Additional response to OP jo9s8as at yahoo.com:

Using an MFJ259B with a #14 AWG (.064 dia) copper wire 19.4 inchs long stuck
into the antenna connector, I measured the following...

f = 146.5 MHz
R = 64 ohms, X = 65 ohms
both hands holding the MFJ

f = 146.5
R = 43 ohms, X = 60 ohms
one hand holding the MFJ

Sat the MFJ down on a brick wall about 3.5 feet high and moved away from it.

f = 146.5
R = 34, X = 44

Same location, adjusted for minimum SWR

f = 153 MHz
R = 61, X = 25

This last reading was a bit difficult as the readings changed with my body
location.

I could never determine the sign of the reactance for sure and I was never
able to adjust the frequency so that the reactance reading was lower than
about 25 ohms.

The MFJ enclosure is about 6.75 x 2.375 x 4 inches.

Cheers,
John

John - KD5YI wrote:
Additional response to OP jo9s8as at yahoo.com:

Using an MFJ259B with a #14 AWG (.064 dia) copper wire 19.4 inchs long stuck
into the antenna connector, I measured the following...


Andy comments,
John, your results would be more consistent, and more meaningful,
if you had some sort of ground plane in your experiments.

A wire, by itself, with nothing else, is like trying to light a lamp
with
only one prong plugged into the socket......

The radiating element, which you are measuring, has to have a
counterpoise (ground) to establish the Efield against and an Hfield
around.
In your setup, the housing of the MFJ, and your hand, and probly
other stuff, is the counterpoise, and the results are inconsistent.
I suspect that if you took a measurement, and started to pee on the
ground, the reading would change (grin).......Try it. But keep the
power low :))))

So, while your experiments may give you an idea of what the
resonant frequency and impedance of a piece of wire is, unless you
are able to take consistent, repeatable measurements, you can be
sure that something is not being accounted for..... My suggestion
is that you need a good counterpoise...... Maybe buy a sheet of
corrugated tin from Home Depot, mount the connector in the middle,
with the MFJ on one side and the antenna wire on the other.... You'll
find, I am certain, that your readings will be more consistent.....

This is not a bad ground plane for 2 meters --- I have used one
with good results......

It ain't magic, but there isn't any such thing as a unipole
radiator....

Good luck,

Andy W4OAH

"AndyS" wrote in message
oups.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.

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

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


Cheers,
John

My suggestion
is that you need a good counterpoise...... Maybe buy a sheet of
corrugated tin from Home Depot, mount the connector in the middle,
with the MFJ on one side and the antenna wire on the other.... You'll
find, I am certain, that your readings will be more consistent.....

This is not a bad ground plane for 2 meters --- I have used one
with good results......
==========================
Alternatively you could use a ground plane of chicken wire mesh ,a bit
easier to handle than a sheet of metal.

Frank GM0CSZ / KN6WH

Highland Ham wrote:
==========================
Alternatively you could use a ground plane of chicken wire mesh ,a bit
easier to handle than a sheet of metal.

Frank GM0CSZ / KN6WH

Andy comments:
That's a good idea. I always seem to have some tin laying around
and
no chicken wire, but it would work well. Also hardware cloth -- that
stuff
with the little squares that is used a lot on rabbit cage bottoms.....

In fact, they would both be good for corner reflectors, with a PVC
frame...
Or a large bowtie dipole to get broadband at VHF........ hmmmmmmmm.

Thanks Frank, you have ALMOST inspired me to start another
project........... maybe tomorrow :)))))

Andy W4OAH

Hi Andy,

"AndyS" wrote in message
ups.com...
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.

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?

If you know of an antenna that has no counterpoise for the "hot"
side to
work against, please post some information about it......

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?

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

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 Zepp antennas I have come across are fed with a balanced feeder.

Frank GM0CSZ / KN6WH

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
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 ??? :)))))))