I am not sure exactly what you mean by a "a wire antenna, 15 feet
above a flat metal roofed building, (it a NVIS antenna), and resonant
at 6.2 MHz".

I assume you mean a centre fed dipole that is an electrical half wave
at 6.2MHz.


Yes. My appologies for leaving out a critical description. Its a
wire centerfed halfwave antenna, 15 feet above a flat metal roof, and
resonant at 6.2 MHz.

The people who installed it expected the tuner in the FT900 radio to
handle the matching. I explained that the tuner was never intended to
match an antenna that would be so far off resonance. To compound
matters, they are using at least 100 feet of 50 ohm coax... mostly RG-
8, I think.



The efficiency of the radiator component can be estimated from an NEC
model, it is probably very high and not the real issue.


Well, in this case, it IS a necessary issue. I wish to present the
probably actual feedpoint SWR to these people so they will realize how
far beyond tolerance they are trying to use that built in tuner. That is
why I was asking for SWR estimates for 3.95MHz, 7.2MHz, and 5.4MHz.

I intend to propose going to a resonant antenna, and use traps or
multiple dipoles to present a near 50ohm feedpoint to the coax and tuner
for those three frequencies of operation.


... so.... if anyone could run those figures, I'd sure appreciate it.


Ed

PS: Thanks for the info, though, Owen.