HF-Ground
 

On 20 Jan 2006 02:08:57 GMT, "Bill Turner" wrote:

Owen Duffy wrote:

Bill, I often see the assertion that it is better to not bury radials.

Can you point me to any reputable texts or experimental evidence that
shows the difference between shallow buried radials and radials lying
"on top of the ground"?

Corrosion is often cited as a reason to use insulated buried radials,
but is corrosion a significant risk in most locations. We widely use
buried copper water pipes here, and copper clad earthing electrodes
for the MEN power supply earthing, yet they don't seem to suffer
significant corrosion in most places.

It seems to me that insulated buried radials are likely to be less
effective in a lightning protection role.

Owen
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Your mind is already made up. Do as you like.

I note that you decline to subtantiate the reasons underlying your
advice.

Has anyone references to sound evidence that supports Bill's advice
that radials "Lying on top of the ground is better." than buried.

Owen
--

HF-Ground
 

Owen Duffy wrote:
On 20 Jan 2006 02:08:57 GMT, "Bill Turner" wrote:


Owen Duffy wrote:


Bill, I often see the assertion that it is better to not bury radials.

Can you point me to any reputable texts or experimental evidence that
shows the difference between shallow buried radials and radials lying
"on top of the ground"?

Corrosion is often cited as a reason to use insulated buried radials,
but is corrosion a significant risk in most locations. We widely use
buried copper water pipes here, and copper clad earthing electrodes
for the MEN power supply earthing, yet they don't seem to suffer
significant corrosion in most places.

It seems to me that insulated buried radials are likely to be less
effective in a lightning protection role.

Owen

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Your mind is already made up. Do as you like.


I note that you decline to subtantiate the reasons underlying your
advice.

Has anyone references to sound evidence that supports Bill's advice
that radials "Lying on top of the ground is better." than buried.

Owen
--

Owen;

Given the expertise that Bill has accumulated over the years and the
good advise he has given to anyone who asks I think that your attitude
needs modification. When you were in school did you challenge your
teachers this way? I think not. If you diagreed you kept it to your self
or checked it out on your own.
For what it's worth everything that I have read tends towards placing
the radials on the open ground, usually staked down so as to prevent
tripping or getting caught in a lawn mower.


Dave WD9BDZ

Note to Bill: I know you don't need anyone to defend you but this guy
isn't going to take any answer from anyone. I suggest that we drop him
as a thread. I just know his response is going to be at me demanding
positive confirmation. ;^)..

HF-Ground
 

On Thu, 19 Jan 2006 21:22:25 -0600, "David G. Nagel"
wrote:


Owen;

Given the expertise that Bill has accumulated over the years and the
good advise he has given to anyone who asks I think that your attitude
needs modification. When you were in school did you challenge your
teachers this way? I think not. If you diagreed you kept it to your self
or checked it out on your own.

Dave,

I don't agree, I have never had a teacher worth his salt who responded
to polite questions as Bill did.

No, I don't believe something just because I read it on the 'net, I
would like to know why.

For what it's worth everything that I have read tends towards placing
the radials on the open ground, usually staked down so as to prevent
tripping or getting caught in a lawn mower.

Yes, I see lots of web articles describing that in ham stations, but
it is not the only approach that I see documented and talked about.

In my limited experience, I have not seen commercial HF installations
with radial / ground wires laid above ground in preference to being
buried. The only cases I can recall were because of rock.

Whilst there are articles around about the performance of shallow
buried radials, I have not seen any that deal quantitatively with
radials laid on the ground, or pinned to the ground as you describe,
and the effects of those different installations on antenna
efficiency. That is what I was asking about.

Equally, there a plenty of articles where the author insists that
radials cannot work near the ground and they need to be some distance
above, some stating a quarter wave above.

They can't all have "better" efficiency, the only way to know is to
seek reasons why a configuration is better.

Bill proposed a "better" configuration and declined to explain why /
how it is better.

Owen
--

HF-Ground
 

I used about 1300 ft of insulated copper wire for my 72 radials. I chose to
pin mine to the ground witrh fenc e staples. I did this work in the dead of
winter. I then also covered them with a thin layer of soil. Come spring the
grass grows and the radials are hidden and beneath the applied soil layer so
as to not interfere with the lawn mower.

Pictures of my installation for my Hustler 5BTV at this web page

1. http://www.ad5th.com/5-BTV.html

--

Charlie-AD5TH
www.deepsouthnet.net


"Gary Schafer" wrote in message
...
If you are also going to use the radials for a lightning protection
ground then bare wire is much better.

73
Gary K4FMX


On 19 Jan 2006 06:04:29 -0800, wrote:

Question:

Is you are making a HF-ground (radials just below the surface) Should
these radials be insulated or not?

73 John

HF-Ground
 

David G. Nagel wrote:

Dave WD9BDZ

Note to Bill: I know you don't need anyone to defend you but this guy
isn't going to take any answer from anyone. I suggest that we drop
him as a thread. I just know his response is going to be at me
demanding positive confirmation. ;^)..
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Thanks, Dave. He's history. (I wonder if he'd like positive
confirmation?)

73, Bill W6WRT

HF-Ground
 

On Fri, 20 Jan 2006 04:16:39 GMT, Owen Duffy wrote:

In my limited experience, I have not seen commercial HF installations
with radial / ground wires laid above ground in preference to being
buried. The only cases I can recall were because of rock.

Whilst there are articles around about the performance of shallow
buried radials, I have not seen any that deal quantitatively with
radials laid on the ground, or pinned to the ground as you describe,
and the effects of those different installations on antenna
efficiency. That is what I was asking about.

Equally, there a plenty of articles where the author insists that
radials cannot work near the ground and they need to be some distance
above, some stating a quarter wave above.

Hi Owen,

These three paragraphs reveal arguments that vary by application,
rather than by degree. It seems to me that most AM stations' ground
fields are shallow buried in gravel simply to permit foot traffic. The
HAARP site uses a grid that is elevated sufficiently to allow
vehicular traffic. Neither really attend lightning as they are more
ground screens and principally constructed for RF.

I found a much more compelling report in:
UNITED STATES DEPARTMENT OF AGRICULTURE
Rural Electrification Administration
REA BULLETIN 1751F-802
SUBJECT: Electrical Protection Grounding Fundamentals
Which is vastly more comprehensive and directly answers these
questions when viewed in the terms of the resistivity of the earth
connection.

73's
Richard Clark, KB7QHC

HF-Ground
 

On Thu, 19 Jan 2006 22:19:04 -0800, Richard Clark
wrote:


These three paragraphs reveal arguments that vary by application,
rather than by degree. It seems to me that most AM stations' ground
fields are shallow buried in gravel simply to permit foot traffic. The
HAARP site uses a grid that is elevated sufficiently to allow
vehicular traffic. Neither really attend lightning as they are more
ground screens and principally constructed for RF.

Yes, I understand that a ground system may be called upon to perform a
role as the other terminal of a Marconi for instance, and as the drain
for lightning or other EMP. Hence my earlier comment that a rule of
thumb that buried radials should be insulated seems to deny fullest
lightning protection to mitigate a small risk of corrosion.


I found a much more compelling report in:
UNITED STATES DEPARTMENT OF AGRICULTURE
Rural Electrification Administration
REA BULLETIN 1751F-802
SUBJECT: Electrical Protection Grounding Fundamentals
Which is vastly more comprehensive and directly answers these
questions when viewed in the terms of the resistivity of the earth
connection.

OK, I found it and it is substantial. It will be an interesting read,
thank you for the pointer. It appears to be focused more on power /
lighting protection that an antenna ground system.

For others, the URL is
http://www.usda.gov/rus/telecom/publ...s/1751f802.pdf
..

One of the things that intrigues me is the common "expert" advice to
cut radials for 7MHz to 33' long and bury them. It seems to me that
when buried and considering the wire as a transmission line, the
velocity factor will be somewhere between 0.3 and 0.8 depending on the
soil type, so that 33' is likely to be closer to a half wave
electrically, and present a relatively high and reactive impedance at
the antenna base if it were not for the attenuation of the wave on the
radial. It would seem a length more like 17' to 20' would be a better
estimate by the SWAG method (Scientific Wild Arsed Guess), although if
ground attenuation is high enough, it could be cut shorter and the
extra wire used for another radial for a more effective solution.

More when I digest some of the article.

Thanks again... Owen
--

HF-Ground
 

On Fri, 20 Jan 2006 06:56:42 GMT, Owen Duffy wrote:

One of the things that intrigues me is the common "expert" advice to
cut radials for 7MHz to 33' long and bury them. It seems to me that
when buried and considering the wire as a transmission line, the
velocity factor will be somewhere between 0.3 and 0.8 depending on the
soil type, so that 33' is likely to be closer to a half wave
electrically, and present a relatively high and reactive impedance at
the antenna base if it were not for the attenuation of the wave on the
radial.

Hi Owen,

Calling them "tuned" radials is an artifact of their length being
described in free space wavelength. The proximity of earth negates
such illusions. The association with the necessity of being a quarter
wave long comes by the field data obtained by Brown, Lewis, and
Epstein. This was simply an arbitrary selection born more of the
available wire being portioned out in binary increasing counts
(2,4,8,16....) such that 119 radials depleted their stock (short of
that magic 128). Their work has been offered on the web through the
interests of our discussions here, and by one or several
correspondent's scanning and posting their report. Google this
newsgroup for that link using the authors as a keyword search. This
was offered last summer.

73's
Richard Clark, KB7QHC

HF-Ground
 

Owen Duffy wrote:

Bill, I often see the assertion that it is better to not bury radials.

Can you point me to any reputable texts or experimental evidence that
shows the difference between shallow buried radials and radials lying
"on top of the ground"?

Corrosion is often cited as a reason to use insulated buried radials,
but is corrosion a significant risk in most locations. We widely use
buried copper water pipes here, and copper clad earthing electrodes
for the MEN power supply earthing, yet they don't seem to suffer
significant corrosion in most places.

It seems to me that insulated buried radials are likely to be less
effective in a lightning protection role.

Owen

You're asking some good questions.

Many years ago, I was doing some ground system experiments with a
vertical antenna. I had strung a bunch of radials, consisting of small
insulated hookup wire, on the surface of the ground and I was measuring
antenna input impedance. I was surprised to discover distinct resonance
effects as the radial lengths were changed, something which I hadn't
expected -- they were acting more like elevated than buried radials. It
was summertime and the clay ground was pretty dry.

Then I took some pieces of mild steel wire and "stapled" the wires down
to conform with the ground and bring the wires into close contact with
it. The resonant effects disappeared and the radials acted more like
buried ones. I concluded that even a very small air gap between the
radials and the ground provided some independence from the ground.

More recently I've done some modeling to try and understand the
phenomenon a bit better. I'll give those results in my response to
another of your recent postings.

Oh, as for corrosion -- I'm sure it depends on the soil. But there's no
harm in using insulated wire, as far as RF ground effectiveness goes. I
suppose it would limit the lighning protection voltage to the insulation
voltage, however.

Roy Lewallen, W7EL

HF-Ground
 

Owen Duffy wrote:
. . .
One of the things that intrigues me is the common "expert" advice to
cut radials for 7MHz to 33' long and bury them. It seems to me that
when buried and considering the wire as a transmission line, the
velocity factor will be somewhere between 0.3 and 0.8 depending on the
soil type, so that 33' is likely to be closer to a half wave
electrically, and present a relatively high and reactive impedance at
the antenna base if it were not for the attenuation of the wave on the
radial. It would seem a length more like 17' to 20' would be a better
estimate by the SWAG method (Scientific Wild Arsed Guess), although if
ground attenuation is high enough, it could be cut shorter and the
extra wire used for another radial for a more effective solution.

Modeling clearly shows that using elevated radials which are too long
degrades the efficiency. A quarter wavelength can be determined by
constructing a dipole at the height of the proposed radial system and
adjusting it to resonance. The maximum length of the radials is half the
length of that dipole. If you make them longer, efficiency drops. Very
close to the ground, the length of a quarter wavelength decreases
substantially, so a free-space quarter wavelength can easily be too long.

Modeling presents a very idealized situation, overly so when dealing
with ground. But I believe the general trends and conclusions are
instructive. I modeled a 40 meter vertical over average ground. It had
four 34 foot radials, which were quarter wave resonant when elevated
very high. As I lowered the radials from one foot high to 0.1 inch high,
the gain dropped 4 dB. The main cause of the drop was that the radials
were becoming too long at the low height above ground. Shortening them
to 19.6 feet, the resonant length at that height, increased the field
strength by 2.45 dB. Burying them lowered the field strength to 1.7 dB
below the field strength when 0.1 inch above the ground and of proper
length. There wasn't any substantial change in field strength as the
length was increased beyond about 30 feet, or when the depth was varied
from 0.1 to 6 inches. These changes in field strength are solely due to
changes in efficiency; the pattern shape stays the same.

When modeled at 0.1 inch above the ground, the radial current
distribution is approximately sinusoidal, as in elevated radials. When
buried, even an inch, the current decays in an approximately exponential
fashion away from the center. In the case of the modeled antenna system,
the current was substantially zero beyond about 40 feet.

Conclusions a

1. A small number of radials just above the ground are theoretically a
bit more efficient than the same number of buried radials, providing
that they're not longer than a resonant quarter wavelength at that
height. I say theoretically, though, because I believe it would be
impossible to maintain current balance in the radials at a low height.
So one or two radials would likely hog all the current, resulting in a
less efficient system.

2. Making elevated radials too long, even if the elevation consists of
being just above the ground, can seriously reduce the antenna
efficiency. Buried radials, on the other hand, are insensitive to length
provided they're sufficiently long. This latter fact is well known. I've
found in other modeling I've done that making elevated radials shorter
than a resonant quarter wavelength doesn't negatively impact the
efficiency. So if you have to guess, guess on the short side.

The amount of differences you'll see in real antenna systems will vary
quite a bit depending on ground characteristics, frequency, and number
of radials. And it would be impossible to suspend radials precisely over
a perfectly flat and homogeneous ground as I've done with the models.
But I believe the conclusions are valid.

Roy Lewallen, W7EL