[Elecraft] Elecraft] RFI on K3s

[Jim Brown]

On Tue,6/21/2016 9:22 AM, brian wrote:
> Nothing has been mentioned on what had been standard practice years ago.
>
> That is installing a good RFI filter on the mains right at the station.
> These filter can knock things down 40 dB in both directions. 


The reason nothing has been mentioned about it is that it doesn't do 
much to solve RFI problems. That's because MOST RF noise is coupled by 
common mode radiation from systems and common mode reception to systems, 
not by differential mode, and these filters do NOTHING to kill common 
mode current.

The data sheets for commercial filters quote numbers for "common mode" 
suppression, but what the power industry calls common mode is the 
voltage between neutral and the green wire. That's NOT what the rest of 
the world calls common mode, which is a longitudinal current ALONG the 
cable pair, and which causes the cable to radiate (and receive)  like 
any other antenna.

More than five years ago, I bought some good commercial power line 
filters and mounted them in electrical boxes to put in line with the 
output of the Honda 2000i generators that we use for CQP county 
expeditions and Field Day. Those filters did NOTHING to suppress the 
noise. What DID work was a common mode choke formed by winding 4-5 turns 
of the power cable through 5 #31 cores.

73, Jim K9YC