My tower is near the center of a small lot, 60 by 120 ft (18 by 36 m).
When I decided to shunt feed the tower on 80 and 160 years ago, I
initially put in 13 crooked buried radials, largely based on ON4UN's
book, where he contends that a whole lot of short radials aren't much
better than a small number of them. (Not as good as lots of long
radials, of course, but that's not an option here.) It worked quiet
well. There were 3 ground rods at the base of the tower for lightning
protection. The soil is clay, probably of about average conductivity.
Years later, I buried another 1200 feet of AWG 12 copper wire in a grid
pattern. The impedance of the shunt feed did not change a bit, and the
antenna seems to perform about the same, so I don't think all that wire
did much for its efficiency. However, I think it may significantly
improve the lightning protection. I now have a total of 13 ground rods,
but in this soil their resistance isn't all that low. All that wire has
a lot of surface area, and it's near the surface of the soil. I hope
that's never put to the test, but I figure it can't hurt.
73,
Scott K9MA
On 12/24/2020 4:58 PM, Jeff Blaine wrote:
I guess I'm missing what's the "very bad idea" part of this. We are
talking RF here, not lightning. Right? Antenna in the middle of this
field, right?
If I'm following the explanation, the guy is planning on laying out a
wire that runs from one corner of the plot to another corner, then the
other way, making a big X. The bonding those wires at the center of
that X with a ground rod connecting it all together, and serving as
the antenna ground point. And then later, maybe adding a "+" shaped
overlay of the same.
So he starts out with 4 radials initially, and then 8 later. If he's
coming from 0 radials, then that seems like solid steps in the right
direction.
73/jeff/ac0c
alpha-charlie-zero-charlie
www.ac0c.com
On 12/24/20 4:21 PM, w5jmw@towerfarm.net wrote:
Jim,what about the crossing of the radials.Isn't doing that not
recommended?Right now I can do either.I am confined to such a pattern
due to me antenna placement.I have a overhead power run alomg my east
fence and a metel fence along my west.I have already attached to both
as a ground.really more of a lightning dispersal path.I might point
out that I do have pretty good soil.I have very dense clay in certain
at abt 3-4 foot.It does stop water sippage to a point.Also we have an
aerobic septic system which the spray nozzles are located in thi same
pasture...thank you,john
On 2020-12-24 13:52, Jim Brown wrote:
On 12/24/2020 1:56 AM, w5jmw@towerfarm.net wrote:
What I am wanting to do ie to run radials from corner to
corner.That is to say from ne to sw and from nw to south
east.Initially run these then go from side to side.The radials will
be jouned in the middla by a split bolt to a ground rod....I plan
on using the radial for all the antennas if possible.My
question...First Can I do this ?
The short answer is that this is a very bad idea. The earth is a big
resistor, and if the antenna sees it, it burns a lot of the
transmitter power. Radials or a counterpoise provide a low resistance
return path for the antenna current; radials, in addition, shield the
antenna's field from the lossy earth.
An antenna's field surrounds it on all sides, and for radials to be
effective, they must extend out from the base, and be connected to the
coax shield. An earth connection (ground rod) does NOT make a transmit
antenna work better unless it's to an expanse of salt water.
Radial systems work best if they are symmetrical and dense, but if
available real estate and antenna locations prevent that, the best
layout for on-ground radials is to run as many as you can in as many
directions as you can. There is no need for on-ground radials to be of
equal length. There are many practical ideas about this in a tutorial
talk I've done at ham conventions and club meetings. Slides are here.
No original work by me, but a collection of great work by others.
http://k9yc.com/160MPacificon.pdf
73, Jim K9YC
_______________________________________________
--
Scott K9MA
k9ma@sdellington.us
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