BPL strikes another win ...
 

John Smith I wrote in news:fa8ql8$d5s$2
@news.albasani.net:

John Smith I wrote:

...

Or, to sum up the previous post, digital, like cw, will get through when
nothing else will ... or, have you ever copied cw as a heterodyne on
some key clowns jamming signal?

Lots of times. My CW error-correcting hardware is excellent, is always on,
and conveniently located in my head.

But you're missing my point. A modem is always an analog device. And if
it's listening on a frequency with a loud signal on it, then it can be
saturated by that signal. I've not seen many that could copy the
heterodyne. Mostly they just stop giving any recovery at all.

--
Dave Oldridge+
ICQ 1800667

BPL strikes another win ...
 

Dave Oldridge wrote:
At worst, I'd
drive the BPL machinery to other parts of the band from where I was
working....

At worst some neighbor would get ****ed off that you are messing up
their Internet and start a FUD campaign to force you off the air for
"dangerous radiation".

It happened here with the cell phone companies and as a side effect
anyone with more than 20 watts output needs to get their station
certified as safe. I know there was a chance of hams getting a
blanket excemption, but I don't know if it was approved or not.

Geoff.

--
Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM
IL Voice: (07)-7424-1667 U.S. Voice: 1-215-821-1838
Visit my 'blog at http://geoffstechno.livejournal.com/

BPL strikes another win ...
 

BPL strikes another win ...
 

John Smith I wrote:

Digital is not analog, when adverse conditions have made an analog
signal totally unusable, a digital signal, most likely, may still be
achieving 100% error free data transfer--it is just the nature of the
beast.

Hi John,

The error here is that that digital signal in a bpl setting is trying
to function in an analog world. And for all practical purposes, while it
is on the line and till it hits the modem, it is just another RF signal.
Disregard the 1 and 0 aspect, and think about the rapid stream of
pulses. Each one on it's own is just a "state of 1 or 0, but taken
together, they are pulses that occur at RF frequencies in toto.

So here you have a string of pulses that are running at say 10 MHz. If
no other signal gets into that line, all is well. But that same line,
which can inadvertently radiate outward, can pick up another signal on
the same frequency - and it is very likely that whatever frequency you
might be transmitting on will affect it, since the pulsed frequency
equivalent (sorry for the goofy term, I'm not sure what else to call it)
varies by quite a bit, thereby making it vulnerable to lots of different
frequencies being transmitted.

Then if say the local school bus company is transmitting on some
frequency near the BPL line, that power line might pick up some of that
transmission, and send it down the line into someone's modem. That modem
won't be able to make any sense of the messed up packets it is
receiving. It'll call for a resend, and receive more gibberish.


The "intelligence" of the software controlling the data transmission(s)
is the single most important factor--as logic would dictate. Even under
almost total saturation (it would be virtually impossible for 100%
saturation, baring hooking the kw+ rig directly to the power lines) of
the BPL signal some type of heterodyne would be occurring with the KW
signal.


A packet is a surprisingly delicate thing. It takes nowhere near
hypothetical 100 percent saturation with an RF signal to change one bit,
which can disrupt a packet.


Digital is magnitudes more robust than analog, again owing to the very
nature of the beast and the simplicity of the on/off, pulse width,
timing nature of the signal.

John I might respectfully suggest that you do a little studying on the
nature of digital signals. I've been dealing with them since the late
70's, and they aren't anywhere near as robust as you believe.

- 73 de Mike KB3EIA -

BPL strikes another win ...
 

Owen Duffy wrote:
(Geoffrey S. Mendelson) wrote in
:

...
At worst some neighbor would get ****ed off that you are messing up
their Internet and start a FUD campaign to force you off the air for
"dangerous radiation".

Interesting that you mention that.

Some of our good friends in Tasmania started a FUD campaign to scare
ordinary electricity consumers about the electromagnetic raidation hazard
of electric blankets when they were BPL 'enhanced'.

Good grief. The answer is to power them with DC, and tell 'em that it
will serve as a magnet, thereby allowing magnetism's great healing
properties. Could sell little boxes with diodes in them. Maybe a crystal
or two for harmonic hegemony and celestial peace too.... ;^)


There is some steady, sound engineering / scientific work going on to
discover and reveal the impact of BPL, it is small in scale but IMHO
credible and ongoing. Uninformed and redneck comment from the amateur
community makes the job just that much harder.

I find much of the commentary very uninformed. Much of this has to do
with the Digital folks not understanding the RF folks, and vice versa.
Especially alarming is the digital folks not understanding that a high
speed digital signal is for all intents and purposes an RF signal. It
isn't 1's and 0's any more, it is an RF signal until it gets into the
computer.


Of course, the RF savants have a hard time understanding things like
"Whaatya mean Vista dropped my IP address, and the only cure is to
reboot. It's been working for three days now - it just couldn't suddenly
quit. Electronics doesn't work like that!"

At that point, I offer them the choice of being right, or getting
things working.

- 73 de Mike KB3EIA -

BPL strikes another win ...
 

Dave Oldridge wrote:

...
Lots of times. My CW error-correcting hardware is excellent, is always on,
and conveniently located in my head.

But you're missing my point. A modem is always an analog device. And if
it's listening on a frequency with a loud signal on it, then it can be
saturated by that signal. I've not seen many that could copy the
heterodyne. Mostly they just stop giving any recovery at all.


There are very rugged modems. Most people just accept the modem which
was included with their computer. A cheap modem implemented, almost
totally, in software; these can exhibit poor performance.

You get what you pay for, and like I say, BPL is a developing
technology; or, in other words, problems must be found before they can
be fixed. Your KW+ signal will be a great aid, possibly, in that
direction ...

Having worked in the software/algorithm/data-compression aspects of
modems, I have experienced high levels of line noise on standard modems
which needed new techniques to solve ... Although I have seen many
instances where line noise is at such levels even speech is horrible,
and data xmission slows to a crawl, there are few instances where it
becomes absolute zero--baring the physical disconnection of the line.

If you are inducing interference of a noticeable level in a persons
home/business that is noticeable, it will be more than just noticeable
on the BPL modem!

Regards,
JS

BPL strikes another win ...
 

Dave Oldridge wrote:
John Smith I wrote in
:

Dave Oldridge wrote:
John Smith I wrote in news:fa4i2a$jve$1
@news.albasani.net:

Dave Oldridge wrote:

...
You need a good book on digital error correction algorithms in
digital communications.

Unless you have constructed a real rf jammer (white noise really),
BPL will eat up any legitimate amateur communications you can throw
at it ... however, rumors do prevail, like the one about the tin
foil hat.
So how is it gonna eat up having its receiver saturated? I'm pretty
familiar with digital comms and, with the exception of some pretty
slow speed stuff designed for weak signal work, most of it is not
very good unless you have a really solid signal-to-noise ratio. I'm
just saying that if it's getting out to my antenna that loud, then my
kilowatt is gonna have a fair chance at saturating the thing's
receiver. And the more noise they make, the more I'm apt to have to
use the kilowatt to shout over them.

Of course in our current enforcement situation here, I'd probably
simply be told to stand down and have to go to great legal lengths to
appeal the ruling.

Digital is not analog, when adverse conditions have made an analog
signal totally unusable, a digital signal, most likely, may still be
achieving 100% error free data transfer--it is just the nature of the
beast.

Actually, I've found that, except for very slow data rate stuff, digital
signals require a BETTER signal-to-noise than analog to be readable. And
there is no partial readability with most of the commercially-used
digital modes. That is to say you either have error-free transmission or
none whatever.

The "intelligence" of the software controlling the data
transmission(s) is the single most important factor--as logic would
dictate. Even under almost total saturation (it would be virtually
impossible for 100% saturation, baring hooking the kw+ rig directly to
the power lines) of the BPL signal some type of heterodyne would be
occurring with the KW signal. Since digital is simply detecting an
ON/OFF signal, in conjunction with spacing/length of these, an on/off
signal is still detectable in this heterodyne--given the software is
aware and capable of reading this signal and switching "modes" to do
so, no harm is done to the data ... and without doubt, new error
correction methods will also develop as BPL grows and
hf-rf-terrorist-hams challenge this system ... LOL!

You cannot recover data with a modem whose input transistor is biased off
by rectified RF. I know this. I've tried it.

Digital is magnitudes more robust than analog, again owing to the very
nature of the beast and the simplicity of the on/off, pulse width,
timing nature of the signal.

The only real advantage digital has is its error-correction algorithms.
Those can do very good work when they actually have enough data to work
with. But once the data recovery by the the very ANALOG device that is
receiving the signals drops below their threshold, then the recovery
becomes terrible. Some modems are better than others. My old Telebit
19.2K could suck 1200 baud recovery out of a phone line you couldn't talk
on. But give it a couple of volts of RF in the mix and it would drop
stone cold dead. And BPL has the "disadvantage" of not being able to
filter our frequencies AND use them at the same time. At worst, I'd
drive the BPL machinery to other parts of the band from where I was
working....



Obviously, we have NOT seen the same equip/software/algorithms and
successes ... dream on ...

Regards,
JS

BPL strikes another win ...
 

Michael Coslo wrote:

...
John I might respectfully suggest that you do a little studying on
the nature of digital signals. I've been dealing with them since the
late 70's, and they aren't anywhere near as robust as you believe.

- 73 de Mike KB3EIA -

It is as if you have looked at one form of plant life and declared all
plant life the same.

How you choose to implement digital, timing with pulses, pulse
durations, etc., or any combination--takes digital into the world of
variety. Although it can be difficult to get the machine code out of a
modems hardware and study it (really impossible for the avg computer
user), astute hacker/programmers do it all the time.

You are stuck in the "already all is known world" and see every new and
interesting problem as halting to that technology in question. Mans
history reveals such thinking to be the lie it is.

We deal in computers, we deal in a world where nothing is
impossible--some things just ain't been done yet ...

Regards,
JS

BPL strikes another win ...
 

A packet is a surprisingly delicate thing. It takes nowhere near
hypothetical 100 percent saturation with an RF signal to change one bit,
which can disrupt a packet.


Digital is magnitudes more robust than analog, again owing to the very
nature of the beast and the simplicity of the on/off, pulse width,
timing nature of the signal.


John I might respectfully suggest that you do a little studying on
the nature of digital signals. I've been dealing with them since the
late 70's, and they aren't anywhere near as robust as you believe.

Depends a lot on the encoding technique used. Amateur HF packet using
surplus Bell 202 modems is pretty bad in terms of interference handling.
COFDM with a rate 1/4 FEC is pretty good.

One needs to select a coding suited to the channel (e.g. using the
coding used for getting 56 kbps through a 3kHz phone line is probably
not appropriate for a ionospheric HF path).

I would venture to say that with today's technology, one should be able
to get within 0.5dB of the Shannon limit without too much trouble. So,
since a BPLish signal can be many MHz wide, and the putative interfering
signal is going to be pretty narrow band in comparison, they can code
around it.


- 73 de Mike KB3EIA -

BPL strikes another win ...
 

In article ,
Jim Lux wrote:

I would venture to say that with today's technology, one should be able
to get within 0.5dB of the Shannon limit without too much trouble. So,
since a BPLish signal can be many MHz wide, and the putative interfering
signal is going to be pretty narrow band in comparison, they can code
around it.

For a relatively weak interfering signal, that's probably true.

That's not likely to be the case in a lot of situations, though. A
strong interfering signal - say, a few watts of HF coming from a wire
antenna, a few houses away from a BPL receiver - is likely to be
strong enough to saturate the RF front-end of the BPL receiver. This
will result in a severe "de-sense" problem - it'll wipe out most other
signals within the receiver passband.

Ham (and other narrow-band) HF receivers deal with this problem by
limiting their receiver passband. Single-band filters prior to the
first mixer or first RF amp will keep out interferers outside that one
band, and narrow-bandwidth multi-pole filters after the first mixer
can reduce the impact of interfers that are closer to the desired
signal.

This approach doesn't work with systems which have a "wide-open"
broad-bandwidth front end, such as a typical BPL receiver, as the
receiver's front end *has* to be left open to the entire bandwidth of
the desired incoming signal. Many modern ham HTs have similar
problems... their "DC to daylight" front ends are easily desensed, or
driven into severe intermodulation by nearby VHF transmitters (e.g.
police, fire, paging, and so forth).

I imagine it's possible to reduce the severity of a BPL receiver's
desense problems by using a wide-dynamic-range front end... but these
take more power and aren't as suitable for large-scale chip
integration, and are thus going to be more expensive to build.

Even a "ham-friendly" BPL transceiver, with deep transmitter notching
of the ham-band frequencies, is likely to have trouble when it finds
several volts of (e.g.) 40-meter RF coming into its input terminals.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
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