On Aug 23, 2007, at 10:25 PM, Dennis McAlpine wrote:
> 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.
How was this study performed? Did they actually build the antennas
and make field strength measurements?
That's what got me with the study that W8JI cited -- the models
suggested the elevated radials should perform just as well, but the
measurements didn't follow the model.
Given that experiment trumps theory, it called into question the
absolute accuracy of the model.
Bottom line: elevated or ground-mounted, the antenna will work.
> 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?
Interesting question. There was a modelling study in the NCJ about a
year or so ago. It indicated that you have to be within about 1
wavelength of the water for there to be any positive effect.
I did read an anecdotal account that suggests there may be more to
this. Fellow used to commute to the mainland across a bridge with an
HF rig in his car. He'd be talking to DX, but then as soon as he'd
get across the bridge, the DX would fade out.
Bill Coleman, AA4LR, PP-ASEL Mail: aa4lr at arrl.net
Quote: "Not within a thousand years will man ever fly!"
-- Wilbur Wright, 1901
|