Antenna ground - how can you tell if it's good
 

Everybody acknowledges that a good ground is required for any amateur
work, especially for a vertical. When I'm putting in an RF ground for
either my station or for an antenna system, how do I know when I've
achieved "good enough"? What works?

Thanks - Mark Sheffield/N0LF

Everybody acknowledges that a good ground is required for any amateur
work, especially for a vertical. When I'm putting in an RF ground for
either my station or for an antenna system, how do I know when I've
achieved "good enough"? What works?

===================================

Anything will work!

To summarise, begining with 1 radial, all you can do is keep laying more
radials until performance ceases to improve. Then that's the best which can
be done at your QTH. Performance can be judged by measuring the strength of
fixed, stable, not too distant, MF and lower frequency HF radio stations in
daylight. There's an effect known as "Reciprocity" which means that an
antenna with its ground system is just as good or bad on transmit as it is
on receive.

If you increase the number of shallow-buried radials by 50 percent and
there's no noticeable improvement then stop laying. Depending on the type of
soil you will end up with a number which, in general, will be fewer than
what you thought of before you started.

With a vertical, much depends on the lowest frequency of interest. Opinions
differ but in my opinion, in average garden soil, there's not much point in
laying shallow buried radials longer than 1/10th of a wavelength. They can
be shorter in very fertile, fine, damp soil and longer in dry sandy or rocky
soil. Fertility is the key. Increase their number according to the above 50
percent guidline.

Layout and bends in the wires are unimportant as are varying lengths. Just
spread them out fairly uniformly over the area available. A 180-degree
missing sector because the house gets in the way is not of great
consequence.

Wire diameter has little electrical effect. Choose wire diameter according
to type of soil and wire durability.

Forget about ground rods. A ground rod is little better electrically than a
horizontal radial of about the same length. A short ground rod can be used
as a common connecting point.

If you like amusing yourself with numbers, and for crude predictions of what
to expect, download programs EARTHRES and RADIALS2 from website below. A
little knowledge of your local soil resistivity can add much to the interest
and help you to forget the lumbago.
---
.................................................. ..........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. ..........

Mark Sheffield, N0LF wrote:
"When I`m putting in an RF ground for either my station or for an
antenna system, how do I know when I`ve achieved "good enough"?"

Measurement accuracy is sometimes overestimated as Reg Edwards, G4FGQ
has often declared in this group. But, you know your RF ground is good
enough when expanding the system brings very little improvement.

You need no RF ground for a properly balanced antenna system. For an
unbalanced antenna, the ground system is 1/2 of the total antenna
system. This system has a total resistance that is the sum of its
desired radiation resistance and its undesired loss resistance. Nearly
all the undesired loss is in the ground system. So, it`s very important
to minimize ground loss in an unbalanced antenna system.

There are two ways to determine that you`ve rid your unbalanced antenna
system of loss resistance. If the loss resistance is zero, the driving
impedance of the 1/4-wave monopole against ground should measure 36.5
ohms (from 1950 Kraus "Antennas" page 315).

The second way is to measure the field intensity along the earth`s
surface at a distance of one mile from the antenna. With 1 watt into the
antenna, the field intensity at one mile is 6.5 millivolts/meter with a
lossless system (from Kraus as above).

Best regards, Richard Harrison, KB5WZI

I should have mentioned. When measuring signal strengths as a measure of
performance there's safety in numbers. Take the average of a fair number of
transmissions, all well above the noise level, at about the same time each
day, using your most stable S-meter with the receiver gain turned down such
that the meter deflection is on the most sensitive sector of its scale.
Allow the receiver to warm up for the same length of time on each occasion
it is used.

S-meter calibration doesn't matter two hoots.

And once set, don't ever touch the receiver gain control.

You should take all these precautions from the time when you have laid only
one radial. You will not wish to dig up already laid radials in order to
re-measure the earlier ones you forgot to treat in the standard manner.

It will be appreciated, to make tests during radial-laying operations by
asking for signal strength reports from your many friends, using THEIR
S-meters, will result in you losing them.

Incidentally, when "I" used this method of testing antenna efficiency I
stopped at 8, 10 feet, radials with a 3 feet rod at the end of each. This
included the domestic incoming main water pipe which made no difference when
THAT was connected. So I stopped.

But my soil resistivity is only about 70 ohm-metres. I can grow anything in
my garden. At present it is covered with a dense growth of 3 feet high
weeds except for a small patch which I use to feed the birds. As if they
didn't get enough to eat anyhow. With the trees and overgrown bushes it is
a wild-life sanctuary for frogs, rats, squirrels and hedgehogs. The only
complaints I get are from the neighbours. But its stopped them complaining
about TVI.
---
Reg, G4FGQ

Thank you very much - these are very helpful ways to approach the
problem.

Best Regards,

Mark Sheffield/n0lf

instead of radials, you COULD just make the grounded side vertical - into a
well, I THINK???
(I'm assuming that would work - but never tried it - my post-hole digger
handles were too short)

"MarkS" wrote in message
om...
Everybody acknowledges that a good ground is required for any amateur
work, especially for a vertical. When I'm putting in an RF ground for
either my station or for an antenna system, how do I know when I've
achieved "good enough"? What works?

Thanks - Mark Sheffield/N0LF


---
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Nice Site,

John-WA4JM

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Hal Rosser wrote:
"Instead of radials, you dould just make the ground side vertical into a
well, I think?"

Not at HF, efficiently, because the ground penetration depth decreases
for an RF wave as frequency increases. It is "skin effect" which
decreases the depth with the square root of the frequency.

A steel well casing may make a good ground return at LF but not at HF.

Best regards, Richard Harrison, KB5WZI

"Richard Harrison" wrote in message
...
Hal Rosser wrote:
"Instead of radials, you dould just make the ground side vertical into a
well, I think?"

Not at HF, efficiently, because the ground penetration depth decreases
for an RF wave as frequency increases. It is "skin effect" which
decreases the depth with the square root of the frequency.

A steel well casing may make a good ground return at LF but not at HF.

Best regards, Richard Harrison, KB5WZI

Keep them earthworms warm at nite.
73
H.
NQ5H

"Bill Turner" wrote
If you have an impedance analyzer you can trust, and if you are using a
1/4 wave vertical (full size, not loaded), and if your ground is
perfect, you should measure about 36 ohms at the feedpoint. Any
measurement higher than that is due to ground loss.
_________

But in practical terms, how do you get a "perfect" earth ground reference
for the analyzer to use when making the measurement?

RF