[RFI] Fixed my S9 furnace RFI

[ac2ev]

I found recently that my furnace was creating terrible RFI on 40m (and 20m too). I could only hear the strongest stations and could barely see them on my panadapter. 

After much reading I started investigating to see ways to mitigate it. I tried ferrites at first on the likeliest culprits and even tried a line filter on the incoming line. Some more investigating and emails to the various component manufacturers led me to discover the culprit. 

It turns out that my Rheem contour high efficiency furnace has a 3-phase draft inducer motor. Rheem has a control board that creates a pseudo 3-phase signal from the 110VAC single phase feed. 

Now how to fix it? Well it turns out the simplest solution was the best. I
Replaced the four wires that went from the controller board to the motor with a single 4-conductor shielded wire. The shield was connected to ground on both ends (this worked best) I'm happy to say my RFI is completely gone. I do have a 3-phase  line filter just in case.

Good engineering practices were followed.

I left the factory wires abandoned in place, should I need to plug them back in for some reason. I also ensured that the wire I used met the same rating as the original with regards to voltage, AWG, temperature, etc. I also made sure to use a cable gland so as to both prevent cable strain and to maintain the integrity of the isolation between the combustion and blower.  

73
AC2EV - Don