On Mon, 03 Nov 2008 12:05:07 +0100, Thomas Herrmann wrote:
>Are there available any good experiences with 1:4 Guanella
>(current) balun, consisting of 2 separated coax air coils (1:1
>baluns) on TopBand with high power ?
The higher power rated DX Engineering 1:4 baluns are two
ferrite core (Fair-Rite #31) wired in series on the 4 side and
parallel on the 1 side. This sort of design is superior to air
core, because it provides significantly more common mode
isolation. The DXE unit I own (and have measured) is rated for
much more than 1.5kW. It sells for about U$130. You can see
photos of this choke in the Power Point on Coaxial chokes on my
website
http://audiosystemsgroup.com/publish
Common mode choking could be improved even more by adding a
coaxial choke in series on the low-Z side, using the techniques
described in
http://audiosystemsgroup.com/RFI-Ham.pdf
For 160M, it is quite important that #31 Fair-Rite material be
used for the cores.
The more important question, however, is antenna and feedline
balance. Although the line itself might have physically
balanced construction, it can carry significant common mode
current because the antenna is unbalanced by its surroundings.
This would make the antenna noisier on receive. The solution is
a good choke at the feedpoint, but it's tough to do that and
handle high power unless the choke is wound with coax on #31
ferrite cores. Again, study those references on my website
about this.
73,
Jim Brown K9YC
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