On Feb 16, 10:05*am, Cecil Moore wrote:
On Feb 15, 3:25*pm, Michael Coslo wrote:

Is this the ultimate waaayyy off center dipole? I'm assuming the
feedline radiates a LOT.

Historically, a Zepp has been defined as a 1/2WL wire end-fed with
1/4WL of parallel feedline, a single-band antenna. MFJ sells such HF
antennas modified for 50 ohm feed. The 1/2WL end-fed wire has a very
high feedpoint impedance thus minimizing the current at the feedpoint
and minimizing the absolute magnitude of imbalance (but not the
percentage of imbalance). For instance, the current for 100 watts into
a 5000 ohm feedpoint impedance is 141 ma., a magnitude less than the
1.41 amps into 50 ohms for the same 100 watts. Seems to me, the low
current at the feedpoint, which can be considered to be common-mode,
ensures a current minimum for both differential and common-mode
standing waves.

P.S. A Double Zepp is the same thing as a 1WL center-fed dipole.
--
73, Cecil, w5dxp.com

"ensures a current minimum for both differential and common-mode
standing waves..."

I don't think it guarantees it. Consider the case of end-feeding a
"fat" half-wave-resonant antenna, like a cage or what I recall used to
be called a "flat-top" with several wires running parallel in the same
horizontal plane, connected together at the feed end (at least).
Consider feeding it with high impedance (600 ohm) open wire line. The
data I have suggests it's possible to have a feed line impedance
higher than the feed-point impedance of the end-fed half-wave (fed
against the counterpoise represented by the feeder). In that case,
the differential load impedance at the end of the feed line (the feed-
point impedance of the antenna) is lower than the feed line
differential impedance, and we must be at a maximum current point on
the feed line.

Admittedly, it's not a case you'd run into very often, but it appears
to me to be quite possible.

Cheers,
Tom