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[TowerTalk] XM240

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Subject: [TowerTalk] XM240
From: "Bill Parry" <BPARRY@RGV.RR.COM>
Date: Thu, 14 Jun 2007 11:10:07 -0500
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I am really tired of the Steppir stuff...let's talk about something else.

I have a 2 element Cushcraft XM240. It has been up for about 5 years at
about 40 Meters high and has always been a fine antenna. I have had one
problem with the antenna. I set the point at which I have the lowest SWR at
about 7.075. I knew that the antenna was fairly broad and I wanted to be
sure that the SWR was OK in the CW band. I didn't realize the SWR curve was
not going to be symmetrical and the SWR was going to rise very quickly
toward the bottom of the band. As a result the 2:1 points are about 7.020
and 7.285. The antenna still works nicely in the 7.000 - 7020 range but it
creates problems with my amplifier.

I have always just put up with this, the antenna works well and I am
certainly capable of retuning the amp. A friend was over the other day and
suggested putting a 1/4 wave section of 75 ohm coax inline at the shack to
broadband what the amp sees. I was amazed that I hadn't thought of this
before. I have a full size 80 sloper from the top of the tower and I did
this very thing to it. It works fine and the SWR is good across the entire

So the question is:  Are there any drawbacks to using this procedure on a
yagi? I have lost my notes on the exact frequency that I would chose to cut
the 1/4 for...(yes I know I need to include in the velocity factor.) I
assume that I would choose +/- 7.025. 

It is definitely not worth the time and expense of taking the antenna down
to lengthen the driven element a few inches! 

Any thoughts?

Bill, W5VX


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