On 19 Jul 2006 16:12:38 -0700, "AndyS" wrote:


Joel Kolstad wrote:

If I take a charged sphere with 1V applied, the E field falls off as 1/R all
the way out to infinity; it is only there that it's actually zero, yes?


***** One volt with respect to what other point ??

The RF generator
which drives the antenna has TWO terminals. If one terminal is
connected
to the wire, or the sphere, the OTHER terminal must be connected to
something else for the antenna to radiate. Hence, one terminal is
connected
to one side of the antenna, balanced or unbalanced, and the other
terminal is connected to either the other side of a balanced antenna,
or
some other structure such as a ground plane or counterpoise......
Remember, all RF generators are TWO terminal devices, and the
voltage is the voltage between the two terminals, not between one
terminal and some other point located on Mars.......
This potential difference sets up an Electric field, and the attendant
electron motion sets up an H field, and thus an energy wave
propagates.......


How about a half-wave antenna (end-fed zepp)? Assuming it's being fed by
coax, would you suggest the counterpoise is the ring making up the shield of
the coax right where the coax stops and the antenna starts?

***** End fed Zepps radiate from the feedline as well as the driven
element,
and usually open wire line and not coax is used as a feed. I've
never
seen a coax fed Zepp, tho I think it would probably work OK with
the
proper matching at the transmitter.... The coax shield is part of
the

The coax or balanced line is not the radiating system the though it
may interact some it's the matching network from the low (under
600ohm) to high (3000ohm) impedence at end of the halfwave
antenna.

Coax can be used but since one end is mismatched from it's
characteristic impedence it could be lossy. Usually it's not as the
matching section is small (~1/4 wave). In practice it works very
well and there are antennas like Spertof (sp??) and other coaxial
fed antennas are very succcessful.

Allison



radiating system, as you can verify with an EZNEC simulation and
looking at the pattern... The Zepp is just a version of a dipole.
The ARRL handbook tells all about the difficulty of matching
the Zepp as a result of feedline radiation.....

***** Dipoles have one half of the antenna connected to one terminal
of the RF generator and the other hald of the antenna connected to the
other terminal.... If link coupling is used, neither part of the
antenna is
connected to the generator, but to a transformer, which then becomes
the
"new" generator output....... I have never seen any system at all,
in any
book, that uses a one terminal RF source, ----- there ain't no such
animal.
It's like a one terminal car battery....... saves connectors but won't
start the car...
:))))))))

--- and I have used the coax as half of a radiating dipole simply by
looping it thru some ferrite at a quarter wave from the feed point.
A wire is half the dipole and the coax feedline is the other half.....
It
ain't rocket surgery to use the coax outer shield as a radiating
structure....
If the dipole is mounted vertically, you have what can be advertised as

a "no ground plane" vertical.....---- the radiating portion of the
feedline
forms half the dipole.....


***** Perhaps we are merely disagreeing on semantics. That's OK....
My stuff works --- your stuff works...... Maybe we just look at things
differently........ I suspect it's too late for either of us to want
to change
our understanding of how the world works... :))))))

Andy W4OAH


I would like to hear from someone like Roy as well, since I certainly am
well outside of any areas of significant experience here.

---Joel


***** Yeah.... Where's Al Gore now that we need him ??? :)))))))

AndyS wrote:
John - KD5YI wrote:

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.


****** Yes. If the case is conductive. Even if the case is metal ,
and not
connected to the internal "ground" , it becomes part of the
counterpoise
by capacitance. Of course, the hand is conductive, etc.....


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.


\
**** And you did that very effectively. I didn't realize that you were
trying
to show the significant variations, and thought you were wondering why
the readings were so different. Sorry,.... I just didn't get your
intent....

I would have liked to see what the piece of wire did with a nice ground
plane, tho, to see what the design baseline would have been.... In
other words,
a piece of wire looks like, say 32 ohms over a ground plane, but when
all the variables such as shape, no ground plane, people, nearby
objects,
etc come into play, it goes from hell to high water.....
I'm glad to see someone actually doing the experiments, rather than
just quoting a bunch of " E to the J Beta pitchforks" and letting it
go at that....... :)))))

Andy W4OAH


Thanks for your comments, Andy. I agree with you on experiments. There are
times, however, I would rather experiment using EZNEC than with the MFJ. It
all depends on circumstances. One method can be faster than the other
depending on the goal.

In fact, it has been between 105 and 108 degrees here for the last week or
two, putting a crimp in outside activities. I would rather stay inside and
model my unusual thoughts than to try them outside. On the other hand, I
don't know how to model an MFJ enclosure, my hand, my body, and such in
EZNEC. So, that is when I measure.

Also, there are times when both methods are warranted. Like, measure to
determine if your model is correct. Or, model to determine if your test
set-up is correct.

Each method has its advantages and disadvantages. I just hope I have the
knowledge to choose the appropriate method when it comes time to do the work.

73,
John