I'll try to keep this concise.
My assumption in this is that you want to do as well as possible with
the least loss possible. If instead, you are past dealing with lots of
mechanics and that's why you even dare to mention two elevated
radials, but you don't want to pick up a lot of loss, I suggest you
install FCP's and forget it **. Otherwise, here's radials..
> (A) Is it true that a couple of elevated radials are just as effective as the
> "optimum" amount of buried ones...? If you have to ask this, you've clearly
> never had an optimal buried radial system.
NO. An optimal buried radial system will exceed, significantly better,
or crush two elevated radials, over excellent, average or awful dirt
respectively. Two elevated was a popular scheme a decade or two ago.
Ask W3LPL this question for a brutal refutation of this urban legend.
> (B) What is the "ideal" number of elevated radials that one should use...?
Somewhere between 16 and 32 it gets hard to see any further change.
For commonly achievable 160m heights of radials, the degree of change
depends some on height and more on quality of ground.
> (C) How many elevated radials are "just enough"...?
Depends on how many dB you want to throw away. If you can, do 12 to
16. 32 is the kill-the-loss, never-look-back number.
> (D) How high should these radials be...?
8 feet to get above antlers, hands, etc. Given that you don't want to
garrot a neighbor, or have male deer running through take down your
radials, the height is more of a mechanical, safety issue.
> (E) Would it be a requirement that I raise the feedpoints of my "L's" to the
> same height as the elevated radials, or can I simply leave the bases where
> they are now (at ground level) & simply slant the radials upward with no
> effect upon performance...?
First see the answer to (D), then: Having a base-of-wire feed near
the ground puts a large RF field in the dirt that is a lot of loss and
needs dense radials to counter. Having the base of the wire up at 8
feet, and significantly reducing that field in the ground, is one of
the benefits you throw away by not going up with the feed point.
Moving fields up and away from lossy ground is a plus. Other than
dissipating lightning energy, and giving you something to put tower
bases in, consider ground your lossy enemy that you need to evade.
> (F) Is it OK to bend the elevated radials to fit property allotments...?
Elevated radials need to carry uniform current close in to the feed so
that you get good field cancellation. Each radial in your system needs
to have the same apparent feed impedance to make sure that the current
distributes equally when you hook them together. If you have to fold
them much at all, you may need to shorten ALL of them.
> (G) What is the desirable length of an elevated radial...?
If you have the space for it all the way around, and can get up 12-16,
use the quarter wave. Use an even number of radials, and make sure
that opposite radials fed like a dipole are resonant. This is the
configuration with the least problems, that always plays and offers
few surprises.
If you are constrained in your radials, then figure the longest
possible straight radial in the most confined space and use that
length for all your radials. At the base bring all the radials
together. This will have some amount of capacitive reactance. The
more radials, the less this reactance because the radials are in
parallel. If you need to for matching reasons, put a series inductor
to cancel the reactance between the radial tie-together and the shield
connection from the coax.
Put a 160 meter rated common mode current blocking device on the coax
right at the feed. Get an excellent one, ACTUALLY full rating on 160.
Just do it. Be good to yourself.
> (H) Should any existing connections to real earth at the base of the "L's"
> (i.e. a ground pipe) be completed severed with a system of elevated
> radials...?
Ground the shield of the coax coming down from the feed at the dirt.
This will be on the shack side of the common mode current block. You
do not want the coax to see either earth ground, or the dirt as a
possible counterpoise current path.
> This morning I happened to work a NJ station with elevated radials that
> almost pegged the S-meter on my 751A---the short distance between us
> notwithstanding, obviously something was working very well for him there!
Elevated radials avoid a collection of lossy mistakes that one finds
in less than optimal buried/on ground radials. If a full size radial
system is done properly, dense, uniform all around, you will not be
able to tell the difference. If there were huge efficiency issues
with buried radials never seen with elevated, you would be seeing
elevated radials at AM BC stations all over the place.
24 radials on the ground is not optimal unless you are over midwest
USA flat-land black super-dirt.
73, Guy.
** http://www.w0uce.net/K2AVantennas.html
> Thanks in advance & my vy
>
> ~73!~ de Eddy VE3CUI - VE3XZ
>
>
> _________________
> Topband Reflector
_________________
Topband Reflector
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