[RFI] choking the service line

Aaron Kreider aaron at campusactivism.org
Tue Sep 10 19:17:03 EDT 2013

Has anyone ever tried covering the service line with tin foil, foil 
tape, or conduit?  That'd probably provide the best attenuation other 
than burying it.

Does anyone make a snap-on conduit?

If you had to guess, what range of impedances would a service line like 
have at 2-6 mhz?  Could it easily be as high as 500 or more ohms?    I 
think my power line/service line might be resonating at 2.3 mhz (and 
possibly also around 3.2 mhz).  Presumably where it resonates, it'd have 
the lowest impedance and best chances of ferrite suppression.


On 9/9/2013 5:08 PM, Jim Brown wrote:
> 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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