Tnx, Bill. After reading your comments, I went back to ON4UN's book on LF
operating. He cited a study by A. Chrisman that concluded that four elevated
radials were the equivalent of 120 buried radials if the elevation was at least
15' on 80 meters. He also said that as the underlying ground became poorer,
the height of the elevation had to go higher to have the same effect. Maybe I
ought to go to 15' and forget the 10'. Radio Shack, here we come.
Another question, as I start to search for a suitable remote location, how
close to the ocean do you have to be in order to receive the benefits of salt
water? Obviously, if you can stick the antenna right in the ocean, you have a
good salt water ground and all the benefits that inure. But, how about if your
antenna is 100' from the ocean? or 1/2 mile? or 1 mile? In other words, when
does the distance away from the salt water offset the positive effective of
being on the salt water?
73,
Dennis, K2SX
-----Original Message-----
>From: Bill Coleman <aa4lr at arrl.net>
>Sent: Aug 23, 2007 9:45 PM
>To: K9AY <k9ay at k9ay.com>
>Cc: secc at contesting.com
>Subject: Re: [SECC] Antenna improvements (Was: NAQP)
>
>
>On Aug 23, 2007, at 10:21 AM, K9AY wrote:
>
>> I have not had experience with multiband verticals, but in the past
>> I have
>> used elevated ground planes for 15, 20, 30 and 40 meters -- all of
>> which
>> performed much better than their ground-mounted equivalents.
>
>There was a key study sited by W8JI on TowerTalk several years ago.
>The AMBC guys had actually investigated using a few elevated radials
>rather than a standard ground-mounted radial system. BC stations
>specify 120 1/2 wave radials, which is way better than most amateur
>installations.
>
>The bottom line on the study was that the ground-mounted system gave
>higher field-strength readings than the elevated system. So, they
>stuck with the ground-mounted system.
>
>So, I think it depends on what you are comparing. If you can only put
>down a few radials, then elevating them makes sense. Putting up a lot
>of elevated radials is harder, since you need to support them all.
>(Although W4WA does have that huge spiderweb of 60 1/4 wave radials
>for 160m at 10 feet...)
>
>The other issue is height. Above 1/4 wave high, a few elevated
>radials work great. Below 1/8 wave, its not so clear.
>
>Consider:
>
>Case A: 4 radials below 1/16 wave versus 4 on the ground.
>
>Case B: 4 radials below 1/16 wave versus 30 on the ground.
>
>Case C: 4 radials above 1/16 wave versus 60 on the ground.
>
>I'd say case A is a definite win for elevated radials, but case B
>favors the ground-mounted system. Case C isn't so clear. The exact
>height of the radials would be the determining factor.
>
>Bill Coleman, AA4LR, PP-ASEL Mail: aa4lr at arrl.net
>Quote: "Not within a thousand years will man ever fly!"
> -- Wilbur Wright, 1901
>
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