I'll have no more to say on this. I did think several might be interested
in the topic though.
(509) 982-2181 Equipment sales
(408) 907-6910 (Vonage) Consulting services
42846865 (icq) And I run my own wisp!
188.8.131.52 (net meeting)
----- Original Message -----
From: "Gary A Hoffman" <firstname.lastname@example.org>
Sent: Tuesday, August 03, 2004 10:12 PM
Subject: [WISPA] Beware the BPL Buzz
Beware the BPL Buzz
August 2, 2004
By <mailto:email@example.com>Peter Coffee
Bad things happen when ideal IT concepts bump into the realities of
imperfect hardware. This time, I'm talking about the slow-motion train
wreck of BPL (broadband over power lines), a basically bad idea that's now
the subject of a newly launched IEEE standard process.
With lots of people wanting its benefits and few people understanding its
drawbacks, BPL seems likely to gain too much momentum to be killed. A win
for BPL, though, could be a loss for some valuable applications of the
radio spectrumbut you'd never know that there's a serious risk, or even a
controversy, if all you saw was the IEEE's cheerful July 20 announcement of
IEEE P1675, "Standard for Broadband over Power Line Hardware."
The IEEE announcement calls the BPL proposition "relatively
straightforward," saying "A computer-router combination and a coupler take
the signal from an optical-fiber cable as it enters a substation and
imposes it on the electric current. The signal travels over the
medium-voltage lines, with repeaters placed every 0.5 to 1 mile to keep the
signal viable. A repeater/router near a residence or business extracts the
signal off the medium voltage just before the transformer and injects it
onto the low-voltage wiring on the other side of the transformer. The
signal is now on all of the low-voltage wiring within the structure and can
be accessed at any outlet by plugging in a modem."
The elephant in the living room prompts my follow-up question: "Where else
is that signal accessiblewhether it's wanted or not?" Incredibly, the
words "radio" and "interference" are not even mentioned in the IEEE
announcement, even though the risk of radio interference from BPL is
obvious and grave.
BPL proposals place data signals on carrier channels that span a broad
swath of frequencies. Those carrier frequencies overlap those used by
everything from international shortwave broadcasts to standard time signals
to CB radios (remember those?) to baby monitors to the low end of the range
of TV channels. Although not intentionally radiated, those BPL signals will
be traveling on wires that can't help but behave to some degree as antennas.
We keep signals confined, on a small scale, by precisely tailoring signal
paths in chips and on circuit boards. We control them on a larger scale by
using shielded conductors, or twisted-pair lines that cancel stray
radiation by combining equal and opposite components. And when we need to
convey a complex signal at high power levelsfor example, when feeding a
moon-bounce radio antenna arraywe don't use just an ordinary wire. We use
a transmission line, a carefully tailored component that matches voltage
and current ratios between the source and destination and that minimizes
stray radiation of signals.
Electrical power lines are designed to carry power and are optimized for
efficiency and safetynot for minimum radiation of high-bandwidth energy.
The IEEE P1675 announcement speaks about traditional power-system
priorities and quotes Terrence Burns, chair of the IEEE BPL Standards
Working Group, as saying, "Power companies face a number of issues ... for
example, how to assess the performance and safety of repeaters/ routers,
medium- and low-voltage coupling hardware and other equipment before
buying. Other issues include how best to put this equipment in place and to
keep the overall system operating well and prevent it from interfering with
power delivery. The new standard will help them deal with these concerns."
Is radio interference someone else's problem?
To be fair, some BPL proposals do include active measures for detecting and
avoiding communication interference. I'm sorry to rain on proposers'
various parades, but shortwave communications are what we turn to when
other things aren't working, and I don't like that failures in a new and
complex system could put an essential backup system at risk.
"Nearly all electrical utilities are exploring BPL because the potential
benefits are so substantial," said Burns. Yes, and there would also be
"potential benefits" in breaking the second law of thermodynamics, but no
one expects to be taken seriously if he or she proposes to try. Radio's
realities deserve equal respect from the proponents of BPL.
gary a hoffman
Wireless mailing list
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
TowerTalk mailing list