Reg Edwards wrote:
George Brown was over precautious. Only one vertical radial is
needed. There is no loss in efficiency. The radiation pattern remains
sensibly the same.

8-D

"Cecil Moore" wrote

It's pretty easy to understand. Any two radials,
180 degrees apart and high enough, should theoretically
cancel each other's radiation in the far field.
--
73, Cecil
=====================================

If they don't cancel-out each other in the near field then they don't
cancel-out each other in the far field either.

A pair of radials behave as a continuous dipole fed at its center via
a single wire. And it radiates.

A circular disk, diameter = 1/2 wavelength, fed at its centre
radiates.

But don't ask me what its radiation resistance is. It must be very
low.
----
Reg.

Ok I am getting confused. You are saying that a groundplane will not
work as good a a ground mounted vertical ? At what angle are you
talking about? Are you more interested in working 500 miles or 6,000
miles?

Ron

On Mon, 10 Jul 2006 17:57:42 -0400, John Popelish
wrote:

Hi John,

In fact a larger disk will actually raise the launch angle - hardly a
satisfactory mirror analogy.


the "mirror" produces (half of the) photons that the
full dipole would have produced.


Photons? This is CecilBabble. Mirrors as "productive" sources of
photons demonstrates the failure of analogies.

Do you deny the photonic nature of radio waves?

Hi John,

This last question is standard CecilBaiting at which he is a master.

I've made a career in photonics, so you will have to go some distance
to start offering a case that comes remotely close to their cross
application. Barring that, why introduce concepts that don't advance
the topic? The following is hardly any clearer by clinging to poor
metaphors:

I just realized that the sentence you quoted s easily misinterpreted.
When I said "the "mirror" produces (half of the) photons that the
full dipole would have produced." I meant that half as many photons
are produced, compared to the full dipole antenna that produces the
same fields above the center line. I didn't mean that the mirror
produces half of the total photons that are radiated.

73's
Richard Clark, KB7QHC

Richard Clark wrote:
On Mon, 10 Jul 2006 17:57:42 -0400, John Popelish
wrote:

Do you deny the photonic nature of radio waves?


Hi John,

This last question is standard CecilBaiting at which he is a master.

I've made a career in photonics, so you will have to go some distance
to start offering a case that comes remotely close to their cross
application. Barring that, why introduce concepts that don't advance
the topic? The following is hardly any clearer by clinging to poor
metaphors:

I guess the perceived quality of any given metaphor depends on your
mental model of the rest of the universe. Antennas and photons work
for me. If they don't work for you, I have no problem with that.

Remember, it is Cecil, not me, who demands agreement or eternal verbal
torture.

On Mon, 10 Jul 2006 19:40:59 -0400, John Popelish
wrote:
I guess the perceived quality of any given metaphor depends on your
mental model of the rest of the universe. Antennas and photons work
for me. If they don't work for you, I have no problem with that.

hi John,

It would seem that they "don't" work for you. I have no problem
shifting to a photonic dialog, but you have yet to emerge from a
rather muddy start.

Remember, it is Cecil, not me, who demands agreement or eternal verbal
torture.

I can torture with the best of them too. Choose your metaphors well
to avoid the embarrassment of Abu Graib.

73's
Richard Clark, KB7QHC

On Mon, 10 Jul 2006 17:57:42 -0400, John Popelish
wrote:

I meant that half as many photons
are produced, compared to the full dipole antenna that produces the
same fields above the center line.

Hi John,

So, proceeding along your avowed lines of Photons, one of several
questions:
Presuming 100W radiated, how many photons would that be so that we
can talk about them by halves.

Yes, that is perhaps unfair, however it demonstrates how easily the
discussion can tumble for lack of quantifiables such as that original
offering of 100W.

Should we discuss how infinitesimal the energy is in a 40M photon?
(Easily accounts for why so many are needed for that same 100W.)

No, I suppose not.

Want to get into the problems of diffraction with object lenses that
measure less than a wavelength of the photon?

Hard to escape, and makes a mess of describing mirrors too, especially
when they are skeletal approximations as well.

I can offer more thread-busters when it comes to photonics, but that
is a slam dunk. Get us rolling on one ace proposition, and I will get
back to you in a couple of hours.

73's
Richard Clark, KB7QHC

Roy Lewallen wrote:
John - KD5YI wrote:

Actually, on elevated antennas (as in the usual VHF setup), just two
quarter-wave radials 180 degrees apart is almost indistinguishable from
4 or more radials. EZNEC shows very little change in terminal impedance
and pattern by removing two radials from a 4 radial ground plane.

I once used copper tape on a window to make a ground plane vertical like
that for 70cm. It worked very well.

George Brown, the inventor of the ground plane antenna, found that only
two radials were necessary. But when his company went to sell it, the
marketing department decided that no one would buy a two-radial ground
plane antenna in the belief that it would be omnidirectional. So they
added two more to make it "look" more omnidirectional. The four-radial
ground plane persists to this day.

The real reason to use 4 radials or more is decoupling the feedline
shield.

Decoupling is very bad with two radials unless you get lucky with
feedline and/or mast length or use a decoupling aid like a common mode
choke.

On a commercial 47 Mhz GP I designed that had 4 radials, the radials
had to be isolated from the mounting and a ferrite decoupling sleeve
placed over the coax. I can't imagine how bad that problem would be
with only two radials.

73 Tom

Cecil Moore wrote:
Tom Donaly wrote:
If you can bring yourself to think in terms of
current directions and far field superposition of waves, this
behavior shouldn't be that hard to understand.

It's pretty easy to understand. Any two radials,
180 degrees apart and high enough, should theoretically
cancel each other's radiation in the far field.

Not true.

There is always an angle and direction where the fields do not fully
cancel. The problem is the spatial distance is different unless exactly
broadside to the pair.

Even 4 radials has this problem, but the more radials the less of an
issue it is.

73 Tom

Reg Edwards wrote:
George Brown was over precautious. Only one vertical radial is
needed. There is no loss in efficiency. The radiation pattern remains
sensibly the same.
----
Reg.

All you have to do is figure out how to decouple the feedline for less
cost than the cost of three additional radials and a tiny easy to build
choke.

Getting the feedline off a four radial GP is bad enough.