On Wed, 11 Nov 2009 09:29:51 -0600, K4SAV wrote:
>The choke balun will work (depending on how much impedance you
really
>need). There are some advantages to using a ferrite core,
There is a MAJOR advantage to using a ferrite core -- it makes the
choke RESISTIVE rather than inductive. A feedline shorter than a
quarter wave looks capacitive in the common mode circuit. Adding an
inductor in series (the coil of coax without the ferrite) tunes out
that capacitance, which reduces the impedance and INCREASE THE
CURRENT.
A ferrite choke with a sufficient number of turns and cores can add
5,000 ohms of resistive impedance to the common mode circuit that
can't be cancelled by the length of the line.
> but obtaining the core(s) is sometimes a problem.
Naw, you just buy them (but not from the vendors who advertise in QST
and sell at rip-off prices). See the list of Fair-Rite part numbers
(the actual manufacturer) and list of vendors on the Fair-Rite
website and in my tutorial, previously cited. The Cookbook lists the
number of cores and turns needed for each band.
Over a period of about five years, I've helped organize group
purchase of cores for nearly a dozen ham clubs. These parts are very
reasonably priced if you buy them right.
73,
Jim Brown K9YC
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160 meters is a serious band, it should be treated with respect. - TF4M
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