Actually, they can be MUCH shorter than .22 wl, as long as you have enough
of them. Many more shorter is quite a bit better than many fewer longer.
There are free programs by G4FGQ, RADIAL2 is the name I think, but just
google G4FGQ and you will get to his site and free downloads. The radial
program is a good one and answers all the questions being raised. It lets
you manipulate number/length/freq and ground characteristics to show
efficiency. VERY HANDY!
For any given band (40,80,160), if I were in a hurry and wanted the best
efficiency for the time invested, I would put down 16 50' radials as evenly
spaced as possible. Lay them on the ground, secure with lawn staples. Over
reasonably good soil in the first place, you will get > 70% efficiency.
I ran a bunch of measurements on radials starting with 0,2,4, up to about
26. (I laid them out 2 at a time), measuring both 2:1 vswr bandwidth and
feedpoint impedance (at the actual feedpoint, not in the shack). They were
all around 50 to 60' and the band was 80m. I got 90% efficiency at 26, and
had over 70% at 16. Even 8 was not embarassing.
2:1 vswr bandwidth DECREASES with increasing efficiency, as it should.
Feedpoint Z dropped from near 70 ohms to 29 ohms going from 0 to 26 radials
(theoretically perfect for the antenna in question was 26 ohms...an Inverted
L of 42 x 25 ft (height, length). The 70 ohms originally measured with no
radials showed 44 ohms of ground loss (44 + 26 = 70), an efficiency of 37%.
The final value at 26 radials was 26/29 or 89.6% efficiency
I have enough wire laying around to do about 16 more radials of similar
length, (and a nice DX-Engineering ground plate to tie them to), so I should
end up with 52 radials. I would GUESS I might get to 93% or so by adding the
remaining radials.
Again, all insulated #14 THHN wire, laying on the ground, lawn stapled into
place.
The data I got is completely consistent with the ARRL publications that
describe how to get minimum loss for a given wire length available, as well
as with G4FGQ's program. I do think Reg's program is a bit optimistic, but
it points one in the right direction. I have full faith in the studies
published in the ARRL Antenna Handbook on how to optimize a radial field, as
my actual measurements agree very strongly with the article.
Hope this helps ya.
73,
...hasan, N0AN
----- Original Message -----
From: "Bill Coleman" <aa4lr@arrl.net>
To: "Dave Tipton" <dave@lodave.org>
Cc: <towertalk@contesting.com>
Sent: Thursday, June 15, 2006 8:45 PM
Subject: Re: [TowerTalk] re Radials
>
> On Jun 14, 2006, at 9:46 AM, Dave Tipton wrote:
>
>> Where it gets wierd, is that when you bury the radials, you can get
>> away with much shorter runs, primarily because 4 or 5 radials 20
>> feet long, will actually couple to ground nicely if buried. No
>> need for full 1/4 wavelength radials if they're under ground.. It
>> all gets muddled pretty quickly once their an inch under the surface.
>
> I don't think that 4 or 5 20 foot radials are going to be a terribly
> effective groundplane for a 160m vertical.... Even if you bury them.
>
> True, the far ends of the wire do less and less "work" of a ground-
> mounted radial system. If you had 60 1/4 wave radials and 60 1/2 wave
> radials, the 1/2 wavers would be slightly more effective -- but only
> slightly - perhaps a fraction of a dB. So, was it worth using twice
> the wire?
>
> With ground-mounted radials, .22 or .20 wavelength radials will be
> nearly as effective as .25 wavelength, especially if you use 20-30 or
> more.
>
>
>
> Bill Coleman, AA4LR, PP-ASEL Mail: aa4lr@arrl.net
> Quote: "Not within a thousand years will man ever fly!"
> -- Wilbur Wright, 1901
>
> _______________________________________________
>
>
>
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