It sounds like you have an older marine transceiver with built in
antenna coupler, which is not uncommon. A tech would install the radio
and match the whip (non resonant) and random wire feeder by choosing
coil taps and tweeking a cap for each channel. The channel selector will
now select the correct coil/cap to match properly the antenna. If the
radio or antenna is moved you must retune the network to match the
antenna again. If this is the case here you would have to bypass the
coupler section and remote it to make the radio happy feeding coaxial
cable, probably a big project.
Mike


John - G0WPA wrote:
Hi there,

I have a marine MF (1 to 7 Mhz) transmitter with only an antenna "screw
terminal" for a long wire connection on the back of the set, rather than an
SO239 or N type, and the set itself being grounded with copper sheet to a
decent earth. My problem is, I need to feed an MF whip on the roof, some 50
feet away, through the building, offices etc, and dont really want the EMC and
Health and Safety problems that would arise from 400W PEP happily radiating
indoors with the recommended wire lead-in. So I'll need to use a feeder. I have
decent low-loss coax (LMR type) but how do I couple it to the set? ..and to the
whip (just a long-ish wire in fiberglass) at the other end. Im thinking an
unbalanced to unbalanced transformer at both ends of the coax should do it,
with both the tower and the set in the workshop grounded but the coax outer
isolated. I have toroids that will do it, but how should I wind them? Im
thinking MF ununs could be made by winding 10 or 12 turns of coax on suitable
toroids. Is this reasonable or am I way off.

ALL suggestions, even those calling me a muppet , will be very gratefully
received.

Thanks, John G0WPA.