[Top] [All Lists]

Re: [TowerTalk] Beta match adds capacitive reactance on 2 el Hy-gain 40m

Subject: Re: [TowerTalk] Beta match adds capacitive reactance on 2 el Hy-gain 40m (reply)
From: David Gilbert <>
Date: Mon, 29 Oct 2012 11:36:32 -0700
List-post: <">>

My Optibeam OB2-40 two element coil loaded shorty 40 uses the exact same thing for a match ... a small coil at the feedpoint wound with aluminum tubing ... and as you say, it works great. I had measured the dimensions of that coil before I installed it, so I was able to reasonably estimate its inductance. When I modeled the antenna with EZNEC+ using the element dimensions from the OB2-40 manual, the inductance of the "hairpin coil" required for a match turned out to be almost exactly that which I had estimated from the measured dimensions.

I suspect, therefore, that in many situations the required inductance can be calculated with enough dependability that the ability to adjust a true hairpin probably is not needed ... and in my opinion the coil is a simpler solution.

Dave   AB7E

On 10/28/2012 7:26 PM, Scott Yost wrote:

Two years ago I built a 2 element 40 meter yagi.  I tried to use a DXE
hairpin, but could not effect a match.  After consulting with DXE tech
staff I abandoned it, as the device they sell did not offer adequate
matching range.   I broke out my 1974 ARRL Antenna Handbook and used its
charts to determine the reactance needed for the impedance transformation
and wound an inductor to place across the feedpoint.  It worked like a
charm.  I used aluminum clothesline wire to avoid dissimilar metal issues
at the contact with the driven element, and sealed all connections well.
Beyond the ARRL Antenna Handbook, the other key was my VA-1 antenna
analyzer, which was very instructive.  And the magnifying lamp on the work
bench.  Those charts were really small.   73 & GL, NM8R

TowerTalk mailing list


TowerTalk mailing list

<Prev in Thread] Current Thread [Next in Thread>