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>From: Tyler Barnett <tbarnett@lexmark.com>
To: <topband@contesting.com>
>Date: 15 Oct 96 21:54:38 EDT
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>I hope that W8JIT and N7CL can comment on this one for me.
>I'd ask this offline, but maybe everyone can benefit from
>the question.
>
>My 80M 4-square is nearing completion (sorry this is an 80M
>question, not a 160M question). I started it last year, and
>laid down 45-50 radials per vertical, but didn't get done
>before winter. Each radial is 50' long, except for about
>20% which can't make it to 50'. I chose this length based
>on articles I read regarding radial fields under shortened
>verticals. I think they said put down at least 40 radials,
>and make them at least as long as the vertical was tall.
>
>I can't put up a tower, so I made up 4 aluminum verticals
>that start at 1.625", and taper to 3/8", and are 45' long.
>I plan to guy them in 2 places, using 25' long copper wire
>"top-hats" on the top set of guys for top-loading to bring
>the verticals into resonance.
>
>On this last vertical I went overboard, and laid down 100
>radials, most of which were 50' long.
>
>Questions:
>
>1 - Do you think 100 radials is overkill for my shortened
> system, or should I add more to the others to match?
>
By my calculations, at 40 radials 50 feet long on 80 meters,
you are at almost exactly 0.03 wavelengths tip to tip
distance. Going to 80 radials might get you a bit over half
a dB of improvement. Going beyond 80 would not produce any
noticeable improvement (unless you have room to lengthen
them). At 50 feet 100 is a bit of overkill but not a lot.
Whatever article you read was giving pretty good advice. If
the half dB is worth the effort to you, go ahead and bring
the other antennas up to 80 radials. If it isn't, the array
might be a little easier to balance if all antennas have the
same amount of ground screen.
>2 - Can I use a noise-bridge or Autek to measure the
> radiation resistance, and add enough extra radials to
> each vertical to "balance" the resistance between all 4
> verticals? Is this even possible to measure?
>
I would be more inclined to make the ground screens similar
and bring each radiator to the same resonant frequency with
the other three disconnected at the feedpoint. Someone with
more experience with the specific array feed method you are
using might have a better method for you to use.
The measurement you describe doing for radiation resistance
is unnecessary if the construction of all the radiators is
the same. For the purpose of designing a matching network
(a shunt inductor is probably optimum for the match), you
can measure one with the others disconnected and the value
should be similar for all of them. Mutual coupling effects
will make measurements difficult when all the elements are
active.
>3 - Are there any suggestions for improvement (considering
> no tower to hang them from, and property restrictions).
>
>Looking forward to competing with all those elevated-radial
>4-squares in the pileups.... :-)
>
>Tyler N4TY
>
You should do quite well against them once you get your
array working.
73, Eric N7CL
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