These are not "excellent" 1:1 current baluns below about 75 MHz. Below
that range, they are a lousy common mode choke, because they are
inductive. Inductive chokes resonate with a line that is capacitive, so
they actually increase the current. A line shorter than a quarter wave is
capacitive; so is a line between a half wave and 3/4 wave. And so on.
That's why we want a choke that is highly resistive -- the resistive
component always reduces common mode current, which is the objective of a
common mode choke (the so-called "current balun.")
You may be confused, or I am. He asked about 31 mix beads:
<<<<
Hi Folks;
Thanks a bunch, to all those who responded with source possibilities for 31
mix toroids ! I will add a note here, after I actually make a purchase to
designate the lucky victim of my small purchase.
73 Dean W5PJR
31 materials has a Q of about 1 on 80 meters. This means a good part of the
impedance is resistive.
While I don't beads are a good choice with large coax, only one pass can be
made through the window with normal types of high power coax, I don't think
the material itself is all that bad.
Also, attenuation has as much to do with grounding and wise engineering of
common mode shunt impedances as it does choke impedance. Choke material is
almost always a compromise between heat and Q at high power. For receiving,
lossy common mode choke materials always work. Not so for transmitting. One
size will never come close to fitting all.
73 Tom
All good topband ops know how to put up a beverage at night.
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Topband Reflector
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