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VK3ABK > HELP 04.04.07 09:34l 79 Lines 3443 Bytes #999 (0) @ WW
BID : 53936_VK3HEG
Read: GUEST
Subj: More 1/2 wave end fed...
Path: DB0FHN<DB0MRW<DB0RGB<OK0PPL<DB0RES<DK0WUE<CE8FGC<VK6HGR<VK4TRS<VK3HEG
Sent: 070404/0502Z @:VK3HEG.#WEV.VIC.AUS.OC #:53936 [Ballarat] $:53936_VK3HEG
From: VK3ABK@VK3HEG.#WEV.VIC.AUS.OC
To : HELP@WW
Hello again dipoles.
That's a greeting from an earlier bulletin.... But there's no doubt about it;
Ray, VK2TV, Neil, ZL1ANM and I seem to be on the same wavelength!
Before I read Ray's enlightening 'Zepp' bulletin, I had, again, retrieved
a bulletin from the past when we were discussing antennas and I compared the
J Pole antenna to the Zepp. He, and now Neil, have covered the topic well,
but a further comment may not be out of place.
I had sent....
Portable antennas for HF can be a random length of wire or a resonant dipole.
If you can't or don't want to use a dipole, an end fed antenna may be the
answer. One that has been around for ages, is the end fed Zepp. This antenna
will have a high impedance feed point whether it is resonant or not.
Here is a diagram showing the general idea...
Counterpoise Long wire antenna
X
ÄÄÄÄÄ¿ ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄ//ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ This type of antenna
Short length³ ³ when used on airships
of wire. ³ ³ became known as a Zepp
³ ³ and was trailed below
³ ³ the airship.
³ ³ Amateurs and others use this
³ ³ antenna as an 'end-fed Zepp'. counterpoise
³ ³
ÚÁÄÁ¿
ATU ÀÄÄÄÙ A matching network (match-box)
is used to reflect an impedance
to point X by using the feedline
as an impedance transformer.
Now, back to the present....
As Ray has pointed out, it is just a matter or orientation. The antenna can
be fed from the end in each case, provided the correct matching circuit is
used, with consideration for the counterpoise.
Ray sent....
"Actually, if you take the two-wire feed portion of the J-pole away at 90ø
to the 1/2 wavelength section, the antenna can, and does, find horizontal
application."
Whether it is used as a resonant antenna or not is probably a personal choice
and the Zepplin operator would most likely winch out the length he found to
help his feed match.
Whatever you think best, the main point in respect to the original bulletin
from Gordon, G4TZX, is that any impedance found at the end of an antenna can
be matched to a feed line with a reactive circuit.
It is easy to design an antenna if you separate the two main requirements.
(1) Antenna length. That is, whether resonant or random length.
(2) Matching to a transmitter or receiver.
These are two separate but compatible requirements, often confused, which
should be adjusted with suitable instruments. A 'GDO' and 'SWR meter', or a
combination 'Antenna analyser' (tuner/matcher, whatever).
Anyway, read these bulletins and I hope they get you thinking.
Ps. I have just visited my garage and found the mobile whip I used for HF
some years ago. The vital parts of interest are a loading coil, adjustable
by a sliding contact for 20/40/80 metres, of 100 turns wound on a 50mm form
that screws midway (the higher the better) in a 3 metre whip. A 6 turn coil
at the base is tapped for a 50 Ohm match.
This may not be what Gordon wanted, but may interest others.
73. Dick. VK3ABK. ( And as Guggi Macaroni said, hang em high and long.:-)
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