40m. Definitely this 40m hex beam has a gain but the f/b was worse. When I rotated the antenna, I hardly see a difference. Many hams who have made hex beams gave me different thoughts but I want to add the DL7IO’s analysis of this antenna here. According to his analysis, the height was not enough for this antenna. Minimum height required would be about 60ft . Otherwise the takeoff angle is very high.