Radial Length
Russ
the lengths of the radials? Is 16'6" ok or do they need to be tuned
like the radiator whip.
Russ
Steve
If you verticals are elevated then the radials need to be tuned (trimmed
fairly accurately), if they are ground mounted then leave them longer.
If you have an antenna analyser (or a mate with one) it is worth spending
the time experimenting - I have one and it saved me hours !!
Steve G4KIV / ZC4BS
homepage: http://www.stevebb.com
Email: yzf100...@yahoo.com
funkbastler
wrote:
>Hi Russ,
>
>If you verticals are elevated then the radials need to be tuned (trimmed
>fairly accurately), if they are ground mounted then leave them longer.
>
Devil's advocate here.....
What difference does it make if it's elevated or not?
Vertical antenna is unbalanced... if the radiator is
resonant, what difference does the radial length make
(elevated or not), as long as they're longer than 1/4
wavelength?
Put another way, if I stick a 1/4 wave vertical element
in the middle of a metal disk that's larger than 1/4 wave
in radius, is it going to work better sitting on the ground
than sitting multiple wavelengths up in the air?
-fb-
W5DXP
> What difference does it make if it's elevated or not?
Ground mounted radials are detuned by the ground. If they
are elevated to 1/2WL, the detuning is greatly reduced.
--
73, Cecil http://www.qsl.net/w5dxp
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Richard Clark
<funkb...@yahoo.com> wrote:
>Devil's advocate here.....
>
>What difference does it make if it's elevated or not?
>
>Vertical antenna is unbalanced... if the radiator is
>resonant, what difference does the radial length make
>(elevated or not), as long as they're longer than 1/4
>wavelength?
>
>Put another way, if I stick a 1/4 wave vertical element
>in the middle of a metal disk that's larger than 1/4 wave
>in radius, is it going to work better sitting on the ground
>than sitting multiple wavelengths up in the air?
>
>-fb-
Better is a state of mind. Better for match? Better for radiation?
Better for cost? Better for materials?
Any radiator that is close to a loading influence becomes broad banded
through the lowered Q. Loss makes critical tuning less critical.
Height, on the third hand, brings the geometry of launch angles into
the game - some heights are better than others for a particular
purpose (not all heights are best for all purposes).
If you had a perfectly conducting disk of even up to 1 wavelength at
ground level, it may still suffer in comparison to the simple ground
plane located higher up (if we are talking DX in the HF). If you can
hike the ground plane that high, you may find that a dipole could have
done just as well.
Better is a cost/benefit analysis across many variables. Frequently
the effort does not justify the benefit, even if the paper answer says
better.
73's
Richard Clark, KB7QHC
Dick Carroll;
Russ wrote:
Russ you evidently missed this thread from a few days ago. Her is the meat
of it repated.....
Dick
Subject:
Re: What length counterpoise?
Date:
Wed, 11 Jun 2003 21:32:12 -0400
From:
"Peter Brackett" <ab...@ix.netcom.com>
Organization:
MindSpring Enterprises
Newsgroups:
rec.radio.amateur.antenna
References:
1 , 2 , 3 , 4 , 5 , 6
Folks:
I have used tuned counterpoises with the antenna system I was discussing
in
two different QTH's both were in deed restricted neighbourhoods where
antennas were forbidden. The antenna was an inverted L antenna made from
quite fine and flexible Radio Shack SWL antenna wire with shirt button
style
insulators, in both cases it was strung up the side of a big southern
yellow
pine tree and then across to another such tree. About 2/3 of the antenna
was vertical, and about 2-3 inches from the trunk of the 1-1/2 foot
diameter
pine tree trunk, the remaining 1/3 was horizontal at about 35 - 40 feet.
Dimensions were never known exactly and the antenna was erected at dusk
using a sling shot and lead fishing weights so the neighbours would not
notice. At first I fed this stealth inverted L antenna against a single 8
foot copper ground rod, and I got lousy signal reports. Only some hams a
few miles away could hear me.
Then I decided to try to improve things by "messing" with my ground
system,
that's when I discovered that "tuning"counterpoises was a great thing.
Just to be clear, I didn't "bury" the counterpoises rather they were laid
out on the ground/grass
and only pressed into the grass far enough so as not to engage the blade
of
my lawn mower.
They were not "radials" they were individual counterpoises, i.e. they were
not all of equal length spread out at equal angles as for a single band
monopole or MF broadcast antenna, rather they were "one of" counterpoises,
one per band and each was of a different length, the longest for 160m, the
next shorter for 80m, the next for 40m, etc... and were used together as
the counterpoise to an inverted L antenna which was operated against those
counterpoises as an all-band antenna fed by a "tuner".
Each counterpoise was "tuned" to length by adjusting for maximum current
in
the countepoise for that band.
Previously that inverted L "stealth" antenna had been worked against a
single 8 foot ground rod, and it didn't work
worth a damm.
With the "tuned" counterpoises the antenna was a real winner and I worked
over 100 countries and countless CW net and traffic QSO's using that
antenna
with it's tuned counterpoises.
Worked for me.
FWIW...
--
Peter K1PO
Indialantic By-the-Sea, FL.
"Roy Lewallen" <w7...@eznec.com> wrote in message
news:veeu0cc...@corp.supernews.com...
> Reg is right that when radials are buried, moderate length changes make
> very little difference.
>
> But I discovered something interesting many years ago. When I laid
> radial wires on the ground, I found very definite and surprisingly large
> sensitivity to their length. Relatively small changes in length
> noticeably changed the antenna input impedance, as if the radials were
> elevated. The ground surface was a bit lumpy, and the soil very dry.
> (Yes, the ground does dry out here for a couple of months in the
> summer.) And the wire wasn't particularly straight, so there were a lot
> of air gaps under the wires. Out of curiosity, I made up some "staples"
> out of short pieces of galvanized steel electric fence wire, and
> "stapled" the wires firmly down to conform with the ground surface. Lo
> and behold, the length sensitivity just about disappeared.
>
> So I don't doubt that Peter has seen the effects he mentions. But I also
> believe that the effort is a waste of time if the radials are to be
> buried after the exercise.
>
> Roy Lewallen, W7EL
>
> Reg Edwards wrote:
> >>Peter Brackett wrote:
> >>
> >>>Then go out in the lawn/garden with wire cutters and cut some of the
> >
> > end
> >
> >>>off the radial, then go
> >>>back and look at the meter. Repeat the process until you find the
> >
> > maximum
Dick Carroll;
Russ wrote:
Russ you evidently missed this thread from a few days ago. Here is the
meat of it repeated.....
Steve
>What difference does it make if it's elevated or not?
Hi Funk,
If the vertical is elevated the radials MUST be tuned or else you will not
get a correct match - very easy to check the imbalance with an MFJ 259
meter. It also helps if you have several books confirming the same details
lol
I tried it with my own Hustler 5BTV antenna and once I made the radials
resonant and elevated the antenna it works a treat.
Try some searching on the internet for a better explanation - I'm only
giving the punchline which is:
Elevated antenna = tuned radials
Ground mounted = untuned (but as long as possible).
Steve