Richard Clark wrote:
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.

Well, you couldn't be radiating 100 watts in both cases if the field
strength is the same above the center line, but half the field is
missing in one of the cases.

But regardless of the radiating structure, if 100 watts at 40 M is
being radiated, you are launching about 2*10^28 photons per second.

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.

Hence the stipulation that the field strength above the centerline
being constant, rather than the radiated power. I missed that we were
only talking about a case of radiating 100 watts.

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

Not much to discuss. I don't do such calculations often, but I get
about 5*10^-27 joule per photon. What do you calculate their energy
to be?

No, I suppose not.

Do you have some point?

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

Sure. That will take us back to how an elevated radial system gives a
different vertical pattern than an actual ground plane or a lossy
ground does. You go first.

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

You have to start understanding mirrors, somewhere. Perhaps you
prefer a different starting point. There are several.

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.

I have no idea what you are saying with these two sentences.

wrote:
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.

Awe, you ruined the suspense.

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.

Richard Clark wrote:
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

How many photons does it take to make a Watt?
73,
Tom Donaly, KA6RUH

Tom Donaly wrote:

How many photons does it take to make a Watt?

1/(Hz*6.63*10^-34).

The lower the frequency the less energy per photon.

wrote:

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


How much not true? I expect you're right, but you could make the
same argument that a two wire transmission line radiates because the
wires don't occupy exactly the same physical space. Reg made the
same point, but didn't provide any numbers, so, according to his
own philosophy he doesn't understand the problem.
73,
Tom Donaly, KA6RUH

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

If the radials are horizontal and radiating, why is
there virtually no horizontally polarized radiation?
--
73, Cecil http://www.qsl.net/w5dxp

John Popelish wrote:
Remember, it is Cecil, not me, who demands agreement or eternal verbal
torture.

I don't demand agreement, John, just resolution.
--
73, Cecil http://www.qsl.net/w5dxp

wrote:
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.

Not true.
There is always an angle and direction where the fields do not fully
cancel.

Funny, I don't see "fully cancel" anywhere in my posting.
I probably should have said "tend to cancel".

A free space vertical with horizontal radials in EZNEC
has horizontal radiation more than 40 dB down from the
vertical radiation. That's a high degree of cancellation.
--
73, Cecil http://www.qsl.net/w5dxp

Tom Donaly wrote:
wrote:

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.

Not true.

How much not true?

-45 DB, i.e. negligibly not true. :-)
--
73, Cecil http://www.qsl.net/w5dxp

Cecil Moore wrote:

Funny, I don't see "fully cancel" anywhere in my posting.
I probably should have said "tend to cancel".

A free space vertical with horizontal radials in EZNEC
has horizontal radiation more than 40 dB down from the
vertical radiation. That's a high degree of cancellation.


The issue is the horizontal opposing radials only have that degree of
cancellation for perfectly horizontal directions.

You will be able to see your statement isn't true if you place the
antenna in freespace and look at pattern distortion at various
elevation angles. For example, the 2-d plot is skewed 2.11 dB from
being circular at - 45 and +45 degrees elevation. The skewing gets
worse at larger angles from the plane of the radials.

If the radials were REALLY radiating -40dB in all directions as you
wrongly assume, there would NOT be significant FS change in the azimuth
pattern at various elevations.

You looked at horizontal radiation, but the horizontal radials peak
radiation is vertically polarized and nearly off the radial's ends.
(Just like in a dipole pattern.)

The radials do indeed radiate enough to change the pattern a
significant amount (but not at zero degrees), but the largest problem
is decoupling the feedline shield. The fewer radials are used, the
bigger the problem becomes.

There are VERY good reasons everyone settled on four radials, and it
isn't the old wive's tale about making the antenna look good. Four
radials is a reasonable compromise between excessive common mode
problems and tolerable common mode feedline current problems, pattern,
and cost.

Don't feel bad though Cecil. Many people miss this point, even card
carrying Mensa members.

73 Tom