Re: tlug: Linux telecom nexus

[Karl-Max Wagner <karlmax@example.com>]

> How about the idea of feeding the signals into the public electricity supply
> system? There is an article in this weeks New Scientist
Oh, that crap. Is it cropping up again ? Actually, this has been
used for a long time for telephony on high voltage lines by
power companies. The problem is huge interference levels. There
is also the problem of line reflections, which, however isn't a
big deal with FDMA.
> (http://www.newscientist.co.uk/ns/980530/news.html) about an alternative ultra
> fast internet access system using the mains supply as the carrier. They claim
> data transfer rates up to 1000 kbits/ second. Unfortunately, they found with
Until the next guy turns his power drill on. Then you get
interference transfer rates with that speed.
> their trial system that streetlights connected to the same system turned into
> antennas, broadcasting lots of rf!
Obviously. They are gas discharge lamps and practically
shorts...well actually switches that switch on and off twice per
period. About the worst troublemakers there are. If they only
found that out only after trials, they are downright
incompetent.

They might have a bit of luck where naked wires are strung on
top of poles - but only if there aren7t any transformers are in
between. If you have a buried system, you have PVC insulated
cables - unshielded, with soil outside. About the worst
dielectric imaginable. I didn't measure yet, but I'd expect huge
losses, so in that case this system is grounded. Literally and
definitely.

Unfortunately rf engineering is a vanishing art. Not very
asonishing - to gain mastery in it it takes many years of
frustrating labour. Even worse, I don't know about any
university where students get real classroom education from an
old, seasoned hand - mostly because those old, seasoned hands
never become professors. Most professors in my experience chew
up lots of mathematics and theory, but never have made any more
demanding piece of equipment made work. And so the art is
decaying. Even worse, many old hands even switch to computing
because there's more money in there.

The result are people who try to set up communications system
without even the foggiest ideas about rf enginnering, which is
the basis of it - and, voila, braindead ideas like the above are
created, lots of money wasted with field trials which
subsequently fail - if an old hand would've been asked they
could have avoided all that expenses.

Somebody once said that humanity doesn't grow with the
perfection of its means. Sad, but true.....

                              Karl-Max Wagner
                              karlmax@example.com
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