At 07:35 AM 9/9/2005, Ian White G/GM3SEK wrote:
>At 01:35 PM 9/1/2005, Vojtech Ritzko wrote:
>
> >>I am planning 4SQ for 80M. I have problem with space, due to property
>limitation.
> >>Does anybody compared:
>
>Here are my thoughts so far, but this is my first 4sq so it's all
>theoretical. What I need is some practical input!
>
>The conventional 0.25wl spaced option is easy to feed with 90deg
>phasing, so it would get me on the air quickly. But the radial layout
>would be shortened and non-symmetrical, and that might make it harder to
>obtain good nulls (good rear and side nulls are very important here in
>G-land). Alternatively, I could shorten all the radials to the same
>length of 0.18wl to keep the layout symmetrical... but then the ground
>losses would increase.
Asymmetric radials do NOT imply asymmetric patterns. There's some recent
articles in QEX or QST where extensive modeling was done with all sorts of
radial arrangements.
Asymmetric radials will change the mutual coupling somewhat. You're looking
at "things in the reactive near field".. and everything has an effect
there. If you're using the "current forcing" (1/4 wave lines) approach for
phasing, though, that reduces the impact of mutual Z changes. I'd imagine
though, that the effects of a weird grounding network will be not
particularly bigger than the uncertainties and unevenness of your soil
properties
>The closer-spaced 0.20wl option can be done, but it requires a special
>feed network (eg a Lewallen-Lahlum setup as described recently by
>ON4UN). This non-standard element spacing will require "custom" element
>currents and phasing, which can also be optimized to give almost the
>same performance as a full-sized 4sq with the basic 90deg feed. "We have
>the technology" to do all that (I hope) but it would be a challenge, and
>would obviously take much longer to get on the air.
I don't know that it's all that hard to get the phasing working..
As a starting point, you could just use some relays and work the antennas
in pairs. If what you're really concerned about is the ability to place the
null, as opposed to a dB or so of forward gain, then this might work almost
as well.
Tom, W8JI, recommends a bit of extra phase shift compared to the spacing
(on 1/4 wavelength spaced arrays) which essentially makes them
superdirective. See:http://www.w8ji.com/tx_four_square.htm
>All suggestions welcomed...
>
>
>--
>73 from Ian G/GM3SEK
>_______________________________________________
>
>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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_______________________________________________
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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