Hi Scott, You wrote: <This is broadband, from 30 MHz to > 1 GHz, at levels up to 70 or 80 dBuv. It is not like a flat carrier but > rather more like PWM driven motor noise. It lasts from 15 seconds to 1 > minute in duration. Then ambient returns to normal.>
I've had a very similar problem, 20-30dB over limit, wideband from 30MHz to 1GHz. Once was continuous, and was found to be a fluorescent fitting in a corridor about 60 feet away inside the building. Another incident, with identical EMI characteristics, but happening about 4 times a day for durations of 1 to 2 minutes, was traced to a fluorescent fitting in the Secretaries toilet! The source may be closer than you expected......... Just a suggestion, Chris Dupres Surrey, UK.
