I must admit to all of you that this is giving me a headache- but I am
enjoying it. Antennas and their support systems(feed lines/tuners etc.) are
my favorite part of this hobby. I never cease to be amazed that I can at
times communicate with hams on the other side of the world with 100 watts
and a piece of wire 30 feet above my home. I wish I was more intelligent and
higher in education- but it is what it is. I have had success with a 17m
extended double zep fed with 400ohm ladder line and a cheap balanced
tuner(mfj). It is showing fatigue from years of weather so I will pull it
down and start over. Feed line length is always a puzzle and reactance seems
to be more of a challenge for my transmatch than high resistance.
300 ohm ladder is appealing as it is more stealthy but the homemade 600 ohm
is very interesting and would be a fun project also. I think I will order a
package of 73cnc spreaders and give it a go. I would like to make a
transmatch and wonder if anyone could recommend a circuit/plan that would
suit me and that I may be able to find parts for.
On Sun, Jan 9, 2011 at 1:31 PM, Paul Christensen <email@example.com> wrote:
> > 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
> 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
> Paul, W9AC
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