[Antennas] How to calculate 50 ohm point?

Sat May 19 10:29:03 EDT 2012

Ray, - More -
The REAL Zeppelin Antenna was designed for use on the
Hydrogen-Filled airships. They caught on fire easily, so the
antenna was designed to keep the high voltage far away
from the airship frame and surface. They knew about the
1/2 wave antenna, and the High Impedance, (read high
voltage), feed for them, and they knew about the Impedance
and voltages to be found on a parallel-wire transmission
lines. They let their half-wave single-wire antenna hang way
down below the airship, and fed it with the appropriate
length of parallel transmission line. The low Impedance end
of their quarter wave, or odd multiple thereof, connected to
the transmitter, which I expect contained the L and C for the
transmitter Final Amplifier "Tuner". That is a real ZEPP.
One of my favorite HF antennas is a Dipole, fed in the center
with a 300 Ohm Twin Lead, Balun and tuner in the shack.
It's a dipole. Some partially educated communication
engineers call it a "Double ZEPP". They do that mostly
because they don't know what a real ZEPP is.
73 Clete
+++++++++++++++++++++++++++++++++++
P.S. To feed that conglomeration with 50 Ohm Coax
you want to place a short at the bottom end of the 1/4
line, and attach the coax up a few inches, or more,
from the bottom, such as they do with the "J-Pole"
on 2 Mtrs. The J-Pole being a miniature ZEPP
standing on its end.
Like this:
.
Z
E
P
P
.
73 Agn
++++++++++++++++++
On 5/19/2012 9:41 AM, C.Whitaker wrote:
> de WB2CPN
> IF the 1/2 wave is cut to 468, (subject to a slight tweek),
> and hanging free of trees and/or structures, AND the
> vertical 1/4 wave is low loss, (10 inches air spacing),
> cut to half the value you used for the 1/2 wave, it will
> come out close enough to the Z of the 1/4 wave section.
> That could be about 400 to 600 Ohms.
> I would but a 4:1 balun at the bottom of the 1/4 wave,
> and use a tuner, which may or may not be needed.
> Try it.
> 73 Clete
> P.S. I expect you will receive varying opinions on this.
> +++++++++++++++++++++++++++++
>>> On 5/18/2012 1:33 PM, Ray wrote:
>> Does anyone know how to calculate the expected 50 ohm point near the
>> shorted end of a 1/4 wave coaxial stub made of 66% VF cable.
>>>> I will be end-feeding a 1/2 wave antenna. The open (antenna) end of the
>> stub will be lightly loaded and have a quite hi Z.
>>>> Your attention is appreciated.
>> Ray, W4BYG
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