RadioBanter - View Single Post - NPR "Morning Addition" article paints BPL as rosy solution for rural broadband.

August 18th 05, 11:06 PM

wrote:
On 17 Aug 2005 09:55:16 -0700 wrote:

| The "notching" solution is simple: Their BPL system does not use
| frequencies that are also ham bands. Whether it works or not is an open
| question.

What about MARS and SWL frequencies?

That's unclear. If covered, the result is more notch than coverage.

| - BPL is a "last mile" delivery method, not a complete system. Still
| needs a 'head end'

I've seen pictures of these units on primary (12 kV) lines, so by
"last mile" this must mean more than just the drop into the home.

What is typically done is that fiber or other highcapacity
communications is brought to a point (the injector) near a bunch of
customers. Then the signals are converted to the frequencies used by
the BPL system and put on the medium-voltage distribution line. (Note
that a distribution line and a transmission line are not the same thing
to powerco people).

At each stepdown (service) transformer, there's a coupler to take the
signals around it, because such transformers are very lossy at BPL
frequencies. They're
intentionally designed that way to keep noise and surges off the
service drops.

Which means that the couplers will bring HF noise and such into
customer's houses.

The distance from the injector to the customers served is typically
measured in hundreds or thousands of feet, not miles. The MV
distribution lines are not used forlong- or even medium-distance BPL
transmission - too lossy.

| - BPL bandwidth is shared between users on the same line, so as your
| neighbors sign up and use the system, your performance degrades.

On what line? The primary (12 kV) or the secondary (120/240 V)?

Both. Let's say you have an injector site that feeds a few thousand
feet of MV line, and there are a dozen or so transformers on that
line, each with its own coupler, and customers.

The available bandwidth is shared by all the customers on that
injector.
If there's (say) 5 mbd available from that injector and only one
customer
is active, s/he gets all 5 mbd - 100 times the speed of dialup! But if
there are 20 customers active, they all have to share, and may get only
250 kbd each. Which is only 5x the speed of dialup!

(Numbers are only for the purpose of illustration)

It's like the situation experienced by people with a DSL or cable modem
connection and multiple computers in the house all online at the same
time,
except that you have to share with the whole neighborhood, not just
Junior
upstairs gaming.

| - There are other technologies (like Wi-Fi) which can do the same job
| without all the fuss and bother.

These are on 12cm and 5cm from what I have heard.

Yup.

| - The big danger of BPL is that it turns the whole idea of spectrum
| protection and allocation upside-down, and sets a bad precedent.

It can also be susceptible to ham transmissions, which will unfairly blame
the ham radio operator as the cause of networking failures.

Once word of that gets around, hams may be blamed even if they're *not*
the cause!

Ultimately the rise and fall of BPL will depend on whether it can
compete
in the marketplace with DSL, cable, and other methods. Hopefully it
cannot.

While hams, ARRL, IEEE and others were not able to completely stop BPL,
neither were BPL proponents able to get the rules changes they wanted,
either. And actions by groups like ARRL spread the word of the BPL
threat early on, rather than waiting until the systems gained a
foothold.

There have been several instances where test BPL systems were shut down
as being impractical. Some municipalities that were looking at BPL
eventually said "No thanks" due to the issues raised.

Meanwhile, the competing broadband solutions become more available
and more affordable.

73 de Jim, N2EY