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Re: [TowerTalk] Delta Loop Info and Opinions?

To: Tom Rauch <w8ji@contesting.com>
Subject: Re: [TowerTalk] Delta Loop Info and Opinions?
From: Joe Giacobello <k2xx@swva.net>
Reply-to: k2xx@swva.net
Date: Thu, 16 Sep 2004 12:26:50 -0400
List-post: <mailto:towertalk@contesting.com>
Tom, thanks for your reply. In all honesty when I read the article, it made sense to me because if one were trying to minimize the interaction between the delta and the tower, minimizing the RF current flow on the tower seemed logical. I went back and rechecked the article to make sure I hadn't gotten it backwards, and I hadn't. I am going to have to reconsider the whole issue in light of your explanation.

BTW, I did mention that the deltas were for 30 and 40M and I had planned on vertically polarizing them and feeding them with balanced line. The reasons for using the loops are that I am looking for some gain and directionality on 30 and 40M with a low takeoff angle, simplicity and I have a lot of experience with quad loops.

I appreciate your input.

73, Joe

Tom Rauch wrote:

* ON4UN in his book recommends detuning the tower by


running a wire


down the side in series with a variable capacitor


and tuning for


minimum current with an RF current probe. However,


it seems that


this would only work for one of the bands, and you'd


have to


accept some interaction with the tower on at least


one of the bands.

I always wonder where some of this stuff comes from.

That's generally the opposite of how you should tune if you
are measuring current. You would generally tune for MAXIMUM
current in the sectionalizing drop wire, NOT minimum. That
insures the sectionalizing area is resonant. Since it is a
"loop", current flowing up equals current flowing down, and
that canels radiation. The end-to-end impedance is highest
at resonance, so the section you tune acts like a
high-impedance parallel tuned network isolating the tower
above and below that area.

The exception to tuning this way is if the area below or
above the tuned area is self-resonant. It also is not the
preferred way to detune a structure, but the preferred way
requires a FS meter.



* Does anyone have any experience with this detuning


trick? Did you


find that it was really necessary?



Well, I've done hundereds of them commercially. I'm not sure how necessary it is in a Ham installation, especially since you never said if the antenna was vertically polarized or what band it was on.



* Do you have any suggestions for how to accomplish


detuning for two


bands? Two wires and two capacitors?



That works, but it interacts if the wires overlap the same area of the structure.



* Does a crankup tower alter this detuning requirement


in any way?

Only if the connections are intermittent.

I have a question, why are you using a delta loop or a loop?
There are good mechanical reasons for using a loop, but
generally electrical reasons are not good. Will this be
vertically polarized?

73 Tom


_______________________________________________


See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA.

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_______________________________________________

See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA.

_______________________________________________
TowerTalk mailing list
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http://lists.contesting.com/mailman/listinfo/towertalk

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