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 ??? :)))))))