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:
>>
>>4SQ with ë/4 spacing, but only ë/8 long radials
>>
>>Versus
>>
>>4SQ with ë/8 spacing with ë/4 long radials
>>
>>TNX
>>
>>OM8AW
Jim Lux replied:
>I'll give you a theoretical take. Others will no doubt give you
>some practical experience.
>
>Closer spacing makes for higher interelement coupling, the
>feedpoint impedances will probably be lower, so the IR losses
>(assuming everything else is identical) will be higher. The resonance
>will be higher Q, and the coupling changes faster with frequency, so
>it will be harder to get good phasing. Some depends on: would you
>use lambda/8 phasing or lambda/4 phasing (or some variant with
>a bit more phase shift than the physical distance (like W8JIs
>scheme), which increases the forward gain a bit).
[...]
>On the other hand, the length of the radials (assuming you're
>planning on putting them on the ground) isn't really frequency
>dependent
[...]
>Lots of wires close to the base is probably more important than
>few wires farther out.
>
>If I had the choice, I'd go for 1/4 wave spacing and short radials.
>Easier tuning and operation, mostly.
...and there the topic ended.
Could I revive it with a slightly different question, please?
I'm planning a 40m 4-square on a lot that isn't quite big enough.
Specifically, there isn't enough space for both 0.25wl element spacing
*and* 0.25wl radials all around. The practical options are either:
0.25wl spacing with radial lengths for two of the elements limited to
0.18wl in some directions; or
0.20wl spacing with 0.25wl radials all around.
Which to choose? Very soon it's going to be decision time.
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.
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.
All suggestions welcomed...
--
73 from Ian G/GM3SEK
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