Dave wrote:
Mark wrote:
modelman wrote:

Several months ago I had a high efficiency Trane XV90 natural gas
furnace and heat pump installed. Since the weather has recently been
cold enough for the gas furnace to provide heat, I have been
experiencing severe radio interference. The interference wipes out AM
broadcast reception throughout my house. I also see snow on a TV
connected to an external antenna.

The radio noise occurs as soon as the draft inducer motor starts up;
the pitch of the interference is related to the motor speed. The draft
inducer motor is a dc motor driven by a PWM controller on the main
circuit board. ... SNIPPED ...

DC motors are notorious noise generators. Those of us who used to be mobile when
6 VDC was the value of a car battery, and alternators did not exist, will attest
to the facts of generator [DC motor] noise.

A DC motor uses brushes to contact windings within the motor. As the motor turns
the brushes continually make and break current in the rotating armature
[inductance]. This making and breaking creates a very wide HF and lower VHF
noise spectrum. [Lots of sparks].

The solution, in the olden days, was a coaxial capacitor mounted directly to the
frame of the motor with the DC power running through the capacitor. I recall the
capacitor was about 1 inch in diameter and 2 inches long. Sprague made such a
critter.

Hope this history helps.

/s/ DD, W1MCE

I'm pretty sure these motors don't have brushes and are electronically
commutated and the electronics are causing the EMI...
Mark