AndyS wrote:
Joel Kolstad wrote:

"AndyS" wrote in message
groups.com...

The radiating element, which you are measuring, has to have a
counterpoise (ground) to establish the Efield against and an Hfield
around.

I believe that -- at least from a mathematical perspective -- "infinity" is a
perfectly good counterpoise. (Just as isolated conductors have capacitance to
infinity and inductors have "partial inductance" whereby a return path at
infinity is assumed.)

As a practical matter, of course the user's hands and other objects in the
environment will affect the measurement, but suggesting that "one must always
have a well-defined counterpoise" would tend to discourage one from studying
antennas that are less sensitive to counterpoises than those that are, and
this endeavor is quite valuable for the design of miniature antennas. After
all, there are millions of commercial devices in operation every day for which
the counterpoise is ill-defined.


Andy comments:
Yes... well... maybe..

In order to propagate, the Poynting vector has to have an Efield and
an
H field. The E field is between the "wire" and it's
counterpoise....specified
in V/M .... that is the voltage between the two divided by the
distance
between them...... As an aside, the orientation of the Efield is the
polarization of the antenna --- vertical, circular, horizontal,
elliptical, etc....

Now, if the counterpoise was at infinity, the Efield must always be
zero,
since any voltage divided by infinity ( to give V/M) will be zero.
Hence there
can be no propagation...... Like connecting up to one terminal of a
battery..

All antennae, even the very inefficient ones used in "commercial
devices",
have a hot side and a ground. If the ground is well defined, as in a
patch
antenna, the field and radiation characteristics are well defined. If
the
counterpoise is simply a ground track on the PC board, it is fairly
well
defined, but the radiation is, well, squirrelly. Fortunately, a
matching
circuit assures that power will be radiated, even if the field is not
pretty.

Loop antenna, which do not work against a ground plane, use one of
the two feed points as a counterpoise. Such antennas are easier to
visualize using H fields, tho, as before, one MUST have and E and an
H field for it to actually work.... The Efields of a loop exist
between
sections of the loop as a function of the current flow thru the loop,
and
don't give much of an intuitive feeling...... but I digress...

If you know of an antenna that has no counterpoise for the "hot"
side to
work against, please post some information about it...... However, in
my
experience, it would be like having a magnet with a North pole and no
South pole ---- ain't no such thing..... Yet, I'd be glad to learn
if you
would care to teach.....

Andy W4OAH

PS And I would be very interested if Roy LeWallen would step in here
with an opinion. He has done more antenna stuff than I have,
and
may be able to explain it better..... I know he hangs around
this
group since I have seen his posts . :))))))




Where is the counterpoise on a handheld transceiver? I believe it is the
body of the transceiver, the hand, arm, and body of the operator, and the earth.

The data in this thread was in response to an earlier thread of the same
subject. That's why I added "-followup" to the subject for this thread.
Please read that thread originally posted on 7/7/2006 at 2:29PM. The
following will make more sense if you read that original thread.

If you assume the MFJ is the body of a handheld transmitter, which it is,
then these results show how a quarter wave whip reacts to a handheld
transceiver having a metal enclosure. The counterpoise for a handheld is its
metal chassis but usually separated from the operators hand by a plastic case.

In the original thread, there was posted links that are now broken
(7/9/2006, 11:37AM). As I recall one of the items appeared to be a whip on a
camera. I think the other one was a whip on a radio. So, I tried to make
some measurements to show how much variation there can be with wire antennas
and to underscore the fact that there is no way anyone can predict what a
wire antenna's impedance will be on the objects the OP referred to under the
myriad of conditions possible.

Cheers,
John