I wanted to report my experience for the record.
I replaced an old, failed heat pump/air conditioner system. I specifically
asked for a system without variable speed motors because I had read that
they're trouble. A non-variable-speed Trane XR15 (that seems to be the
marketing model number) system was installed. Specifically, the outside unit
is a model 4TWR5024E, and the inside air handler unit (in the attic) is a
model 2/4TEH3F24B1000A.
The old system used regular old AC induction motors, and it was completely
silent from an RFI perspective.
This new Trane system is not silent. The problem is the air handler unit
mounted in the attic. Its motor is an ECM type and, although not variable
speed, it generates considerable RF. It's 20 to 50 feet away from my various
antennas, and unmodified it produces groups of spurs (a bunch of closely
spaced carriers; each bunch is about 30 kHz apart) from 17 through 50 MHz.
The signal strength varies from S3 to S9.
I put a few snap-on ferrites on the wires coming out of the motor, and the
interference was reduced substantially (maybe S3 at worst; most other
frequencies barely audible). I may go back later to try to fine tune the
treatment for better results, but when I did the work it was really, really
hot in the attic so I got in and out as quickly as possible.
73,
John, W1JA
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