Each time I've had RFI on 30M, it was caused by a mobility scooter's
built-in switching power supply used to charge its batteries. One
scooter was next door. The other was across the street and two houses
up.
I was able to resolve the interference problem by taking a 10 foot
long IEC AC power cord (the type which has a "standard" AC wall outlet
plug on one end and the 3 pin female connector that fits the standard
AC power jack on most equipment) and winding it around a 2.5 inch Type
31 Ferrite donut 8 or 9 times and again through a 2nd donut
immediately adjacent. Essentially 2 chokes in series.
This choke then plugged into the scooter and an extension cord plugged
the choke into the wall outlet. The scooter could charge properly
without spewing trash in several parts of the 30M ham band.
In each case, I was able to hear the interference fairly well on an
Eton E5 battery operated AM/FM/SW radio. I walked around my house,
then around the nearest houses until the signal strength indicator
showed me from which house the signal was actually originating.
I'm on great speaking terms with all my neighbors so it was a simple
matter of going inside and doing a survey. When I got within visual
range of the scooter, the receiver's signal strength indicator was
popping the top of its LCD range, the radio was screaming with the RFI
and my neighbor unplugged the scooter's AC power cord to make it stop.
In the RFI business, speculation is a waste of time. If you can hear
the RFI, you should be able to find it. Once you find it, all your
questions will be answered.
Good luck and good hunting!
Frank N. Haas KB4T
Utility Interference Investigator
Florida
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