Tom,
Thanks for the insightful reply. Looks like there is no free lunch here- I
can't get better performance by simply using a different circle array element.
Bummer, I will have to stick with the verticals.
If space is not an issue, will enlarging the circle diameter make any
difference? Note, however, that I am considering the 3-band commercial
solutions (160, 80, and 40m 8 circles).
Rudy N2WQ
________________________________
From: Tom W8JI <w8ji@w8ji.com>
To: Rudy Bakalov <r_bakalov@yahoo.com>; topband@contesting.com
Sent: Wednesday, February 13, 2013 5:53 AM
Subject: Re: Topband: New 160M high performance receiving antenna at W3LPL
> I have been wondering if the antenna element in phased arrays could be a loop
> rather than a vertical. My thinking is that the loop has some level of
> directivity so phasing two of them should result in better side lobe
> suppression compared to a vertical. Is there any merit to this thought?
> Specifically, will I see better RDF numbers if I were to use loop elements in
> any of the active 8 and 4 circle systems (e.g., DX Engineering, Hi-Z
> Antennas, etc.)?
>
Hi Rudy,
A loop can work in a fixed array, or bi-directional array. My first antenna
allowing me to work JA's through LORAN from Ohio was a long array of loops,
although these were elongated loops. I also had long end-fire arrays of small
inverted delta loops in Cleveland in the 80's, and small active verticals.
Small loops do not work well when used in things like four squares or 8 circle
arrays. A multiple direction array, like a four square or 8-circle, requires a
uniform pattern of uniform phase from each element or cell.
With a small loop, phase flips 180-degrees immediately after crossing the null.
Also, the directivity is generally poor because the small loop has two very
sharp null points though the loop axis, but a broad response everywhere else.
Both of these things actually hurt performance of arrays with loops that depend
on phasing to eliminate side nulls.
Elongated loops are a different story, because (we probably all know) elongated
loops are not really loops in function. They are really phased verticals, and
the horizontal part or component of the conductors is simply a phasing line.
K9AY's, Flags, Pennants, EWE's, and other forms of elongated loops are really
all just phased verticals in function. They have a wider null and no sudden
phase shift at the null, and no null cone at the side or "loop axis".
The best element for a traditional 8-circle or four square will always be a
simple vertical, and even in a broadside array we would want to avoid small
loops with deep axis nulls. They are OK as cells in an end-fire array, but not
particularly advantageous for pattern unless elongated. I used small loops as a
matter of "construction convenience" as deltas in a long endfire array, but the
deep side null in that array was really created by out-of-phase cells of deltas
and not the sharp null pattern of the individual delta. It could have just as
well been verticals with no loss of pattern.
73 Tom
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Topband Reflector
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