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Re: [Antennaware] Space between antennas

To: "Jorge Diez - CX6VM" <>,<>
Subject: Re: [Antennaware] Space between antennas
From: "K9AY" <>
Date: Fri, 20 Jul 2007 11:06:02 -0500
List-post: <>
I have also recently heard stories of big interaction problems with the new XM240, worse than the older 40-2CD. The only other commercial antenna I know about is the old KLM 2- and 3-element 40M beams, which have a small effect on 15M, but are quite usable.

Perhaps someone can develop a modification for the Cushcraft beam.

It is not difficult to design a "shorty forty" for low 15M interaction. The distance from boom to loading coils is a key parameter. My homebrew 52-foot element 40M beam has loading coils about 6 foot out from the boom (outer elements are #14 wire inside 20-ft. fiberglass fishing poles). Resonances are near 26 and 48 MHz. I detect no changes on my X9's performance with or without the 40M beam. I might note that these resonances changed very little when the driven element was used alone as a rotatable dipole, and after the refelector was added.

73, Gary

Unfortunately, the Cushcraft 40 will detune the TH7DXX on 15m at any
spacing you can manage on the
same mast.

There have been numerous instances locally of "pulling" any 15 meter
antenna's tuning by co-masted
Cushcraft 40's. It also modifies the pattern at 15m.

This happens because without modification a 40 antenna is also resonant at
three times the
frequency.  Some 40m beams are specifically designed to be placed in
proximity to tribanders, etc.

The Force 12  x40N antennas are linearly loaded, and their secondary
resonance is around 18 MHz
instead of 21. Also their Delta x40 antennas were specifically designed to
eliminate secondary
resonance in 21 MHz band.

There may be other commercial 40m antennas that are non-resonant at 21
MHz, but I don't know of any.

73, Guy.

| Hello, | | I will put a Hy-Gain TH7DXX and a Cushcraft 2 elem. 40 mts Yagi in the | same mast on top of a tower. | | Will apreciate any recomendation about will antenna must be at top and | the space between both antennas for not interaction. | | Thanks in advance | | 73, | Jorge | CX6VM |

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