[Antennas] twin coax as shielded balanced line

[Harvey&Bessie]

Of course there is nothing wrong with feeding a balanced load with twin
co-ax as a balanced line. But it would not match an thing but an antenna
with a center impedance of 250 to 300 ohms. If you have such an antenna,
fine. But with the ordinary dipole (center impedance about 50 to 80
ohms) there will be a mismatch, causing high SWR and coax has higher
loss with high
SWR. So the reason you have been told it is a lossy way to feed a
dipole. Note: many people are under the impression that a "tuner" gets
rid of SWR on the line. This, of course is not true. The tuner,
transmatch or whatever, only allows the transmitter to "see" the load it
is designed for. The SWR on the line is not affected by the tuning
device.
W4TG/Harvey