Thanks Roy for a great yet concise answer to this matter. I misunderstood
about tuned radials. I wish I would have done more then a cursory look at
the matter. Basically all I saw was "tuned radials" and "you can't have too
many". Had I read more I would have eventually seen that buried radials need
not be tuned and that a 1/4 lambda would have been adequate. I have over
1300 ft of radials! Don't ask what my pre-cut "tuned radials" cost me!! I
made sure I had plenty and now that this cabbage is boiled I am glad to see
at least I did not do my station a disservice. Most importantly I learned
something.I am not a new ham but am new to this vertical antenna scene.
I am aware of your reputation in this field Roy and I appreciate your warm,
courteous and most of all informative replies. 73 / DX
--
Charlie
Ham Radio - AD5TH
www.ad5th.com
Live Blues Music
www.492acousticblues.com
"Roy Lewallen" wrote in message
...
Nobody's laughing at you -- it's a topic that's very poorly understood.
Here's how it works with buried radials. . .
It never hurts to make them longer. But beyond some distance, it doesn't
help appreciably -- if the current on a radial has dropped to a negligible
value at its end, extending it won't do anything.
What is this distance? Well, like so many other things, the only really
honest answer is that it depends. As it turns out, the current fades more
rapidly if you have only a few radials. So if you only have a few, it
doesn't help to make them super long. If you have a lot (say, 60 or more),
increasing the length has more effect -- but your system will already be
so efficient that it won't make much difference.
The classic set of measurements of various ground systems was published in
1937 as "Ground Systems as a Factor in Antenna Efficiency" by Brown,
Lewis, and Epstein. Their paper has many graphs of the effectiveness of
various combinations of radial lengths and number of radials for various
vertical heights -- for the particular ground at the place of their
experiments, the characteristics of which weren't recorded. Their data
have been interpreted and reorganized countless times and in countless
ways -- a web search should bring you a lot of hits. But some rules of
thumb (and only rules of thumb) for amateurs(*) emerge:
1. There's not much point in making radials much longer than a free-space
quarter wavelength or so.
2. Increasing the number of radials from 16 to 120 or more will probably
net you less than a couple of dB. That might be worth it to you, it might
not.
These assume more-or-less average soil. If your soil is very dry, you
might benefit from more and/or longer radials.
And of course, there's no point in fussing over exact lengths. There's no
need to even make them the same length. Put down what you can and don't
worry about it. Putting in more won't hurt, nor will making them longer.
But you're not likely to notice much difference between a big installation
and a fairly simple one, unless your ground is extraordinarily poor.
Roy Lewallen, W7EL
(*) An increase in field strength of a few percent is a worthwhile pursuit
for AM broadcasters, because it increases the size of their audience and
hence the value of their advertising. Small increments like that are
completely useless for amateurs, though, so our goals are somewhat
different. Keep that in mind when looking through various analyses and
recommendations, since most are oriented toward broadcasters.
Charlie wrote:
I just want to thank all of you for your kindness and speediness in
pointing out my error as a new vertical antenna user. I am glad several
of you had a laugh on me for burying tuned radials. Thank you for your
kindness and courtesy. Hope to catch each and every one of you on the
bands. I am grateful for the tact and diplomacy that many of you showed
me. True Ham Spirit at it's best.
Based on what I have been told by the gentlemen in this great group I
could have used much shorter radials than any "tuned length". If that is
right then I have achieved a much more effective radial system then what
I would have had I not erred. Is this right? In other words I have more
wire in the ground then I need..right? Now if that is so..does that hurt
or help
TY Roy
73 / DX