Had to look at a Windom, couldn't remember exactly what it was. I knew
somebody would have a single antenna that did DC to daylight and need to match
it to their rig. I am fortunate now and have at least one if not two antennas
on each band so I don't have to compromise as much.
We are actually talking about two different things. The Windom looks like it
uses part of the feed line as part of the antenna so needs a brute force choke
to decouple the feedline and keep that part of the feedline as part of the
antenna instead of bringing it into the shack. It doesn't look like that choke
does any of the impedance transformation or balanced to unbalanced
transformation that a transmission line tranformer (balun) does except through
brute force choking on the coax shield. So it would need only have enough
inductance to isolate and not so many turns that it goes resonant before
getting above the range of frequencies at which you use the antenna. If the
choke works at your lowest frequency it will have even more impedance at the
higher frequencies until it hits self resonance.
The transmission line transformer (balun/unun) can very efficiently isolate,
transform impedance, and tranform from balanced to unbalance within a
limitation of impedance ranges and frequency ranges while the choke operates as
an inductor having impedance until it hits the self resonant frequency
(inductive reactance of coil equals the inter-turn capacitive reactance) so it
essentially decouples the rest of the feed line from the antenna. I would say
that the Windom antenna starts at the choke and not at the center insulator.
Balun probably is the most misused word in ham radio, it has come to mean
almost any bump on the line between the transmitter and antenna regardless of
whether it is a choke, balun, unun, transmission line tranformer, length of
feedline, insulator, etc. I know I am guilty of interchanging balun and unun
all the time, its just that balanced to unbalanced transmission line
transformer is so long to say and type.
Earl
N8SS
--- towertalk-request@contesting.com wrote:
------------------------------
Message: 4
Date: Mon, 4 Jul 2016 19:26:52 -0400
From: Hans Hammarquist <hanslg@aol.com>
To: towertalk@contesting.com
Subject: [TowerTalk] Fwd: Fair rite materials for choke baluns
Message-ID: <155b83c5c4e-5f71-ee7e@webprd-m04.mail.aol.com>
Content-Type: text/plain; charset=utf-8
I have to answer you here, Earl:" I'm using a Windom/Longwire antenna. I can
tune that to 160m - 10m easy. I can even load it up on 6m although I'm still
waiting for a QSO there."
As I am "balancing" my feed line, or more correctly, am reducing the RF in my
shack by putting a choke between the tuner and the radio (the "output" that is
the end facing the TRX is well grounded for further reduction of RF in the
shack) I am depending on maximum available Z in the choke all the way from 1.8
MHz to 29.7 MHz.
I am presently relying on a choke made of 50 feet of RG58 wound on a 4 inch PVC
pipe. I am using a variable pits to avoid a specific resonance and thereby
achieving a reasonably wideband, high Z. The choke is about 12 inch long.
Hans - N2JFS
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