[Elecraft] Counterpoise on 1/2 wave long wire

[Stuart Rohre]

Ron, the counterpoise action does not depend on the end point only.  There
has to be a resonance developed ie, a physical length to accommodate the
cycle of the wave at the frequency being used.

However, to back up to the beginning, why a counterpoise with a HALF WAVE
antenna?   HALF WAVE antennas form a resonant dipole and the wave has all
the length it needs to develop the full current distribution to cause
radiation action.

A HALFWAVE antenna out in space is fully functional without a counterpoise,
radials, or anything besides its feeder.

Only if you have very poor earth at your location, and need a ground mounted
counterpoise to enhance earth reflection gain for the dipole half wave,
would you need to include a counterpoise.  Look in the ARRL Handbooks, or
Antenna Book, and they show the voltage and current distribution on various
antenna lengths.  See the full cycle of current that develops along the
entire half wave of wire?  That is all it takes for the antenna to radiate.
There, in that full cycle of current we see two discontinuities, (the ends
of the half wave of wire).  We see the direction of the current change at
the mid point of the half wave.   For radiation to happen, W8JK, John Kraus
writes in his classic, "Antennas", that you need a discontinuity or change
of direction.

A radial or counterpoise or ground plane exists to augment an antenna of
less than a half wave or multiples of a half wave long.  It becomes part of
the antenna system.

HALF WAVE long physical antennas are earth independent; little is gained by
adding radials, counterpoises, or ground screen to them.   Unless, you are
trying to beam something straight up, and get a short distance hop
reflection from the ionosphere.  That special application for instate HF
communications, is known as Near Vertical Incidence Skywave, and is enhanced
by low dipoles, and either ground reflection or reflection from a
counterpoise directly parallel and under the Half Wave dipole.  For proof of
these statements, look at the noted antenna expert, W4RNL's web site:
www.cebik.com  L. B. Cebik has modeled the half wave extensively as well as
other lengths of antennas and noted the need or lack of need, for augmenting
various antennas with other structures that might enhance radiation.
(Radials, counterpoises, ground planes, screens, etc.)

Hope that helps clarify antennas for you.
-Stuart
K5KVH