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[Towertalk] Phased Delta Loops

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Subject: [Towertalk] Phased Delta Loops
From: W8JI@contesting.com (Tom Rauch)
Date: Sat, 30 Mar 2002 06:54:27 -0500
> place. I added wire and lowered the freq of each (measured at the end
> of the transformer lines) to 6.085 and flat SWR. When the 2
> transmission lines are connected to a Tee the resonant freq rises to
> the target freq but so does the SWR to 1:7. When the 50 ohm phasing
> line is added the resonant freq drops to 6.900 and the SWr rises to
> 3:1. Would trimming the phasing line in the field raise the target
> freq and lower the SWR ?? Mny Tnx  Mark  K8FU

Hi Mark,

You are going about this absolutely wrong, unless your main goal 
is a certain SWR!

What you are doing is adjusting the elements and phasing to 
obtain a certain impedance in the system and living with phase and 
current distribution errors, and that is totally the opposite of 
traditional goals.

While it may not be what you want to do, most people adjust 
phasing and element lengths or design the system for a certain 
pattern. They then add a matching system that brings impedance 
(SWR) of the **system** to the desired value at the desired 
frequency, without messing with the element lengths or phasing.

You really need to read some of the articles by Roy Lewallen 
(W7EL) or Forrest Gerke (K2BT) about phasing systems and lean 
how to design the system, or find a good proven design and copy 
it. MOSt articles I have read, and even some patents, actually have 
things wrong. It seems phasing is one of the least understood 
things people write about.

Short of doing that, the easiest system to make work would be to 
cut the elements for EXACT resonance with the other element 
removed or totally detuned. Then you feed each element through an 
exactly equal length of coaxial cable to the shack, with the line an 
odd-multiple of 1/4 wl long.

You can then experiment with delay lines of various lengths and 
impedances (or use a "T" network antenna tuner in place of the 
delay line) you find one that gives you high F/B ratio at the desired 
frequency on RECEIVING!!!

Then, after you have the high F/B ratio, you use another tuner to 
match impedances to the radio.

If you start cutting antennas and feedlines to get a certain SWR or 
resonant frequency, actual antenna performance with almost 
always be less than optimum. At times people are happy with 
whatever performance they get by luck, but optimum performance 
only comes from a lot of cut and try (which is why I suggested 
moving the phasing system into the house) or by careful design 
(which is why I suggested articles by Lewallen or Gerke).


73, Tom W8JI
W8JI@contesting.com 

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