Good point. Ed, what does a plasma TV look like compared to BPL. Is the
multidomain signature quite different?

I have not looked at a plasma TV, Chip, but I would make that diagnosis
primarily on on the basis of the sphere of influence. In the BPL test areas,
the interference was heard over the entire area that had the BPL couplers in
place.

There are other indicators, too. Knowing the involved BPL manufacturer would
let one pretty easily compare what was heard on the air to the known
characteristics of the BPL system involved. Interference from plasma TVs is
not
going to be "modulated" with digital signals, as would a BPL signal. Those
OFDM carriers in the Ambient and Amperion BPL systems would be pretty hard to
confuse with anything else.

Another characteristic to look for is spectral occupancy. If the signal
appears
suddenly in spectrum, is heard over several MHz, then suddenly tapers off,
that
also matches the BPL characteristics, not that from other devices.

If the signal is noiselike, but clearly digital in sound, one can also look
for
the bursts of the downloads, followed by the shorter, "keep alive" pulses
that
some of the systems do.

If all of the above added up and started at the same time the BPL system was
brought on line, I would feel comfortable with my diagnosis.

73,
Ed Hare, W1RF


Hi Ed,

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.

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.

73,
Chip N1IR

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

On 17 Oct 2003 11:28:37 GMT, (W1RFI) wrote:

snip

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.

Watch out for Silicon Controlled Rectifiers (SCRs) used for power
switching. They switch on the during a portion of the positive
swinging cycle generating a *sometimes* huge pulse and are usually
used in pairs. They are always 60 cycle, but as there is one on each
polarity there will be two equally spaced pulses appearing as if they
were a single 120 cycle repetition. OTOH a 3-phase system might look
a bit confusing. However the pulse train "should" be symmetrical
based on 120 degree spacing of a 60 cycle base which might give the
appearance of 180 cps. These things are bad enough that the pulses
from one system can cause false triggering in another SCR system
nearby.

snip

Precip static and in particular, snow static does a very good job of
imitating the sound of some bpl, *but* it looks entirely different
when seen as a time domain display. The static will be a display of
relatively evenly spaced pulses that will *usually* increase in
frequency over time. A single unterminated half wave 75 meter dipole
can blank out a whole city block on some frequencies. The voltages
generated can make the ignition coil in a car look puny.

Roger Halstead (K8RI EN73 & ARRL Life Member)
www.rogerhalstead.com
N833R World's oldest Debonair? (S# CD-2)

snip

Thanks for your interest.

73,
Ed Hare, W1RFI