On Sat, 2007-12-08 at 10:21 -0800, Jim Brown K9YC wrote:
> On Sat, 08 Dec 2007 08:18:02 -0500, Bwana Bob wrote:
> >hanks, Bob
> >Yes, my coax-fed 80m dipole only works on 80m and its odd harmonics.
> >That's why I'm planning to switch to balanced feed. After reading the
> >material on W2DU, Walt Maxwell' site, I'm going to try a ferrite bead
> >current balun with a short run of coax to the tuner.
Using an ultimate transmatch circuit (split dual 140 pf input C,
switched coil, variable 150 pf on the antenna side) I'm successfully
tuning my 80 meter inverted V, no fan, from 80 through 10 meters.
Including 60, 30, 17, and 12 meters. The feed line is about 60 feet of
RG-142, essentially RG-58 with teflon insulation and silver plated
conductors. It seems to weather well. I'm sure the radiation pattern is
poor on some bands, but it hears and sometimes gets out. I'm not using a
> Several suggestions. First, consider a FAN dipole, which is very easy to
> build and works really well with coax. My 80/40 fans work well on 30M and
> 17M too.
> Second, study my material on coax chokes (current baluns). It's a 25-year
> later expansion of Walt Maxwell's work using toroidal cores to wind multi-
> turn chokes that provide FAR better choking of the feedline. This has the
> advantage of significantly reducing noise picked up on the feedline as
> compared to Walt's "string of beads" chokes. BTW -- Walt has read my work
> and says he likes it.
> To reduce the feedline noise, the choke MUST be at the antenna feedpoint.
> You can't wind a current choke with twinlead -- it MUST be wound with coax.
> You COULD use a small section of coax with that choke, then transition to
> twinlead if you wanted to. That would work.
> Another point re: an earlier post in this thread. It has been shown (in an
> excellent piece of research published in one of the ARRL Antenna
> Anthologies) that conventional window line is rather lossy (worse than coax)
> when it is wet. Cutting the windows as was described reduces that loss.
> Jim Brown K9YC
73, Jerry, K0CQ
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