[Elecraft] A Correction About Feedlines...

[Ron D'Eau Claire]

A while back I made a post about using K-rigs with their ATU's with open
wire vs. coaxial feedlines.

I stated that open wire feedlines were more efficient than coaxial cables at
high SWR's because the dielectric losses were higher in coaxial lines.

A couple of readers observed that they thought it was the resistive losses,
not dielectric losses, that were the cause. I replied quoting design
handbooks, principally ARRL Antenna books written 20 years ago, as saying
the losses were caused mostly by the dielectric, or insulation, used in the
feedlines.

After a number of off-reflector exchanges with readers, it is clear that the
sources I was quoting are no longer claiming that to be true. In particular,
the more recent ARRL antenna books say. "Dielectric losses are generally
negligible below UHF frequencies."

What has changed? Perhaps insulators are better these days. Perhaps a
long-held opinion was overturned by better test data. I don't know.

My thanks to those who questioned my statement. You started an interesting
dialogue exploring the subject and looking for references.

In particular, thanks to Lou, W7DZN who found the latest quote in  new ARRL
book, "Simple and Fun Antennas for Hams." In the section on transmission
lines.

What remains true is that well-constructed open wire feedlines are still
more efficient than coaxial lines, and when the SWR's get up into the range
of 10:1 or 20:1 and more, the superiority of open wire lines is substantial.

Ron AC7AC
K2 # 1289