Friday, October 31, 2014

HB9CV without capacitor experiment

This post was actually written 2 weeks ago. But things happen so fast here I could not publish it before.

Although I have some experience in building HB9CVs for 11m I didn't manage to build one which completely satisfy me in terms of simplicity, mechanics, bandwidth and SWR. Long time ago I came across a HB9CV design that worked without a capacitor to match the impedance. That means this antenna would be simple and manage unlimited power. I was already planning to rebuild the HB9CV built last year. I made another construction and designed it for 28MHz flat instead of 28,5MHz. In this design the "gammamatch" ,if you can call it like that,  is 2 times longer as the original design, that will say the distance between the boom and were it is mounted on the radiators.

Not trusting designs like this I didn't expect it would properly work but it does actually. SWR at the original design I found was 1:1,4 R=43 X=7. Not bad at all, SWR stays below 1:2 between 27,5 and 28,5 MHz. So I made the elements all 1cm shorter and now the resonance shifted to 28,1 MHz. Since I made the "gammamatch" so it could slide over the radiators I tested if the distance between the mounting point and the boom should be longer or shorter. Till now making it longer giving me a best SWR of 1:1,2 R=45 and X=7. Not bad but of course  I would like to try for 1:1 or at least as close to that as possible, however SWR is not the holy grail. What I was afraid of is how it would affect the radiation pattern. But walking around the antenna with the fieldstrength meter and the whip horizontal shows a max. in the front and a complete nul on the backside. It seems that it doesn't matter were you connect the "gammamatch" as long is you keep the relation in distances.

2 things to do. I'm not satisfied about the connection between the boom and the elements. I have to change it a bit. And making the "gammamatch" wires a little longer to see if I can get a even better match.
This experiment has potential and I hope to get a fine working antenna out of it.

Related links on this blog:

The HB9CV revisited 1
The HB9CV revisited 2
Progress building the HB9CV
HB9CV test

1 comment:

Paul Stam PAØK said...

Hallo Bas, die HB9CV antennes zijn best goed. Jaren gebruikt op 2 meter met goed resultaat. Fijn weekend, 73 Paul