[RFI] Multi-Stage High Efficiency Air Conditioner Units

[Jim Brown]

On 2/7/2020 1:11 PM, krgoodwin at comcast.net wrote:
> The culprit was the thermostat line
> (4-conductor) where installing an RF filter (LC circuit) on each of the four
> conductors in addition to some ferrites on the line easily solved the
> problem.  Next re-install I will put in a shielded multi-conductor
> thermostat control line which was my baseline for the house LAN (shielded
> ethernet line).  Shielded cat XX (ethernet) line costs more but I think the
> cost is worth it since my tower/beam is right next to the house

Thanks to its high twist ratios, UTP CAT5/6/7 cable provides excellent 
rejection of differential mode coupling. In my experience, most coupling 
at HF and MF is common mode, by simple antenna action combined with 
inadequate CMRR in the victim. Multiple turns wound through a #31 
Fair-Rite clamp-on, or more turns through a #31 2.4-in  toroid will make 
a big dent in common mode coupling. The choke should be very close to 
the AC unit. Cable shielding can be effective ONLY if the shield is 
properly terminated to the shielding enclosure at the victim.

 > In the front end of any good graduate level antenna text resides the
 > Theorem of Reciprocity:  "A good emitter is a good receiver".

Gee, I encountered that principle as early as my junior year in EE, and 
having been licensed for six years by then, I had probably learned it 
earlier through study of ARRL publications. In EE, probably in my 
circuit analysis course when we studied filters and peaking networks.

73, Jim K9YC