[RFI] RFI Digest, Vol 203, Issue 49

[Jim Brown]

On 12/20/2019 1:45 PM, Dennis Monticelli wrote:
> FYI. We have a bad HF noise problem at the California Historical Radio
> Society that stems from numerous high-mounted LED fixtures (not FEIT) in
> which there is a third wire from fixture all the way to the sub-panel.  The
> problem with third wires is that by the time they thread their way through
> the building and find earth ground, they do not represent an RF ground.

There is no such thing as "RF Ground." The earth is not a sump into 
which noise is poured. Most RF noise not radiated directly by a source 
is conducted onto external wiring as a common mode signal. And thanks to 
improper termination of the "green wire," common mode current is usually 
ON the Green Wire!

In general, the FIRST thing we should do to kill noise is to add a 
suitable common mode choke to every cable connected to the noise source, 
using winding guidelines in http://k9yc.com/KillingReceiveNoise.pdf for 
smaller cables and http://k9yc.com/2018Cookbook.pdf for larger cables.

73, Jim K9YC