[RFI] choking the service line

Jim Brown jim at audiosystemsgroup.com
Mon Sep 9 17:08:24 EDT 2013

On 9/9/2013 1:49 PM, Aaron Kreider wrote:
> How much attenuation can I get for 2 mhz to 6 mhz, per choke, by using 
> monster chokes (material 31, 1 inch ID) on the service line?
> What is the regular impedance of the service line at these frequencies?

There's no good answer to this -- what I was hoping to do when I tried 
that was to reduce common mode radiation by the service line acting as 
an antenna, and radiating to my antenna directly above and parallel to 
it.  It all depends on the length of that cable as a fraction of a 
wavelength at every frequency of interest. Not only that, but if the 
length of the cable causes it to be inductive at some frequnecy(ies), 
the inductive component of the cores will cancel the inductive reactance 
and the current could increase. :)

> From page 31 (Understanding and solving RF...), it looks like I'd get 
> around 32 ohms resistant at 2 mhz and 68 ohms at 6 mhz. 

When I tried this in Chicago, I had no good way to A/B test it, and I 
was never convinced that the choke did anything useful.  But I did want 
to show that it was perfectly safe to use chokes on feeders carrying 
large currents so long as both sides of the path passed through the core.

73, Jim K9YC

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