Agree 100%. I use a 160 meter dipole center fed with 600 ohm line and a
balun where it enters the house. From the balun it goes to a 238 tuner.
I've tried several types of balun and finally settled on a choke balun
consisting of 21 ft of RG913 wound on a 4 inch PVC pipe.
It's head and shoulders better than anything else I used. I also have a 40
meter horizontal loop (180 ft of #12 at 20 feet above the ground) also fed
with 600 ohm to the shack, then from there through 450 ohm ladder line to a
KW Johnson matchbox. The matchbox works great except that the range is a
bit limited. Tunes better with the 238, but I like the convenience of use
the 238 on 80 and the matchbox on 40 and not having to tune either when I
switch bands.
Dave K5WNV
-----Original Message-----
From: tentec-bounces@contesting.com [mailto:tentec-bounces@contesting.com]
On Behalf Of Jim Brown K9YC
Sent: Friday, April 11, 2008 5:37 PM
To: Discussion of Ten-Tec Equipment; Stuart Rohre
Subject: [TenTec] Twinlead and Balanced Tuners
I strongly urge anyone using or considering balanced feedline and
and/or a balanced tuner to study the part of my RFI tutorial that
talks about antennas and balance. Almost any ham antenna is likely
to be at least a bit unbalanced by its surroundings -- trees,
buildings, ground slope, antenna length -- even with a balanced
feedline. While the "skew" of the pattern may be minimal, the
NOISE pickup on the feedline will usually NOT be minimal. This
noise pickup is caused by common mode current, which is the result
of antenna imbalance. Killing this common mode feedline current is
a major benefit of a good choke balun (W2DU or better).
The coaxial choke baluns described in my tutorial are MUCH BETTER
choke baluns, because they present a MUCH higher common mode
impedance. Because all forms of twinlead have significant leakage
flux that heats a ferrite core, it is NOT practical to wind a
choke with twinlead. This is a MAJOR disadvantage of feeding
antennas with twinlead.
http://audiosystemsgroup.com/RFI-Ham.pdf
http://audiosystemsgroup.com/NCDXACoaxChokesPPT.pdf
A FAR better way to do it is to use big coax to keep losses low
(RG8 if it's a low dipole, RG11 if it's a high dipole) and a good
tuner. The 229 and 238 tuners are EXCELLENT tuners (very good
efficiency, very good tuning range). My 80/40 fan dipoles are all
within 3:1 on 30, 17, and 12 meters, and work VERY well with a
238. I can't easily install a tri-bander on a tower, so I use
20/15/10 fan dipoles. All of these antennas have serious coax
chokes at their feedpoint, and they are very quiet on receive.
Quite a few members of NCCC and PVRC (two premier contesting
clubs) are using my chokes on a variety of antennas, and report
similar results.
IMO, the benefits of twinlead feeding an all-band one-size-fits-
all wire dipole are a fignewton of the imagination of guys who are
casual operators and don't do much weak signal work. They ARE an
EASY way to work all bands, but they are NOT a GOOD way to work
all bands.
73,
Jim Brown K9YC
On Fri, 11 Apr 2008 14:36:31 -0700, Stuart Rohre wrote:
>On the subject of the tuner being balanced itself
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