In a ground plane, what dictates the number and spacing of radials?
 

I have seen some with 4 elements, some with 5. Also is the spacing
between them important?

On 10 Jan 2005 08:48:37 -0800, wrote:

I have seen some with 4 elements, some with 5. Also is the spacing
between them important?

The ¼-wave groundplane was developed by George Brown 1938. Here's a
partial quote from his book:

"... In our initial experiments we found that only two horizontal rods
(ground rods) functioned as well as four. Many people from the
Broadcast Sales organization came by to view our tests and they always
expressed doubts as to the ability to radiate uniformly when only two
ground rods were used. To quiet them, we used four ground rods for a
while, thus stilling the criticism. When the antenna became really
popular, we did not dare confess to our ruse."

There you have it from the inventor of the antenna.

73
Danny, K6MHE

"Dan Richardson" wrote in message
...
On 10 Jan 2005 08:48:37 -0800, wrote:

I have seen some with 4 elements, some with 5. Also is the spacing
between them important?

The ¼-wave groundplane was developed by George Brown 1938. Here's a
partial quote from his book:

[deleted]

Interesting... although while I'd certainly believe that, as far as Georbe
Brown could tell in 1938 two radials performed just as well as four radials,
I'd imagine that there is a measurable and simulatable different between the
two systems!

(Hmm... I know... how about... three! ground radials? :-) )

---Joel

In message .com,
writes
I have seen some with 4 elements, some with 5. Also is the spacing
between them important?

A ground plane is an attempt to simulate the earth, with better
conduction, so the more radials the better.

Mike
--
M.J.Powell

M. J. Powell wrote:
In message .com,
writes
I have seen some with 4 elements, some with 5. Also is the spacing
between them important?

A ground plane is an attempt to simulate the earth, with better
conduction, so the more radials the better.

Mike
--
M.J.Powell


Is that a joke?

On another note, why are some of the radials bent to a 45 degree angle
and some are not?

wrote in message
oups.com...
Is that a joke?

No, in most implementations, ground radials are very much attempting to
simulate a solid, perfectly conducting plane under the antenna. Given
enough of them, they do a reasonably good job.

On another note, why are some of the radials bent to a 45 degree angle
and some are not?

As you go to few and fewer radials, the 'pull' of the 'simulated' ground
becomes 'weaker' in a sense and the radiation pattern of an antenna with
horizontal radials tends to have its maximum at an angle significantly above
the horizontal plane. By angling the radials downward, the radiation
pattern is pulled back downward and the maximum radiation is again more or
less horizontal.

(If you don't like this 'maybe intuitive to me and not at all to you'
explanation, you can simulate an antenna with radials in, e.g., ezNEC and
see what the actual results are...)

---Joel Kolstad

Interesting... although while I'd certainly believe that, as far as
Georbe Brown could tell in 1938 two radials performed just as well as
four radials, I'd imagine that there is a measurable and simulatable
different between the two systems!

(Hmm... I know... how about... three! ground radials? :-) )


Actually, for decades, I have built and used 3 radial ground plane
antennas for 2M and for 440. I simply used brass welding rods and SO-
239 connectors to construct them. The reason I used 3 radials.... I too
was under the misconception that 4 were best, but I had a slight
difficulty adding the 4th radials to my SO-239s so I stuck with three.
Incidently, I found the best 50 ohm match was made when I bent the
radials down about 45 degrees. They worked extremely well when properly
tuned and stood up to some pretty heavy weather, too.



Ed

Assuming the terminal resistance of a resonant dipole is 72 ohms,
then a ground plane separating the halves of the dipole means the
terminal resistance of each half is 36 ohms. Thus the terminal
resistance of the half-dipole over the ground plane is also 36 ohms.
The terminal resistance of the half dipole operating against the
radials bent down can then be any value between 36 and 72 ohms,
depending on the angle of the bending. If the bending changes the
angle from 90° to 180° the resistance has changed from 36 to 72 ohms.
The terminal resistance will be 50 ohms at some angle in between, and
is usually close to 45°.

Hope this helps in understanding what occurs from bending the radials
downward.

Walt, W2DU

Sorry, fellas, I intended to mention in my previous post that I worked
with Dr. George H. Brown in his antenna lab at the RCA Laboratories in
Princeton, and he took great delight in telling me about the 'ruse'
that Dan, K6MHE,related concerning the ground plane with only two
radials. 'Ya got that right, Dan Boy!

Walt, W2DU

Walter Maxwell wrote:

The terminal resistance will be 50 ohms at some angle in between, and
is usually close to 45°.

Not to mention that's a damn handy angle when you need the
radials to double as guy wires... ;)

The terminal resistance will be 50 ohms at some angle in between, and
is usually close to 45°.


Not to mention that's a damn handy angle when you need the
radials to double as guy wires... ;)


Not to mention further, it helps keep birds off!!



Ed

You only need two to result in field cancellation
to prevent radiation. However, that is only the
case in free space. Any near objects or objects
in electrical contact may distort
the field from one of the elements differently
from the other, so resulting in less-than-perfect
cancellation, especially in the case of ground radials.

"Dan Richardson" wrote in message
...
On 10 Jan 2005 08:48:37 -0800, wrote:
I have seen some with 4 elements, some with 5. Also is the spacing
between them important?
The ¼-wave groundplane was developed by George Brown 1938. Here's a
partial quote from his book:
"... In our initial experiments we found that only two horizontal rods
(ground rods) functioned as well as four. Many people from the
Broadcast Sales organization came by to view our tests and they always
expressed doubts as to the ability to radiate uniformly when only two
ground rods were used. To quiet them, we used four ground rods for a
while, thus stilling the criticism. When the antenna became really
popular, we did not dare confess to our ruse."
There you have it from the inventor of the antenna.

Such an excellent and succint didactic exposition deserves
wider recognition.....

"Walter Maxwell" wrote in message
...
Assuming the terminal resistance of a resonant dipole is 72 ohms,
then a ground plane separating the halves of the dipole means the
terminal resistance of each half is 36 ohms. Thus the terminal
resistance of the half-dipole over the ground plane is also 36 ohms.
The terminal resistance of the half dipole operating against the
radials bent down can then be any value between 36 and 72 ohms,
depending on the angle of the bending. If the bending changes the
angle from 90° to 180° the resistance has changed from 36 to 72 ohms.
The terminal resistance will be 50 ohms at some angle in between, and
is usually close to 45°.
Hope this helps in understanding what occurs from bending the radials
downward.
Walt, W2DU

PS. The same effect occurs in the so-called "capacity hat".
The waves rushing out and returning in both directions result
in field cancellation and no radiation from the hat in the
ideal case. "Capacity Hat"? - Because the delayed returning
waves in recombination at the top of the radiator behave
as though they have picked up a capacitive phase change.

"Airy R.Bean" wrote in message
...
You only need two to result in field cancellation
to prevent radiation. However, that is only the
case in free space. Any near objects or objects
in electrical contact may distort
the field from one of the elements differently
from the other, so resulting in less-than-perfect
cancellation, especially in the case of ground radials.

"Dan Richardson" wrote in message
...
On 10 Jan 2005 08:48:37 -0800, wrote:
I have seen some with 4 elements, some with 5. Also is the spacing
between them important?
The ¼-wave groundplane was developed by George Brown 1938. Here's a
partial quote from his book:
"... In our initial experiments we found that only two horizontal rods
(ground rods) functioned as well as four. Many people from the
Broadcast Sales organization came by to view our tests and they always
expressed doubts as to the ability to radiate uniformly when only two
ground rods were used. To quiet them, we used four ground rods for a
while, thus stilling the criticism. When the antenna became really
popular, we did not dare confess to our ruse."
There you have it from the inventor of the antenna.

On Tue, 11 Jan 2005 08:50:27 -0000, "Airy R.Bean"
wrote:

Such an excellent and succint didactic exposition deserves
wider recognition.....

Whilst an interesting contribution, for which thanks are due to the
OP, many of us knew this already. Didn't you, Bean? If you already
knew this, why have you not explained it before? Can't you write in
excellent, succinct, and/or didactic fashion? Or have you just gone up
the learning curve?

"Walter Maxwell" wrote in message
.. .
Assuming the terminal resistance of a resonant dipole is 72 ohms,
then a ground plane separating the halves of the dipole means the
terminal resistance of each half is 36 ohms. Thus the terminal
resistance of the half-dipole over the ground plane is also 36 ohms.
The terminal resistance of the half dipole operating against the
radials bent down can then be any value between 36 and 72 ohms,
depending on the angle of the bending. If the bending changes the
angle from 90° to 180° the resistance has changed from 36 to 72 ohms.
The terminal resistance will be 50 ohms at some angle in between, and
is usually close to 45°.
Hope this helps in understanding what occurs from bending the radials
downward.
Walt, W2DU


--
from
Aero Spike

Ok, I think I am learning something here. If radials simulate earth,
would using a solid steel plate instead of radials be better?

wrote:
Ok, I think I am learning something here. If radials simulate earth,
would using a solid steel plate instead of radials be better?

OK till it rusted away. Some very fine antennas have used
metal roofs for their ground planes.
--
73, Cecil http://www.qsl.net/w5dxp


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wrote:
Ok, I think I am learning something here. If radials simulate earth,
would using a solid steel plate instead of radials be better?

Depends on how you define "better".

For an elevated antenna, once you get beyond about 3 or 4 radials, the
increamental difference in performance for added radials is such that
you would never notice it in a practical application.

A solid plane has the disadvantages of being heavy, has a much larger
wind loading, and is difficult to "droop" to get closer to 50 Ohms.

You can download the demo version of EZNEC from http://www.eznec.com/
and model a simple vertical with varying numbers of radials and see
for yourself.

--
Jim Pennino

Remove -spam-sux to reply.

On Tue, 11 Jan 2005 09:41:57 +0000, Spike
wrote:
many of us knew this already. Didn't you, Bean? If you already
knew this, why have you not explained it before?

Hi OM,

Much the same faint complaint could be lain against you, which is to
say, seeing as you "knew this" why didn't you explain it as well?

This is simply stealing Walt's thunder. It takes only once, and that
moment passed.

73's
Richard Clark, KB7QHC

On Tue, 11 Jan 2005 08:35:36 -0800, Richard Clark
wrote:

On Tue, 11 Jan 2005 09:41:57 +0000, Spike
wrote:
many of us knew this already. Didn't you, Bean? If you already
knew this, why have you not explained it before?

Hi OM,

Much the same faint complaint could be lain against you, which is to
say, seeing as you "knew this" why didn't you explain it as well?


Simple. The context for the information posted is that Bean held a VHF
licence for many years before getting the HF licence. In my own case,
I have never been interested in VHF, confining myself to HF and
ground-mounted verticals, where the option of sloping any radials is
not available. I also believe that Walt's information has been
published in roughly similar form many years ago, although I don't
have the reference to hand.

Further, my original post on this also said "...an interesting
contribution, for which thanks are due to the OP...", which you
snipped.
--
from
Aero Spike

"Airy R.Bean" wrote in message
...
Such an excellent and succint didactic exposition deserves
wider recognition.....

The man (Mr. Walter Maxwell) writes excellent books too! :-)

wrote in message
...
wrote:
Ok, I think I am learning something here. If radials simulate earth,
would using a solid steel plate instead of radials be better?

Depends on how you define "better".

For an elevated antenna, once you get beyond about 3 or 4 radials, the
increamental difference in performance for added radials is such that
you would never notice it in a practical application.

Doesn't it somewhat depend on frequency? I.e., how electrically large those
radials appear to the antenna?

I ask due to having seen how commercial AM radio station antennas are
built -- usually something pushing a dozen radials, often over a wire mesh
as well.

I'm thinking that in the case of a commercial station, they often multiple
phased antennas to try to precisely control their radiation pattern, in
which case have each antenna be 'as ideal as possible' probably helps.

---Joel

On Tue, 11 Jan 2005 17:14:58 +0000, Spike
wrote:
I also believe that Walt's information has been
published in roughly similar form many years ago, although I don't
have the reference to hand.

Hi OM,

There's a good chance it was from one of Walt's own many publications,
or it was, as he said, Dr. George H. Brown (the nominal, ultimate
source) with whom he worked.

73's
Richard Clark, KB7QHC

Joel Kolstad wrote:
wrote in message
...
wrote:
Ok, I think I am learning something here. If radials simulate earth,
would using a solid steel plate instead of radials be better?

Depends on how you define "better".

For an elevated antenna, once you get beyond about 3 or 4 radials, the
increamental difference in performance for added radials is such that
you would never notice it in a practical application.

Doesn't it somewhat depend on frequency? I.e., how electrically large those
radials appear to the antenna?

I ask due to having seen how commercial AM radio station antennas are
built -- usually something pushing a dozen radials, often over a wire mesh
as well.

I'm thinking that in the case of a commercial station, they often multiple
phased antennas to try to precisely control their radiation pattern, in
which case have each antenna be 'as ideal as possible' probably helps.

---Joel

Notice the words "For an elevated antenna" which presumes you are working
at a frequency where there is no problem with 1/4 wave radials.

For low frequencies, as in AM broadcast and the lower HAM bands, elevated
antennas become impractical and must be ground mounted, which means the
radials are usually buried as well as there may not be enough room
for 1/4 wave radials.

For radials on or in the ground, usually 4 to 8 1/4 wave radials is
good enough.

If space is limited so 1/4 wave radials aren't possible, the number
required goes up.

The ARRL Antenna Handbook has a good discussion on this.

You might also look at http://www.cebik.com/radio.html which has a couple
of articles about radials, buried and otherwise.

--
Jim Pennino

Remove -spam-sux to reply.

wrote:

In a ground plane, what dictates the number and spacing of
radials?

The height of the antenna above ground in wavelengths. Yes, at a 1/2
wave
or more up, even just two radials are pretty decent. But at 1/8 wave or

lower, 2 radials are just barely above the "waste of time" level as far
as
reducing ground losses... Take two ground planes. Both are at 20 ft at
the base. Each has two radials. But one is for 145 mhz, and the other
is
for 1.85 mhz. Do they have equal ground losses? Not hardly... MK

On Tue, 11 Jan 2005 09:50:30 -0800, Richard Clark
wrote:

On Tue, 11 Jan 2005 17:14:58 +0000, Spike
wrote:
I also believe that Walt's information has been
published in roughly similar form many years ago, although I don't
have the reference to hand.

Hi OM,

There's a good chance it was from one of Walt's own many publications,
or it was, as he said, Dr. George H. Brown (the nominal, ultimate
source) with whom he worked.

73's
Richard Clark, KB7QHC

My 1978 Antenna Handbook by Orr & Cowen, page 92, references drooping
radials at a 45 degree angle for a better impedance match, raising the
gain of the ground plane antenna by about 0.5 decibel over the normal
configuration.

'Course Walt probably preceeded those guys :-)

bob
k5qwg

"Bob Miller" wrote in message
...
On Tue, 11 Jan 2005 09:50:30 -0800, Richard Clark
wrote:

On Tue, 11 Jan 2005 17:14:58 +0000, Spike
wrote:
I also believe that Walt's information has been
published in roughly similar form many years ago, although I don't
have the reference to hand.

Hi OM,

There's a good chance it was from one of Walt's own many publications,
or it was, as he said, Dr. George H. Brown (the nominal, ultimate
source) with whom he worked.

73's
Richard Clark, KB7QHC

My 1978 Antenna Handbook by Orr & Cowen, page 92, references drooping
radials at a 45 degree angle for a better impedance match, raising the
gain of the ground plane antenna by about 0.5 decibel over the normal
configuration.

'Course Walt probably preceeded those guys :-)

I thnk it predates 1978 by some margin. I may even be in one of the old
"Admiralty Handbooks", if anyone has a copy to hand they could check.

The explanation is a fairly standard one, although Walt does express it
well. If Walt is the originator of the idea I suspect he has a many more
turns on the coil than he is admitting ;-)


--
Brian Reay
www.g8osn.org.uk
www.amateurradiotraining.org.uk
FP#898

On Tue, 11 Jan 2005 09:50:30 -0800, Richard Clark
wrote:

On Tue, 11 Jan 2005 17:14:58 +0000, Spike
wrote:
I also believe that Walt's information has been
published in roughly similar form many years ago, although I don't
have the reference to hand.

Hi OM,

There's a good chance it was from one of Walt's own many publications,
or it was, as he said, Dr. George H. Brown (the nominal, ultimate
source) with whom he worked.

73's
Richard Clark, KB7QHC

The reference I had in mind was an article or item in the RSGB's
flagship journal (Radio Communication at that time?) which had a
picture of the two-radial vertical and a description of what happened
when the radials were progressively angled below the horizontal. This
must have been 15+ years ago. I can't recall now if it referenced any
of the said gentlemen's works, but the parallels are there.
--
from
Aero Spike

"Spike" wrote in message
...
On Tue, 11 Jan 2005 09:50:30 -0800, Richard Clark
wrote:

On Tue, 11 Jan 2005 17:14:58 +0000, Spike
wrote:
I also believe that Walt's information has been
published in roughly similar form many years ago, although I don't
have the reference to hand.

Hi OM,

There's a good chance it was from one of Walt's own many publications,
or it was, as he said, Dr. George H. Brown (the nominal, ultimate
source) with whom he worked.

73's
Richard Clark, KB7QHC

The reference I had in mind was an article or item in the RSGB's
flagship journal (Radio Communication at that time?) which had a
picture of the two-radial vertical and a description of what happened
when the radials were progressively angled below the horizontal. This
must have been 15+ years ago. I can't recall now if it referenced any
of the said gentlemen's works, but the parallels are there.

I'm sure it is much older than 15 years- it was around when I did my RAE
(more than 15 years !). I'm pretty sure it is the the old Admiralty
Handbook, but I can't lay my hands on mine. You see a similar effect when
making a dipole into and inverted V.

It is certainly taught on at least one Advance RCE course ;-)

--
Brian Reay
www.g8osn.org.uk
www.amateurradiotraining.org.uk
FP#898

Brian Reay wrote:
The explanation is a fairly standard one, although Walt does express it
well. If Walt is the originator of the idea I suspect he has a many more
turns on the coil than he is admitting ;-)

From "Radio Handbook" by Bill Orr, 20th edition, copyright 1975,
section/page 27.9: "The feedpoint impedance of a ground plane may
be raised to about 50 ohms by drooping the radials down at a 45
degree angle." Anyone got an earlier edition?
--
73, Cecil http://www.qsl.net/w5dxp


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Brian Reay wrote:

"Cecil Moore" wrote:
From "Radio Handbook" by Bill Orr, 20th edition, copyright 1975,
section/page 27.9: "The feedpoint impedance of a ground plane may
be raised to about 50 ohms by drooping the radials down at a 45
degree angle." Anyone got an earlier edition?

Not of that book, but similar wording in ARRL's 1972 "VHF Manual". I found
it, but not the book I was looking for.

You're right, page 179: "Another matching trick with the ground-plane
is to droop the radials downward, adjusting their angle below the
horizontal until the antenna feed impedance becomes 52 ohms. This
usually occurs at about a 45-degree angle."
--
73, Cecil http://www.qsl.net/w5dxp


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Radials function as a counterpoise, and, when there are enough radials, a
ground plane.

If you wish to attenuate ground losses, then it is best to make the most of the
surface by using as many radials as possible. The first dozen+ are the most
critical in reducing ground losses. Even a dozen or so helps substantially or
over 3, for example. Several dozen reduces ground losses substantially.

Elevating radials always helps.

73,
Chip N1IR

"Fractenna" wrote

Radials function as a counterpoise, and, when there are enough radials, a
ground plane.

If you wish to attenuate ground losses, then it is best to make the most
of the
surface by using as many radials as possible. The first dozen+ are the
most
critical in reducing ground losses. Even a dozen or so helps substantially
or
over 3, for example. Several dozen reduces ground losses substantially.

Elevating radials always helps.

73,
Chip N1IR


Welcome back to the group, Chip! Where have you been?

Jack Painter
Virginia Beach, Virginia

On 11 Jan 2005 22:26:54 GMT, (Fractenna) wrote:

Radials function as a counterpoise, and, when there are enough radials, a
ground plane.

If you wish to attenuate ground losses, then it is best to make the most of the
surface by using as many radials as possible. The first dozen+ are the most
critical in reducing ground losses. Even a dozen or so helps substantially or
over 3, for example. Several dozen reduces ground losses substantially.

Elevating radials always helps.

73,
Chip N1IR

Well, Chip, as the inventor (Dr. George H. Brown) said, two radials
are sufficient for a ground plane, but the RCA sales dept thought they
would sell better with four. But a ground plane antenna suffers no
ground losses, so using as many as possible only applies to radials on
or in the ground.

Walt, W2DU

"Brian Reay" wrote:

:
: I'm sure it is much older than 15 years- it was around when I did my RAE
: (more than 15 years !). I'm pretty sure it is the the old Admiralty
: Handbook, but I can't lay my hands on mine. You see a similar effect when
: making a dipole into and inverted V.
:
: It is certainly taught on at least one Advance RCE course ;-)


anyone else notice how Brian comes to the aid of
his faultering/slipping anonymous comrade ?

On Wed, 12 Jan 2005 14:41:33 -0000, "Airy R.Bean"
wrote:

Discussed in the "Antenna Manual", by Woodrow Smith,
pub "Editors and Engineers Ltd " dated 1948.

He refers to the "Brown Ground Plane Antenna" and separately
to the "Drooping Ground Plane Antenna"

But does he refer to the 'drooping' as an impedance-matching device?

If not, what reason does he give for the technique?

On Thu, 13 Jan 2005 20:05:24 GMT,
(ZZZPK)
wrote:

wrote:

: On Wed, 12 Jan 2005 14:41:33 -0000, "Airy R.Bean"
: wrote:
:
: Discussed in the "Antenna Manual", by Woodrow Smith,
: pub "Editors and Engineers Ltd " dated 1948.
:
: He refers to the "Brown Ground Plane Antenna" and separately
: to the "Drooping Ground Plane Antenna"
:
: But does he refer to the 'drooping' as an impedance-matching device?
:
: If not, what reason does he give for the technique?

capacitance is prop to gap between plates.


I think you meant that it's inversely proportional to the gap between
the plates.

Bob, W9DMK, Dahlgren, VA
Replace "nobody" with my callsign for e-mail
http://www.qsl.net/w9dmk
http://zaffora/f2o.org/W9DMK/W9dmk.html

W9DMK (Robert Lay) wrote:

(ZZZPK)
wrote:
capacitance is prop to gap between plates.

I think you meant that it's inversely proportional to the gap between
the plates.

I've made the same mistake - said "capacitance" when I really
meant "capacitive reactance".
--
73, Cecil http://www.qsl.net/w5dxp


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