> Gary, was your 140 ohm WD-1A made from .0393 (1mm) diameter wires, spaced
> .118 center-to-center? My math says that should be a little over 140 ohms.
>
> But the stuff I was talking about was a different diameter and spacing
> (.033 diameter and .0685 center-to-center spacing.) The same math says
> it's
> ~115 ohms, but I had no way of measuring a piece less than a foot long.
Since the field extends outside the dielectric, all bets are off. Even if
the strongest area of electric field is between the conductors, we really
don't know the percentages of what dielectric are involved.
That's why a measurement is best. Tuning between a frequency where length is
and odd 1/4 wave and even 1/4 wave electrical and adjusting for most
constant SWR would hit pretty close.
I think to make any meaningful tests, I'd use either 50 feet or 100 feet of
line. Anyone with a movable power meter, antenna tuner, and transmitter, as
well as an antenna analyzer, could probably measure loss and impedance as
well as any VNA.
73 Tom
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