[RFI] Weather related RFI

Jeff Stevens jeff at mossycup.com
Mon Sep 23 14:07:04 EDT 2013

This is just a total shot in the dark but do they have an air source
heat pump which was installed within the last few years?  Sometimes
these are called ductless AC units.  The newer models use PWM to drive
the compressor.  The variable speed drive which PWM allows makes the
units much more efficient (they can run more or less continuously
instead of all on or all off) but PWM is, of course, full of
harmonics.  The unit I had recently installed is below the noise floor
at my antennas but I can see poorly filtered models being a real
problem for radio amateurs.  If they had an air source heat pump
installed, you should see the compressor on the exterior of the house.
 It will look something like this:

If you live in a climate where you get more than a few inches of snow
in one storm, the compressor will likely be wall hung 4'-8' off the
ground.  Otherwise, it will be on a plastic or concrete pad.

Again, just a shot in the dark.  Seems like a possibility considering
it's more or less continuous during cold weather.


On Mon, Sep 23, 2013 at 9:58 AM, Gary Tuck <gtuck at mac.com> wrote:
> Last winter I had almost steady RFI most every day, most hours of the day.  It seemed to begin when new neighbors moved in next door.  As the weather warmed in the spring, the RFI disappeared.  Then the neighbors moved and I had hope they took the noise source with them.  They are gone but the weather cooled yesterday and the noise is back.  The house is vacant.   So, now I have to get serious.  The only sources I've had in the past are power line noise and defective lights.  I've tried turning off every circuit in the house last winter and I'm convinced it isn't within our home.  It's steady, raspy but not sputtering. I was assuming that it is a portable heater of some kind but what common sources are there related to cold weather?  What might I be looking for?
> Thank you!
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