[RFI] How much RF does your power company deliver along with the AC?

Jim Brown jim at audiosystemsgroup.com
Sun Aug 23 11:08:17 PDT 2009

On Sun, 23 Aug 2009 03:09:31 -0500 (CDT), Christopher E. Brown wrote:

>Repeated the same but with 10 turns through a 2.4in toroid in the middle 
>of the cord.

>12 to 18 inches past the choke and I have to place the loop against the 
>cable jacket to detect the noise and even then it is weaker.

OK, try this. Make that extension cord 100 ft, add the choke at the point where 
it plugs into an outlet, and repeat that test, going all the way to the end of 
the cord. Try this with chokes tuned to the frequency range where you're most 
concerned. For most power cables, the data for RG8 or RG8X chokes should 
approximately account for the capacitance associated with wire size. 

It that still cools off the longer cable, a similar choke on one or more branch 
circuits in the panel should also be effective. For the test, your electrician 
may have to leave the panel open, and he'll need to temporarily patch the choke 
wound with 2 or three twisted conductors in series with the branch circuit. If 
that works, he could add a junction box outside the panel to hold filters for 
branch circuits. 

>From a common mode point of view, it's a sort of voltage and current divider. 
There's some series source impedance, probably fairly low (but not necessarily) 
and probably complex (that is, at least R +/- jX), the impedance to earth of 
your ground electrode(s), and then the branch circuit wiring. When we add the 
choke, we cause less of the current to flow on the branch circuit and more of 
it to go to the ground electrodes. 


Jim K9YC

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