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 Previous: The K7RA Solar Update |  Next: FCC Amateur Radio Enforcement Letters for the Period Ending Apr 3, 2004 |
 ARRL PIO Gary Pearce, KN4AQ, is among a group of amateurs keeping abreast of BPL trials under way in North Carolina. |
NEWINGTON, CT, Apr 8, 2004--Amateurs in the Raleigh, North Carolina, area say electric utility Progress Energy and Broadband over Power Line (BPL) equipment provider Amperion have had "some success" in their efforts to avoid using Amateur Radio spectrum on overhead lines in their BPL field trial areas. But problems persist, and the process is far from quick and simple, says ARRL North Carolina PIO Gary Pearce, KN4AQ, who has been among local amateurs closely monitoring the Progress Energy/Amperion BPL trial. Their experiences could indicate what amateurs may face in areas where BPL is widely deployed.
"The mitigation process at this iteration of Amperion's hardware is neither simple nor precise," Pearce said this week. Progress Energy/Amperion essentially are attempting to "notch out" or completely avoid ham radio frequencies, since hams have been the only HF users so far to file interference complaints. Complicating the effort, he says, is that the process is largely hit or miss, requiring field monitoring and feedback and sometimes another attempt to nail the target.
On March 5, a BPL home demonstration in Wake County south of Raleigh provided an opportunity for area amateurs to briefly take their concerns directly to FCC Chairman Michael Powell, who was on hand for the show.
Pearce says he and Wake County ARES Emergency Coordinator Tom Brown, N4TAB--an engineer with extensive RF experience--met this week with Progress Energy network engineer Bill Godwin at the so-called Phase II BPL trial areas to review the BPL spectrum in use. Amateurs also monitored the system using an Amateur Radio mobile station some 75 feet from the line. Equipment included an ICOM IC-706MKIIG and an Outbacker Perth Plus antenna.
"Bill Godwin had a chart showing where BPL could operate
and avoid ham bands, and Amperion had adjusted its system to comply with that
chart," Pearce said. Among other issues, Amperion missed the mark on 20
meters--starting a BPL signal block on 14.300 MHz instead of 14.350 MHz, he
pointed out.
 Progress Energy's Bill Godwin (left), and Wake County ARES Emergency Coordinator Tom Brown, N4TAB, standing near the BPL power line during a January visit. Godwin's vehicle at the left is equipped with a ham radio transceiver to monitor for BPL interference. [Gary Pearce, KN4AQ, Photo] |
"That may be a hardware or software problem, but more likely it was an error calculating the spectrum needed," Pearce said. In addition, he points out, the BPL spectrum block edges "are not brick walls" but taper off, with progressively weaker carriers remaining audible up to 100 kHz away, depending on the noise floor.
"There is a fairly immediate 10 to 15 dB signal drop that
defines the edge of the block," he said. "The remaining signals are very weak
but would bother a home station within a city block or two of the power line."
He says the amateurs recommended compensating for this, so residual carriers
also fall outside the ham band. "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."
 (L-R) During a January visit to a BPL test zone, Bill Godwin and Will Roberts, AA4NC, of Progress Energy; Wake County EC Tom Brown, N4TAB; North Carolina Section Technical Specialist Frank Lynch, W4FAL, and Gerrett Durling of Amperion check out the display of a portable spectrum analyzer during BPL testing. [Gary Pearce, KN4AQ, photo] |
Pearce reports the 17 and 12 meter amateur bands fell inside the spectrum blocks and have been notched, but the notch isn't perfect. "They might be 40 dB down--just audible in the noise, while the main carriers were S7--but they are clearly there." Pearce predicted even that level of interference would bother an amateur station within a city block of the line.
An effort by Progress Energy to have an Amperion operator available to make adjustments on the fly while amateurs observed fell through when the operator failed to show without explanation. He said Godwin "apologized profusely."
All of the North Carolina amateurs' recent observations
have involved overhead power lines. "The underground lines do radiate locally
near the pedestals that house the BPL repeaters," Pearce noted.
 A typical BPL "extractor" system, this one in Penn Yan, New York. The box contains hardware to interface with the power line. A 2.4 GHz WiFi signal provides the interface to neighborhood BPL "repeater" nodes. |
Unclear at this stage is whether the "notching" scheme will work in a more-dense BPL environment. Pearce said Godwin identified three 6+ megahertz blocks of available spectrum--7.3-14.0, with 30 meters notched; 14.35-21.0 MHz, 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," Pearce said. "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." But, he adds, no efforts are under way to avoid other shortwave frequencies.
"We appreciate this proactive attempt," Pearce said. "We will point out again that there are other public uses and users of the spectrum in between the ham bands." Amateur Radio operators "cannot sit back and say, 'Well, our problem's solved. Good luck with yours!'" Pearce says.
"For this reason alone we can still consider BPL a flawed
concept," he continued. "If it appears that every time a utility makes
progress, we raise the bar, that is not so. We have been inclusive in
identifying a variety of spectrum users from the beginning." Although he
credits Progress Energy and Amperion with cooperating to resolve amateur
interference issues piecemeal, "we just want to make sure that everyone
understands where the goal line stands."
| Previous: The K7RA Solar Update | Next: FCC Amateur Radio Enforcement Letters for the Period Ending Apr 3, 2004 |
