Ian, GM3SEK wrote:
"Can you describe that please?"

Gladly.

For low loss at 100 KW, you use large cable and wide spacings at 600
ohms. It may have been more economical to use more conductors but for
simplicity we stuck with a 2-wire balanced feed system. We had at that
particular time and location the largest congregation of high-powered
shortwave transmitters and directional antennas in the world. We
installed a crossbar switching system so that almost any transmitter
could access any antenna. We were on the air with most transmitters
operating nearly 24 hours a day, but switching antennas several times a
day according to our announced program schedule to accommodate
anticipated propagations to the target areas served.

Ed Laport as Chief Engineer of RCA International had as much experience
as anyone with commercial shortwave radio, so we relied upon him for
information and weren`t disappointed.

On page 396 of "Radio Antenna Engineering", Ed illustrates a corner made
using two transmission lines. He shows a single pole with two crossarms,
one above the other and making the horizontal angle required for the
intersection. He terminates the lines one on each crossarm. Jumpers are
used to interconnect the two lines.

Our line cables were akin to welding cable. We joined them with sleeves
and fittings attached with a hydraulic press (Nicropress). With wide
spacing the lines are tolerant of bumps and don`t tend to flashover.

Ed gives a graph of the value of the ratio of line spacing to cable
radius versus Zo. For 600 ohms the ratio is about 150.

Best regards, Richard Harrison, KB5WZI