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.
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 signficantly 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.
http://audiosystemsgroup.com/RFI-Ham.pdf
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.
73,
Jim Brown K9YC
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