[Antennas] Re: [TowerTalk] Delta Loop Info and Opinions?

Thu Sep 16 14:35:36 EDT 2004

Mike, thanks to you and Tom, I now see what's happening here. Defining 
the arrangement as a parallel tuned circuit makes sense.
BTW, I do plan on modeling the antennas before erecting them. I'll let 
you know how I made out.
73 and thanks for your input.
Joe
Michael Tope wrote:
>If you have a NEC program like EZNEC, Joe, you can actually
>model a detuning shunt arm and then look at the current in the
>tower and in the shunt arm. When the properly adjusted the
>current inside the shunt arm/tower loop actually peaks at the
>same time the series current below the shunt arm/tower loop
>connection goes to a minimum. It seems a little counterintitutive
>at first, but makes perfect sense after you think about how a
>parallel resonant circuit works (the section of tower and the
>parallel shunt arm form a big parallel resonant tank circuit)
>that effectively inserts a high RF impedance in series with
>the tower).
>>73 de Mike, W4EF.............
>>----- Original Message -----
>From: "Joe Giacobello" <k2xx at swva.net>
>To: "Tom Rauch" <w8ji at contesting.com>
>Cc: <Towertalk at contesting.com>; <antennas at mailman.qth.net>
>Sent: Thursday, September 16, 2004 9:26 AM
>Subject: Re: [TowerTalk] Delta Loop Info and Opinions?
>>>>>>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.
>>>>>_______________________________________________
>>>TowerTalk mailing list
>>>TowerTalk at contesting.com
>>>http://lists.contesting.com/mailman/listinfo/towertalk
>>>>>>>>>>>>>>>>>>>>_______________________________________________
>>>>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
>>TowerTalk at contesting.com
>>http://lists.contesting.com/mailman/listinfo/towertalk
>>>>>>>>>>_______________________________________________
>>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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>>>>