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