From: John Smith on Sun 7 Aug 2005 23:27

Len:

Phone lines are limited to roughly 38K by using the full audio bandwidth a
phone line is filtered to, with the early compression techniques. 56K is
obtained by improved data compression techniques.

Any line capable of supporting transmission of these audio freaks can
carry that much digital data (roughly +/-300hz to +/-5,000hz.

[small point of order, upper limit about 3.4 KHz, no huhu...]

Both AM and PM at discrete increments push at the upper limit
by using more increments (enabling more states) but that
increases the probability of error. The present "56K" standard
is a compromise. The combinatorial AM-PM makes throughput
greater than either AM or PM by themselves...not easily explained
in text, needs graphical plotting.

DSL is obtained by pulling all the filters from the line, audio bandwidth
is much expanded and much greater data can be crammed into that bandwidth,
with even greater efficient compression techniques.

True, and the providers are able to cram more charges onto one's
bill for that...:-)

Powerlines can support near/equal such bandwidths. With a bandwidth
allowing freqs to climb into the LF RF freqs, tremendous data speeds are
possible.... very localized interference to some rf freqs may be
generated... this is now in a testing phase...

In theory the Access BPL (what the FCC now calls it) can do
roughly 50 to 100 MBPS on proposed systems. That's on par
with the downlink cable TV services providing the same thing.

The MAJOR problem with Access BPL running through one's
neighborhood is that those can kiss their HF receiver
sensitivities bye-bye. Most of the tested BPL systems raise
the sensitivity floor 30 db or more.

By the way, it would seem that the Office of Engineering
and Technology at the FCC is getting stiffer with the BPL
providers. Saw this in scanning the Federal Register
contents looking for a Notice on WT Docket 05-235...it isn't
all on the OET page at the FCC website. The techno people
may be "getting even" in a small way with the political people
at 455 12th St SW. :-)

Why this is so misunderstood is beyond explanation, or perhaps it is only
limited to the older generations, for some unknown reason--as any familiar
with technical details of data transmission methods and protocols should
know this, it is very basic stuff...

IRRELEVANT to the amateur radio publications' editors. Those
guys have to bow to pressure from their front office people
(publishers) and "make it simple" for the readers. They seem
to be of the opinion that hams are JUST radio operators. Since
the periodicals NEED advertisers to pay their way, they tend
to kowtow towards the advertisers offering hardware.

"Sidebands" as a result of modulations go only so far as voice
transmissions in the ham "textbooks." [operators don't need
smarts on theory?] Publishers and editors don't shine
spotlights much on anything but AM voice sidebands...which may
be THEIR deficiency. Radio amateurs get their theory where
they can and that is mostly from the periodicals. If that
theory ain't in those issues it seldom gets to the ham ops'
heads. The publisher decides what goes in them magazines.

You may not have seen the ham magazines of the 50s when
single channel SSB voice was beginning to take off. There
was great antipathy towards PHASING methods of modulation-
demodulation of SSB. Hams weren't told about PHASE, didn't
have the tools to see phase, few could afford 'scopes that
had passbands beyond 5 MHz. It was EASIER to build filter
SSB mod-demod even though it CO$T a lot more for those crystal
filters. Less thinking involved. AM voice spectra was
easier to understand and "brute-force" filtering to eliminate
an unwanted sideband almost intuitive. Despite some good
attempts at showing PHASING methods in the 50's magazines,
readers and editors alike didn't like it. Even after Mike
Gingell (UK ham, now living in USA) did his Polyphase Network
PhD paper on a low-cost, easy-component-tolerance quadrature
phase circuit, the U.S. periodicals didn't care for it. The
RSGB did and showed How and showed what UK and Yurp hams
were doing with it in the pages of Radio Communication. That
was 30 years ago...but European hams are having fun with that
Gingell polyphase network in homebrew SSB building.

When it comes to Spread Spectrum and the Discrete Sequence SS,
forget trying to explain the sidebands generated to radio
operators. That subject doesn't help them win contest points
or "work the rare ones." ["we" hams don't use that snit!]
Forget spectra pictures of any modulation other than AM with a
pure sinewave modulation input. Agreed, FM or PM at various
modulation indexes can get confusing...H-P (just before they
changed name to Agilent) had a neat "movie" on varying the index
and showing how the sideband content changed, was done on their
website but can't be done in printed magazines. FM broadcasters
commonly calibrate their modulation indices by the "carrier null"
method where, at a certain modulation index with a given
frequency mod signal, the carrier goes to minimum power as seen
on a narrowband detector. That's been happening for over 40
years, a well-known technique.

Nah, hams don't need all that (hack, ptui) THEORY. All they
need is high-rate MORSEMANSHIP! to be extra-super-special.
Screum.

bit off