Topband: New 160M high performance receiving antenna at W3LPL
zuceman at yahoo.com
Thu Feb 14 08:25:26 EST 2013
8 Circle Receiving Arrays..
Appears to me that the general consensus is that for maximum single band performance - the best way to build a receiving BSEF 8 circle is with resonant (passive) vertical elements. The circle diameter is probably best (for single band 160M) about 351 foot diameter (.327 wave radius).
My question for this astute reflector is whether there is any reason multiple receivers can't be connected to the array - listening in the same or different directions. Simply by multiple layers of the same RF switch matrix with proper selection/phasing etc. Would a magic T be required from each element into the separate switch matrices?
Frank or Tom - are you already doing this?
--- On Wed, 2/13/13, Tom W8JI <w8ji at w8ji.com> wrote:
From: Tom W8JI <w8ji at w8ji.com>
Subject: Re: Topband: New 160M high performance receiving antenna at W3LPL
To: "Rudy Bakalov" <r_bakalov at yahoo.com>, topband at contesting.com
Date: Wednesday, February 13, 2013, 5:53 AM
> 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.)?
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.
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