[NCham] BPL Update, Raleigh, NC, April 6, 2004

[Gary Pearce KN4AQ]

4/6/04, Raleigh, NC

Progress Energy is making an active attempt to avoid using Amateur Radio 
spectrum on overhead lines in their trial areas, with some success.

Tom N4TAB and I met with Bill Godwin today at the Phase II trial areas.  We 
reviewed the spectrum in use.  Bill had a chart showing where BPL could 
operate and avoid ham bands, and Amperion had adjusted their system to 
comply with that chart.

We found three problems.

1. They missed in the area of 20 meters, starting a BPL signal block on 
14.300 MHz instead of 14.350.  That may be a hardware or software problem, 
but more likely was an error calculating the spectrum needed.  The 
equipment interface is still rudimentary.

2. The block edges are not brick walls.  They taper with progressively 
weaker carriers which remain audible over 25 to 100 kHz of spectrum, 
depending on the noise floor (this is to a mobile about 75 feet from the 
line, running an Icom 706 MKIIG and an Outbacker Perth Plus antenna).  We 
recommended compensating for this so that the residual carriers also fall 
outside the ham band.  There is a fairly immediate 10 to 15 dB signal drop 
(estimated, over about 10 kHz) that defines the edge of the block.  The 
remaining signals are very weak, but would bother a home station within a 
city block or two of the power line.  And the goal in eliminating the ham 
spectrum would be so that the BPL could be placed on a line in the 
immediate vicinity of a ham.

3. The 17 and 12 meter bands fell inside the spectrum blocks, and are 
"notched".  But the notch isn't perfect.  They might be 40 dB down - just 
audible in the noise when the main carriers were S7, but they are clearly 
there.  Again they would bother a ham within a city block of the line.

Perhaps N4TAB or W4FAL can provide a more technical explanation of this 
observation.

The mitigation process at this iteration of Amperion's hardware is neither 
simple nor precise.  The hardware does not have a GUI interface with which 
the operator can simply type in the desired spectrum.  And the adjustments 
to date require field monitoring and feedback, sometimes followed by 
another attempt to hit the target.

Bill had arranged for an Amperion operator to be available and make 
adjustments "on the fly" while we observed.  Unfortunately, Bill's contact 
person was unavailable with no explanation (didn't answer his phone, didn't 
return a call in the 90 minutes we were there).  Bill apologized profusely 
as the time had been set up in advance.


All of our observations recently have been on the overhead power lines.  We 
have not been discussing the underground lines.  The underground lines do 
radiate locally, near the pedestals that house the repeaters.

Whether or not this scheme will work in a dense environment is still 
unknown.  Bill identified three 6+ MHz blocks of spectrum available 
(7.3-14.0 with 30 meters notched; 14.35-21.0 with 17 meters notched; and 
21.45-28.0 with 12 meters notched).  More spectrum can be used below 7 and 
above 30 MHz, but Amperion prefers to remain between 7 and 30 MHz.  If this 
spectrum can be rotated between line segments, and the notches can be 
deepened some, they may satisfy the concerns of hams for the Amateur Radio 
spectrum.

However, there is currently no attempt to avoid other shortwave frequencies.

We appreciate this proactive attempt.  We will point out again that there 
are other public uses and users of the spectrum in between the ham 
bands.  Shortwave Broadcast is the notable one, but people roam the 
shortwave spectrum listening to all kinds of traffic - military, aviation, 
business, government - anything transmitted "in the clear" is legal and 
often interesting to monitor.  Amateur Radio operators are often part of 
this group of listeners, and in any case we can not sit back and say, 
"Well, our problem's solved.  Good luck with yours!"

Today, a shortwave radio listener can roam the bands at will, contending 
with a variety of natural noise and an increasing amount of man-made noise, 
but for the most part listening freely to the full spectrum.  BPL, as 
configured today, would change that reality for any listener within a 
half-mile of a power line.  In other words, everyone.

For this reason alone we can still consider BPL a flawed concept.  If it 
appears that every time a utility makes progress (no pun intended), we 
raise the bar, that is not so.  We have been inclusive in identifying a 
variety of spectrum users fro the beginning.  Progress Energy and Amperion 
have been solving problems one at a time, and that's fine.  We just want to 
make sure that everyone understands where the goal-line stands.

73,
Gary KN4AQ

__________________________________________________________________________
        Gary Pearce KN4AQ        editor, SERA Repeater Journal
        Cary, NC                 www.sera.org
        919-380-9944             kn4aq@sera.org
        kn4aq@arrl.net
         AOL/Yahoo Instant Messanger: KN4AQ
         (send e-mail to be put on my "buddy list")