Followon to image theory
 

"Roy Lewallen" wrote in message
...
The responses from the professors frankly baffle me. If that's what they
said, and if they meant what you think they mean, then yes, I disagree
with the professors. Folks will have to decide whether to believe them, or
me, or learn more about antenna operation so they can come to their own
informed conclusions.

I won't comment on the Navy training manual, recalling some of the
simplifications made in the equivalent Air Force documents in an effort to
make electronics understandable by the target audience.

Roy Lewallen, W7EL

I am also very familiar with the Military's method of training. even the FAA
does the same thing. They are trying to train a group of people that just
walked in off the street and a test said they had an aptitude to learn
electronics. In reality they may have no previous knowledge at all. All of
this training must take place in a few months so shortcuts in explaining it
may be taken, math used is often limited to an 8th grade level. Believe me
military training manuals are not the gospel of electronics but they are a
very good place to start without a pre-engineering prerequisit.

Followon to image theory
 

Jimmie D wrote:
Believe me
military training manuals are not the gospel of electronics but they are a
very good place to start without a pre-engineering prerequisit.

Does military current still flow from minus to plus?
--
73, Cecil http://www.w5dxp.com

Followon to image theory
 

"Cecil Moore" wrote in message
t...
Jimmie D wrote:
Believe me military training manuals are not the gospel of electronics
but they are a very good place to start without a pre-engineering
prerequisit.

Does military current still flow from minus to plus?
--
73, Cecil http://www.w5dxp.com

They did in the mid 70s. We have a newbie at work that just got out of the
Navy and was showing me his training books, I will ask him.I always
considered flow from + to - becasue it make dealing with solidstate easier
even though I was taught - to +. Also I always remembered they said it
flowed from - to + to answer their irrelavent questions.Last I heard an
electic current was a flow of cuurent carriers tha tcould be electrons or
holes flowing in opposite direction, to me it is mox nix.

Jimmie

Followon to image theory
 

When I read many academic books on antenna theory, most of them appear to
say that the radials reflect the radio wave emitted by the vertical. I do
not think that I am reading the books out of context. The replies from two
professors of antenna theory indicate that they believe that the radials
reflect the radio wave and form a mirror image.

Looking at the vertical monopole with four radials, I suspect that Douglas
Miron is correct in his book. He says that the radials radiate but have
horizontal cancelling fields.

I would expect the radials to radiate because current is forced through them
by the RF generator. The current splits between the radials, thus causing
the fields to cancel in the horizontal direction. The fields probably have
an effect in the vertical direction, causing a change in radiation pattern
and affecting angle of radiation.

I am not sure whether the return current through the radials causes any form
of mirror image. On a PCB track above a ground plane, the current returns
through the ground plane via the path of least impedance which is often
directly underneath the PCB track. The PCB track is the positive voltage
side. The ground plane current is the 0V side. It is said that the current
in the ground plane mirrors that flowing through the PCB track.

Followon to image theory
 

Elevated radials do radiate. However, assuming a symmetrical structure,
the radiation is minimal (assuming there's another normally radiating
conductor in the system) because the fields from the wires nearly cancel
in all directions. At right angles to the plane of the radials and along
the center line, the cancellation is complete and radiation zero --
again assuming a perfectly symmetrical structure. In a typical ground
plane vertical system, the contribution to the total field from the
radials is minimal, in any direction.

Anyone interested in the pattern could model a radial structure by
itself, with a source in each radial wire at the common junction. In the
absence of loss, the model would radiate the entire amount of power fed
to it, so it wouldn't be representative of the amount of contribution to
the total field which the radials provide in a conventional ground plane
type antenna. But it would show you the shape of the field radiated from
the radials. I did this out of curiosity for two radials -- the pattern
is a volume of revolution of a cloverleaf 2D pattern.

The radiation from buried radials is much less yet due to the lossiness
of the ground.

There's no point in my commenting further on the concept of a few
radials as a "mirror".

Roy Lewallen, W7EL

David wrote:
When I read many academic books on antenna theory, most of them appear to
say that the radials reflect the radio wave emitted by the vertical. I do
not think that I am reading the books out of context. The replies from two
professors of antenna theory indicate that they believe that the radials
reflect the radio wave and form a mirror image.

Looking at the vertical monopole with four radials, I suspect that Douglas
Miron is correct in his book. He says that the radials radiate but have
horizontal cancelling fields.

I would expect the radials to radiate because current is forced through them
by the RF generator. The current splits between the radials, thus causing
the fields to cancel in the horizontal direction. The fields probably have
an effect in the vertical direction, causing a change in radiation pattern
and affecting angle of radiation.

I am not sure whether the return current through the radials causes any form
of mirror image. On a PCB track above a ground plane, the current returns
through the ground plane via the path of least impedance which is often
directly underneath the PCB track. The PCB track is the positive voltage
side. The ground plane current is the 0V side. It is said that the current
in the ground plane mirrors that flowing through the PCB track.

Followon to image theory
 

Cecil Moore wrote:

Does military current still flow from minus to plus?

I believe electron current still does. But it doesn't really matter.
It's just that I really hate having to explain thermionic emission
as a process whereby heating the cathode causes charge to be emitted
from the anode. :-)

73 de ac6xg

Followon to image theory
 

Jim Kelley wrote:
Cecil Moore wrote:
Does military current still flow from minus to plus?

I believe electron current still does. But it doesn't really matter.
It's just that I really hate having to explain thermionic emission as a
process whereby heating the cathode causes charge to be emitted from the
anode. :-)

Just throw in a little relativity.
--
73, Cecil http://www.w5dxp.com

Followon to image theory
 

"Roy Lewallen"
Elevated radials do radiate. However, assuming a symmetrical structure,
the radiation is minimal (assuming there's another normally radiating
conductor in the system) because the fields from the wires nearly cancel
in all directions. At right angles to the plane of the radials and along
the center line, the cancellation is complete and radiation zero --
again assuming a perfectly symmetrical structure. In a typical ground
plane vertical system, the contribution to the total field from the
radials is minimal, in any direction.
________________

Here is a link to a NEC-2 study I did about a month ago for a broadcast
board, based on this configuration. Roy, I'd be grateful for your comments
if you see anything you don't agree with there.

http://www.freefilehosting.org/publi...60%20Plots.pdf

RF

Followon to image theory
 

With a vertical monopole antenna, the field emitted by the radials forms a
near field and interacts with the wave radiated by the vertical element. Is
it mainly in the vertical direction that the radial fields interact with the
field from vertical element? I would expect the antenna feedpoint impedance
to be formed from the length of antenna conductors and the interaction of
the fields.

If a monopole is simulated in a NEC program above a perfect ground plane, is
it possible to see the reflection? I would expect NEC program to show
reflection of waves from metallic surfaces e.g reflection from perfect
ground plane or parabolic dish. Can a NEC program allow the user to see
whether the wave is reflected (as for perfect ground plane) or whether
effect is due to wave interaction (as for radials)? Can the user then vary a
finite size ground plane to see whether antenna impedance comes from
reflection or wave interaction?

Followon to image theory
 

David wrote:

With a vertical monopole antenna, the field emitted by the radials forms a
near field and interacts with the wave radiated by the vertical element. Is
it mainly in the vertical direction that the radial fields interact with the
field from vertical element?

The fields "interact" wherever they exist.

I would expect the antenna feedpoint impedance
to be formed from the length of antenna conductors and the interaction of
the fields.

You should also expect the feedpoint impedance to be formed by the
ratio of the voltage to the current at the feedpoint, among other things.

If a monopole is simulated in a NEC program above a perfect ground plane, is
it possible to see the reflection?

Only on Groundhog Day. :-)

I would expect NEC program to show
reflection of waves from metallic surfaces e.g reflection from perfect
ground plane or parabolic dish. Can a NEC program allow the user to see
whether the wave is reflected (as for perfect ground plane) or whether
effect is due to wave interaction (as for radials)? Can the user then vary a
finite size ground plane to see whether antenna impedance comes from
reflection or wave interaction?

An interactive video game it's not. Perhaps if you were to become a
NEC user, you would come to know these things and more, first hand.

Jim, AC6XG