On 9/15/2012 5:26 PM, Scott Yost wrote:
Is Isobar still considered a decent product for RFI reduction or has it been
eclipsed by some other manufacturer? The Isobar website seems thin on specs
for noise suppresion data. Interested in specs especially at LF.
I can't comment about RF filtering, but it's an MOV box, which is BAD
NEWS on a branch circuit. Also, none of the commercial line filters do
anything to kill common mode current on the AC cable (which is on all
three conductors, INCLUDING THE GREEN WIRE), and the green wire must, by
law, go through the box without putting anything in line with it.
That's bad news, because much (most?) RF trash on house wiring is COMMON
MODE.
The most effective common mode filter I know of is to simply wind lots
of turns around a #31 core. I can get at least 14 turns of most common
IEC power cables through a 1.4-in i.d. #31 core without removing a plug.
14 turns is quite effective down to at least 80M, and is still good on
160M. More turns is better if you need to go lower, or you could wind
turns through two cores in a stack. Two or more cores in a stack also
helps if you're using larger diameter cable and can't fit as many
turns. As a rule of thumb, 10 turns with two cores is roughly
equivalent to 12 turns through one core. That's because inductance is
roughly proportional to the length of the path through the core
material, but proportional to the SQUARE of the number of turns, and
capacitance is proportional to turns.
73, Jim K9YC.
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