[RFI] Adding a shield to the utility service lines?

Dale svetanoff at earthlink.net
Sat Dec 7 11:04:15 EST 2013


I have been following your thread with interest.  The various comments posted have offered a lot of good suggestions and safety issues.  Here is the bottom line:

1.  For actual RFI that is carried into your building via the power lines, I agree with K9YC that most problems are common mode and would require filtering of ALL 3 power leads: 2 Hots and the Neutral.  There might be some differential spikes or transient surges, but the filters would clean up the fast (short duration) ones and a mains surge suppressor, installed at the main power panel, would handle the longer duration surges.

2.  There is such a thing as a 3-line power filter.  It is called a "facility filter" in the trade and is used by the military and others who need very "clean" power.  You would need either a 100 amp or 200 amp model, depending upon your power requirements.  They are made by a number of manufacturers, but here is the catch: Co$t!  Unless you can find one on the military or industrial surplus market, a new 3-line power filter will be somewhere in the $5k to $10k category, and perhaps more.  I might add that having an absolutely solid ground is essential for proper filter function, as the filters work by a combination of reflection of RFI and by-passing to ground of RFI currents.  Without a very solid ground, the noise will just continue to propagate around via the grounding wires.  I might also add that the filter would be installed at your house, NOT out on the power pole.  Thus, you could still have radiating power wires.  

I strongly recommend installation of a whole-house surge arrestor at the main power panel as protection against surges and lightning-induced line spikes.  As for your RFI problems, nothing beats tracking down the source(s) and trying to get them addressed.  As has been posted here many times, if you can ID the source and it is the power company's equipment, you have a fair chance of getting the problem resolved.  If the source(s) is/are caused by privately owned user equipment, you then have to face the problem of either living with the RFI or contacting the owner of the offending equipment and trying to work out a solution.  In either case, you need to get active and locate the sources.

73, Dale


-----Original Message-----
>From: Aaron Kreider <aaron at campusactivism.org>
>Sent: Dec 6, 2013 6:25 PM
>To: rfi at contesting.com
>Subject: Re: [RFI] Adding a shield to the utility service lines?
>Thanks for you advice.
>On 12/5/2013 12:45 AM, Jim Brown wrote:
>> On 12/4/2013 9:33 PM, Aaron Kreider wrote:
>>> Another crazy option
>> Yes, it is.  Shielding addresses differential mode RFI, and most trash 
>> on power lines is a common mode signal and radiates just like any 
>> other antenna. Although I tried a bunch of big clamp-ons on a twisted 
>> triad power feed back in Chicago, it was long before I understood how 
>> ferrite chokes work, and I'm now nearly convinced that it was a bad 
>> idea because a string of beads is inductive.
>> Even if you could shield that line (it belongs to the power company, 
>> so it's not a good idea), the common mode current would flow on that 
>> shield, and you would still need to choke it to prevent it from 
>> radiating.
>> 73, Jim K9YC
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