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[Towertalk] C31XR & guy wire detuning

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Subject: [Towertalk] C31XR & guy wire detuning
From: (
Date: Wed, 24 Jul 2002 22:23:15 +0200
Hi Sylvan,

there is a graphic about this in the ARRL antenna book.

The theory is easy: stay away from wire lengths that are even multiples of
lambda/2 for the frequencies you are using. If the wires are grounded,
avoid also multiples of lambda/4.
Using straight numbers for lambda you get the following table of forbidden

10m:  5m, 10m, 15m, ...
15m:  7.5m, 15m, 22.5m, ...
20m: 10m, 20m, 30m,...

It is more important to split the guy wires near the top section of your
tower. The lower you go, the less influence they have.

We often split the first 10-15m of our guy wires into lenghts of 3.5m and
ran the rest at random length (mostly because they were not much longer
anyway...:-) )

73s Con DF4SA

At 13:47 23.07.02 -0600, you wrote:
>Hello All
>I am trying to solve a guy wire problem - they seems to be detuning my
>C31XR. Last year when I installed the antenna I found I could not get the
>swr down to the spec level on 15 and 20. Natan suggested that I my guys
>could be detuning the XR. This summer I inserted insulators right at the top
>of the tower. This brought 15m right on spec! Great!
> I am still having problems on 20m - the minimum swr is about 400 khz too
>high. The bottom sections of each guy is about 54' long. Natan suggests that
>the capacitance caused by the insulators and subsequent following wire
>lengths can easily move the resonance of the 54' to a length near 62 feet
>which is nominally a full wave resonator on 20 meters.
>I want to break the 54' sections into two segments each. My question:
>What should the lengths of these two sections be to minimize their
>interaction with the C31XR?
>.. sylvan
>ps - please do not recommend the use of Phyllistran -- it is too costly to
>have it shipped here :)
>Sylvan Katz, VE5ZX
>Saskatoon, SK
>"A Novel Perspective of Amateur Radio Contesting" at
>Self Supporting Towers, Wireless Weather Stations, see web site: 
>Call 888-333-9041 to place your order, mention you saw this ad and take an 
>additional 5 percent off
>any weather station price.
>Towertalk mailing list

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