"Jack Painter" wrote in message
newsxstc.52$9h.43@lakeread02...

Hi Meindert, I don't understand your reasoning there, sorry. And Doug
too,
who referenced a steel ship, which is my reference as well. I have seen
hardline (still 50ohm coax) in shipboard installations using the same
Sunair
ATU that I use, connected to the wire HF antennas.

A backstay antenna is relatively short compared to the wavelength. It
therefore has a high impedance. To match it to the 50 ohm of the
transceiver, the impedance has to be transformed by an L-circuit with the
capacitance at the low impedant side to ground and the inductance from the
low impedance "hot" side to the antenna. If you would use coax at the high
impedant antenna side, you get a terrible mismatch. The capacitance of this
pice of coax adds to the L circuit at the wrong side, effectively giving you
a PI circuit which is unable to match the high impedant backstay to the 50
ohms of the transceiver.

It appears (to me) no
different that the ungrounded dipole that I feed with coax from my land
station tuners.

Theoretically no. But your land dipole is probably much longer than a
backstay and therefore has a lower impedance. By the way, does your coax
connect directly to the dipole or do you have a balun (with a possible
impedance transformation wich makes the coax have less influence)?

Meindert