[Antennas] twin coax as shielded balanced line

[George, W5YR]

Gary, I will try to be as brief as possible.

1. the reason for using a balanced line to an antenna almost always comes
from the desire or need to operate the antenna on more than one band.

2. tuned feeders usually operate with relatively high SWR - up to 20:1 or
so.

3. coax tuned feeders - balanced or not - have much higher loss under high
SWR conditions than does conventional ladderline or oper-wire line.

Bottom line: for multiband use - which means tuned feeders with usually
fairly high SWR - twin-coax is not the way to go unless (a) the feeders are
very short and/or (b) you need the shielded coax to make it easier to bring
the feeders into your shack.

A compromise is to use ladderline from the antenna to the building and then
use a W2DU 1:1 bead balun on coax to make the transition from balanced line
to unbalanced line and then run the single coax into the building to your
tuner, etc. That is how I operate three different antennas here with good
results.

I hope this is of some help, Gary. Please email directly if you have any
more questions.

72/73/oo, George W5YR - the Yellow Rose of Texas         
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe   
Amateur Radio W5YR, in the 56th year and it just keeps getting better!
QRP-L 1373 NETXQRP 6 SOC 262 COG 8 FPQRP 404 TEN-X 11771
Icom IC-756PRO #02121  Kachina #91900556  IC-765 #02437

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Gary Lee wrote:
> 
> I had asked a question prevoiusly about the spencer dipole fed with twin
> rg-11 as a balanced shielded feedline.
> 
> I have since read all the responses, and asked everyone I know.  Can't find
> the referenced cq article from 1989, and haven't found a satisfactory
> explanation on line.
> 
> The consensus seemed to be that this method of feeding could be lossy.
> Could some kind soul please explain pros and cons without the use of
> pictures as I am totally blind.
> 
> Tried the arrl antenna book, but the pictures were not well described on my
> cassette copy.  This, it appears, would be a difficult job.
> 
> Thanks for any  help.