I think a general description of other RFI sources would be helpful for any
radio amateur to make a 'first cut' assessment. It might also help you
isolate
the truly legitimate cases of BPL RFI--if and when they exist.

There are several RFI sources that would be the most common ones misidentified
as BPL. The first is "conventional" power-line noise. It is usually
characterized by having a *noisy* 120-Hz component, as the sparking takes place
on the positive and negative peaks of the 60-Hz wave. Another is similar,
occurring from things like lamp dimmers, motor controllers, flourescent lights,
etc. Those sources usually have a 120- or 60-Hz component, but the noise on the
peaks is usually quite a bit less noisy looking.

Switch-mode power supplies can also be noisy, but they generally have noise
that ranges from reasonably coherent (carrier-like) to broad, buzzy clumps of
noise, spaced every N kHz, where N is the free-running rate of the switcher
frequency. N is typically 10-50 kHz or so. Some switchers make noise that is
fairly close to gaussian-distributed noise, with a pretty uniform
distibribution of power vs frequency (power spectral density). One key
diagnostic for a switcher is that the N kHz tends to drift around a bit. A
series of noisy carriers or clumps of noise that are spaced every 15 kHz, for
example, may drift up the band as the unit is turned on and warms up over an
hour or so. If so, it is almost certainly a switcher.

(I do, btw, suspect that the "plasma tv" problem is really a switch-mode
problem, as some amateurs have reported no interference from plasma TVs. On my
long list of things to do is to take the Lab's Icom R-3 receiver to the local
big electronics store and see if I can get some estimates of the noise level
from various equipments.)

Probably the most diagnostic, however, it the distribution of noise signal vs
frequency. BPL is designed to use specific spectrum, and as one tunes a general
coverage receiver from 2 to 80 MHz, its onset will be rather sudden, it will
persist for at least several MHz, then taper off just as abruptly.

I do have a concern that hams not make too many false alarms. Sounds like you
are on top of the the problem and I wish you the best.

There are no guarantees, but I am hoping that by talking to each of the hams
that report BPL interference, between them and me we can reach the correct
conclusion. If things don't add up, I will suggest that it not be reported.
Each report of actual interference is precious right now, and I would be
willing to go to the trial area to verify a questionable case.

Thanks for your interest.

73,
Ed Hare, W1RFI