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

Jim Brown jim at audiosystemsgroup.com
Sat Aug 22 09:34:56 PDT 2009

On Fri, 21 Aug 2009 21:44:29 -0500 (CDT), Christopher E. Brown wrote:

>Perhaps I did not state things as clearly as they could have been, but you 
>may want to re-read my original message.

Something else that comes to mind based on the symptoms is the grounding of 
the power line and your shack. The ideal is a very low impedance (very 
short) bond between the power system ground electrodes and your ham station 
ground electrodes. If there is noise on the power system and it is flowing 
to ground, you want it going to ground by the shortest path, one having a 
very low impedance, and one that radiates the least. You don't want it to 
have to go through your building wiring to your shack ground.  

One thing I did in Chicago to attack a similar high noise level was to put a 
string of #31 "big clamp-ons" on the 120V-0-120V twisted triplet overhead 
service to the building that ran more or less under my dipoles and more or 
less parallel to them. What I was trying to kill was the radiation from the 
power line into the dipole. One limitation of this approach is that at some 
frequency, the power line, with a high inductance at one end (my choke) 
becomes a resonant end fed antenna. :)  

It seemed to help a bit on 30 and 40M, but there was a lot of noise that 
came straight from my neighbors' houses (battery chargers, power supplies, 
etc.). I had about seven of them in the string, and I think more might have 
been better, but I used what I had. About the time I would have added more, 
I found this new QTH in CA and started moving. :)

The "big clamp-ons" are the 1-inch i.d. parts documented in my RFI tutorial. 
A string of these is far from being an ideal RF choke for HF, because it 
will look inductive, not resistive. 


Jim K9YC

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