[TowerTalk] ground wire thoughts
k9ma at sdellington.us
Thu Dec 24 18:19:25 EST 2020
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.
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
> On 12/24/20 4:21 PM, w5jmw at 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 at 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.
>>> 73, Jim K9YC
k9ma at sdellington.us
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