On Fri,8/21/2015 8:31 AM, Greg Troxel wrote:
Have you tested/evaluated the RadioWorks T-4G+ line isolator, or the
similar things from MFJ?
No. Looking at the photo and lack of specs, I wouldn't expect them to
work very well.
I know you recommend many turns around
specific mixes, but I'm curious what the shield impedance is on these.
See my measured data, and method of measurement. k9yc.com/RFI-Ham.pdf
The problem with all-band non-resonant antennas fed with open wire line
is that it is not practical to choke the feedline effectively. Dean
Straw, N6BV (retired ARRL Antenna Book editor), showed this quite
clearly at the Pacificon Antenna Forum several years ago. To be
effective, the choke must be at the antenna feedpoint, the choke must
have a very high RESISTIVE choking Z. The only practical chokes I know
of are low impedance lines -- either coax or a short section of parallel
wires wound on a toroid.
Close-spaced enameled wire yields 50 ohms, close-spaced THHN (house
wire) about 90 ohms. Jerry Sevick published this work 20 years ago, and
I've confirmed it in my own lab. Those "all-band wonders" operate with
very high VSWR on most (all?) bands, and the resulting mismatch fries
any choke that might otherwise be useful.
73, Jim K9YC
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