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

Jim Brown jim at audiosystemsgroup.com
Sat Aug 22 21:16:34 PDT 2009

On Sat, 22 Aug 2009 20:48:54 -0500 (CDT), Christopher E. Brown wrote:

> Backed up right to the 
>house I get the elevated noise floor across the band (mainly looking at 
>20M here, because it has the least radiated noise outside of a few known 
>sources but wideband noise is there everywhere 20M and down).  Pull out 10 
>- 50 feet and (on the short whip) it goes away.  Back into a neighbors 
>driveway 4 houses down and get close to the house and same effect (though 
>it was harder to tell as this also brought be close to their home 

It sure sounds like you've done all the power system right. What's your soil 
like? Good ground? Poor ground?  

Here's the connundrum. If the noise source is outside the house and it's 
return path is earth (likely it's common mode), why is the noise level 
rising on the house side of that ground? Logic suggests either 1) there's a 
noise source on the house side of the ground or 2) it isn't a very good 
ground; or 3) there's another ground on one or more branch circuits, which 
provides a current path for common mode current. I'm guessing you've checked 
that. :) 

One possibility is that the ground is simply placing a voltage minima on the 
line (long wire antenna) and as you come into the house the voltage is 
rising. That suggests CAPACITIVE (E-field) coupling from the power line 
inside your home to your antennas. You might get a clue by taking a talkie 
with HF RX and a duck antenna and probe along the lines to look for peaks 
and dips. 

Question. Is it practical to put your wiring in EMT? Probably not. :)  

Another observation. I was chasing noise on 160M and took the HF RX in my 
THF6A talkie for a walk around the neighborhood. One thing I did was to 
couple the talkie's mag antenna to every wire I could find that was on a 
wooden power pole (feeders, grounds). Sometimes I would hear noise. 
Sometimes I would hear 160M signals, coupled from that downlead to my 
talkie. One I specifically remember because he's about 1,000 miles from me 
and he was loud, was W7LR. So in that case, the talkie's loop antenna WAS 
inductively coupling to that power pole's downlead. 


Jim K9YC

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