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

Thu Sep 16 20:49:12 EDT 2004

Tom, thanks again, and it's interesting you brought up the issue of the 
balun on the input of an unbalanced tuner. I have some comments about 
that, but I'm going out of town very early tomorrow (Ivan permitting) 
and will get back to you when I return. BTW, I had some correspondence 
with W7EL on the subject and (I think) I copied you.
Will be back to you later.
73 and thanks for help!
Joe
Tom Rauch wrote:
>>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.
>>>>>>I have something on my webpage at:
>>http://www.w8ji.com/detuning_towers.htm
>>Basically the drop forms a parallel tuned circuit that
>isolates the section. When you measure the cirrect in the
>drop wire, which is what I believe the book suggests, if you
>set the shunt wire current to zero the shunt wire has NO
>effect!!!
>>Going from the top of a structure to ground, or if the tower
>is long in terms of 1/4 wl sections, the results are
>different. In that case the only reliable way to detune is
>to measure the overall effect of the structure on pattern or
>re-radiation with a FS meter.
>>Anyone who has worked with resonant systems knows the
>circulating current is maximum when the system is resonant.
>For example a trap isolating two sections of an antenna has
>maximum current circulating in the trap when the loop
>through the inductor and capacitor forming the trap has
>highest current!
>>Intuitively, as another example, people think moving a balun
>to the input of a floating network makes balance better and
>reduces balun heating. That isn't correct, yet everyone
>believes it. This is why we have to take everything we read
>with a bit of caution, and not go by first instinct.
>>>>>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.
>>>>>>Must have missed that. Loops reduce height requirements, and
>that's a good thing. Just be careful with the feedline. The
>feedline can be more of a worry to decouple than the tower
>supporting the loop.
>>I'd install it first, and worry about problems later if they
>show up.
>>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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