> For example, when used in the multiband doublet application 200ft of
> Wireman 553 has about 2.6dB of loss at 28MHz. When wet, that figure
> rises to 9.3dB, based on the work of Wes Stewart N7WS.
And the reason I've been using homebrewed open 600-ohm line -- using the 276
log formula :-)
The line uses E.F. Johnson glazed ceramic spreaders spaced every 18-inches.
Total of roughly 50 ft. of line between a 130 ft flat-top dipole to a
ground-mounted motorized symmetrical balanced tuner. When QRT, the
balanced line is automatically disconnected from the tuner with a pair of
Jennings vacuum switches to form a quasi "knife switch." LMR-400 between
the ATU and shack. The open feeder length represents a reasonable end-Z
compromise on all bands from 80m-10m and remains under 1,000 ohms and over
50 ohms at the tuner terminals at all times. 50-ohm VSWR never changes,
wet or dry. Next time the line comes down, a re-application of Rain-X is
needed on the glazing. ATU details on my QRZ.com page.
Been tempted to replace the Johnson spreaders with Delrin but I doubt
there's much difference in total dielectric loss with such a short run of
line.
http://www.73cnc.com/73cnc/laddersnap.html
Paul, W9AC
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