"Meindert Sprang" wrote in message
...
"Jack Painter" wrote in message
news:SR2tc.76990$pJ1.75446@lakeread02...

1. RF feedline from ATU to antenna.

This should be coaxial cable with dialectric and shielding designed for
RF.

Imagine what 2 meters of coax with a capacity of 200pF ( a "load" of about
200 ohms at 4 MHz) does to a high impedance (several kOhms at 4MHz)
antenna
connection: right... almost short circuit it to ground.
NEVER use coax between the ATU and the antenna.

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. It appears (to me) no
different that the ungrounded dipole that I feed with coax from my land
station tuners. I have also fed a longwire with that same tuner/coax
combnation, however the longwire was a grounded antenna, and not simlar to a
insulated backstay of a sailboat.

Best regards,

Jack Painter
Virginia Beach,VA

"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