On 2/7/2020 1:11 PM, krgoodwin@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
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