What is a Zepp antenna?

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Jason Hsu:
The term is thrown around a lot, but I don't know what it means.  Can anyone shed some light on what a Zepp antenna is?  What makes an antenna a Zepp antenna or a non-Zepp antenna?

Pete Allen:
What are trying to do, test my memory! Just joking but The Zepp first saw daylight on the Graf Zeppelin on it's round the world flight back in the late 1920's. Hence the name.

The Zeppelin Werke engineers wanted an efficient antenna that could trail behind the airship, that could be quickly adjusted for frequency, and that could easily be reeled in to reduce drag - and to reduce the possibilty of fouling something on docking or in wind.

The solution was essentially a length of parallel wire transmission line. A quarter wave back from the end, one side stops. The "radiator" is the final single wire, plus the final portion of the transmission line back from the open end.

You might think of it as a dipole, one side of which is driven by reflected currents from the open end. So take that "parallel transmission line" statement with a few train loads of salt. If the mismatch at the transmission line termination is severe enough a parallel wire transmission line will radiate like crazy!

And now that you have exercised the memory cells, I suppose I will spend the rest of the day trying to remember the designers name. He was one of the "Untermenchen" who never made it out of Belsen,  a friend of my old professor, but what was his name.

Anyhow, 73  Pete Allen  AC5E

Thomas Hamilton:
In much of the antenna literature, a half wave dipole fed in the center with open wire line is sometimes refered to as a "center fed zepp", as opposed to an end fed zepp described by AC5E.

I cannot imagine trying to trail a center fed zepp from the back of a zepplin, hi hi.

The nice thing about a "center fed zepp" is that it can be used on multiple bands with the appropriate tuner.

KA4P

Cecil A. Moore:
The original Zepp was indeed a 1/2WL monopole fed with 1/4WL open-wire line. The Zepp is 1/2WL long and therefore, according to widely accepted views, doesn't require a ground plane. The same principle applies to this very day for through-the-window mobile antennas.

A "Double Zepp" is a one-wavelength long center-fed dipole. An "Extended Double Zepp" is a 2x5/8WL dipole.

Please note that all Zepps are *single-frequency* antennas since they are defined for one, and only one, wavelength.
--
73, Cecil, W5DXP

Dale Hunt:
One of the problems with operating radios from the
Zepplins was to avoid any high voltage wire ends around
the hydrogen bags, which could have disasterous consequences.

So the half-wave horizontal wire was hung below the ship using a weight in the front end (so the feedline
hung vertical) and a windsock at the back end.  The
feedline was a quarter wave long, so the high impedance
at the antenna became a low impedance at the transmitter.
This was then fed with a series-tuned link coupler.

If one assumes that the impedance at the end of a half-
wave element is infinite, then the feedline would be
balanced since the other side was connected to nothing.
This isn't actually the case, and the feedline isn't
perfectly balanced, but, as G6XN once commented, "although
this is not a good way go get the antenna to radiate, it
is not a good way to keep it from radiating, either."

And, though certainly not perfect, it does work.  The
most common implementation these days is, of course, the
J-pole.

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