[RFI] rf current meter and ferrites
jim at audiosystemsgroup.com
Tue Sep 22 13:52:07 PDT 2009
On Tue, 22 Sep 2009 23:06:40 +0300, Kostas Stamatis wrote:
> I thought
>tha the difference is between rig and ferrites.
It's a bit more complicated than that. Study my tutorial on ferrites
The short answer is that the cable you're putting the ferrite choke
onto is an antenna, and the ferrite choke is a very low Q parallel
resonant circuit that modifies the behaviour of that antenna. The
characteristics of the resonant circuit, including its resonant
frequency, are set by mainly by varying the number of turns and the
material, and secondarily by varying the winding style. Near
resonance, the choke looks like a high resistive impedance, so it
divides the wire into two pieces. The part of the wire between the
noise source and the choke radiates, the rest of the wire does not.
Far from resonance (more than an octave or two), the choke looks
either inductive (below resonance) or capacitive (above resonance),
and can resonate with the cable to make it a better antenna.
Jim Brown K9YC
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