In article , Mike Coslo writes:

Len Over 21 wrote:

Mike, the "X10" system works at only a few hundred Hz of spectrum.

I'm not familiar with the specific names. X10 is the one the power
companies use?

No, it's a long-on-the-market home appliance remote control and
alarm system, available at places like Lowe's and Home Depot
among many. Search for "X10" on the Internet and you can find
their website and product explanation.

There was another system that was used to control clocks in schools and

other places where the clocks need to show the same time over

Those were still very low-frequency. For clocks with synchronous
motors, the separate clock AC line could be speeded-up or slowed-
down by a separate AC source (synchronous clock motors don't
take much AC power). For some systems, a separate control line
was used to set the hands to a particular time all at once to make
them read the same. WREX-TV in Winnebago, IL, had still another
system combining a WWV receiver checking the time of a master
pendulum clock through the background tone-on from WWV and
then syncing all the clocks in the station running on their own AC
circuits. In master control we used the master pendulum clock
since every second counted (for cash flow) on taking network (CBS
at the time, coming up precisely 1.0 second after the hour or every
half hour).

At no time was any part of the US electrical distribution system, home
to generating plant, EVER CHARACTERIZED OR STANDARDIZED
AS R.F. TRANSMISSION LINES OVER A 1 TO 80 MHz FREQUENCY
RANGE!

Apparently the Office of Engineering and Technology at the FCC doesn't
understand that yet...?

I can look out at my neighborhood's electrical distribution system and
see "RF transmission lines" that must vary from several hundred Ohms
to just a few Ohms within the metal conduit of my home.

That is NOT any sort of "RF transmission medium" that anyone can
expect to work at either smooth, easy, or trouble-free radio frequency
transmission. There's discontinuities up the ying-yang there and
wherever there are discontinuities, there is also the danger of even
more radiation (in addition to introducing more attenuation).

So if this was (is) such a good way to send signals, why wasn't the
internet developed this way in the first place?

For the simple reason that it does NOT work very well. :-)

I guess I was kind of knowing the answer as I asked the question. 8^)
It's intellectual dishonesty for those companies to try to sell it as
something that will work.

I'm sure it can work...the question really is "can it be used anywhere
with the ease at which existing wired service does?"

When each and every BPL proponent HAS NOT EXPLAINED THE
TECHNICAL DETAILS OF THEIR SYSTEM, they can't actually be
charged directly with "intellectual dishonesty." At this point it is all
the usual marketing-advertising snow job.

But even if it is a failure, some will be able to make money on it..
for while.

That's usually the case. See the fancy bar-code reader that Radio
Shack was promoting as part of a "system" to speed up information
exchange. IEEE Spectrum magazine and a couple of other trade
publications have spotlighted that one.

The point with BPL now is still vaporware. It WILL increase the
noise environment from MF to bottom of VHF but it is impossible to
get a quantitative handle on the spectral power. Getting technical
details is like nailing jelly to a tree...it doesn't work and everyone gets
sticky from all the sugar in the jelly.

The ARRL Lab did the best they could with the BPL technical info
available. They used the maximum RF radiation specs from Part 15
in modeling one transmission line (so-called "MV" distribution in a
neighborhood). Their model was as "good" and "accurate" as the
circumstances allowed...and doesn't actually model a BPL system
because the exact nature of the BPL systems isn't explained!

The problem with such modeling is that the actual MV distribution is
HIGHLY variable depending on the city, district, neighborhood, etc.
The spacing of the conductors (which determines equivalent RF
characteristic impedance) is highly variable even if within the NEC and
local codes. For SOME distribution systems BPL uses those MV
lines (voltages from 4 to 12 KVAC). There's absolutely nothing in the
National Electrical Code or even any local ordinances that mandates
any characteristic impedance of those lines or standardization at RF!

I've got a pair of Phonex through-the-line coupled "modems" that are
supposed to work between two rooms here. It's the second pair over the
counter, the first pair returned because they don't work well. Second
pair is no better.

One good reason why they don't work is that the AC wiring in one room
is on one side of the "double-phase" split from the pole drop and the
outliet
in the other room is on the other side. Neither Phonex or any other of
the
Homeplug group explains that.

I can hear it now.........."We need to rewire your house to get your
BPL modem to work!" 8^)

None of us have any idea of how those "BPL modems" work...the BPL
folks won't explain it... :-(

I measured an attenuation from the AC outlets better than 30 db from
10 to 80 MHz, 36 db being lower limit of this setup. The attenuation is
probably greater than that. No sense in improving the test setup with
that much attenuation...it is already too great.

Interesting. As a comparison to my cable modem hookup, There was a lot
of adjusting of the line levels to get a good signal to my home office.
If the installation included boosting the power enough to overcome that,
there would be some serious RFI running around.

You have higher speed than 56K?

I believe that I am skeptical enough that even if I didn't have a
technical background, that question would pop up pretty quickly when
considering BPL.

Carl, is there any other way that we can aid this fight?

One of the first things to try is to force an explanation of how all the
vaporware BPL systems work. NONE of them explain it in enough
detail to make any electronic sense right now. They haven't done so
in any of the prominent electronic trade publications yet...other than
more generalized, non-specific-detail claims. Vaporware.

Agreed!

Initially, there was an UNWARRANTED Hue and Cry by the "radio
community" (two BPL proponents' name for ham radio) in that "RF
interference would be too high!"

Since NO ONE had any specific RF line level information on BPL
systems, it was really impossible to determine whether those levels
were "too high," "just right" or "too low." The ARRL model was
done solely on RF levels being at a certain maximum level that was
not determined from any specific BPL data.

Instead of acting in group hysteria, the "radio community" should
have gone into basics and demanded more details of the BPL systems
both in hardware and expected technical performance. For a bunch
of supposed RF-savvy radio activists, damn few ever considered the
AC power lines as RF transmission lines or the VARIATION of lines'
characteristics at RF.

Picture an RF transmission line spaced for about 1000 to 3000 Ohms
connected (somehow, unknown) to 75 Ohm coax as a basic model.
Then consider that the RF xmssn line is really a triplet with a
common in the center and the "coax" is really Twinax (a shielded
twisted-pair, sort-of). Intuitively, it's going to be one bitch of a task
to get a 7 to 8 octave frequency match of one line to the other. If
the match isn't good, then the reflected RF is going to go someplace
and that is back out the MV line and probably radiated instead of
being absorbed (by unknown "terminations").

The BPL types would have been better off to just consider a fiber-
optic cable carrying high-speed data both directions...and that
mounted in the pole space of the MV lines. No conductors and
the fiber-optic cable couldn't short out the MV lines and the MV
lines wouldn't interfere with data on the fiber. Sharing "pole space"
could have been their schtick instead of thinking that RF can flow
easily on an AC power system never designed for RF.

LHA