Bill,
I use a very similar antenna system. I measure best feedline current
balance when I use an unbalanced tuner (Ten Tec 238) connected through a
very short length of RG213 to a 1:1 CM choke mounted just outside the
shack window where the window line terminates. The choke comprises 11
bifilar turns on 2 stacked FT240-52 cores, similar to Balun Designs
model 1171:
http://www.balundesigns.com/model-1171-1-1-atu-current-balun-1-54-mhz-5kw/
To illustrate Jim's point about antenna systems rarely being balanced -
visually mine appears symmetrical, however the star-network equivalent
circuit at 3.5MHz measures:
Leg1/Centre: 15.1 - j79 Ohms
Leg2/Centre: 1.6 - j109 Ohms
Centre/Ground: 30.7 + j110 Ohms
Looking at the top two impedances - Leg1/Centre & Leg2/Centre - there is
clearly some significant electrical imbalance despite the apparent
physical symmetry.
Steve G3TXQ
On 11/12/2017 21:33, k7wxw wrote:
I am putting up a centerfed doublet to cover 80 through 10 meters, focusing on
80, 40, 30, and 20 meters. I plan on feeding it with a random length of 450 ohm
window line. I have a Johnson Matchbox and Dentron Supertuner and can use
either to match the antenna to my rigs.
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