Gives Short Shrift to Short Wave
a home amateur radio system you might hear birdies—a little
noise from your neighbor's computer or outside lamp post. But the
computer and the light are not emitting all the time or on all frequencies,
explains Edward F. Hare Jr., RFI laboratory manager for the Amateur
Radio Relay League (ARRL). Moving to another frequency usually solves
the problem. Broadband over power line (BPL), however, fills tens
of megahertz with birdie after birdie and uses a chunk of spectrum
that operates 24 hours a day on overhead power lines. To an amateur
radio operator, that means interference on any frequency.
typically occupies between 5 and 25 MHz of spectrum and operates
in the frequency range between 2 and 80 MHz. BPL technology has
been supported by President Bush and is gaining ground commercially
in the United States.
a recent letter to FCC, ARRL called on the agency to reconsider
its rules adopted last October. According to ARRL, "FCC incorrectly
rejected the league's recommendation for a 20-dB extrapolation factor
in measuring BPL signal decay on HF based on distance from the signal's
radio uses very weak signals. Adding notched BPL noise causes
significant degradation and makes it difficult to copy weaker
signals," says Hare. "It connects using radio signals
and becomes like a giant antenna."
problem is that it is difficult—if not impossible—to
completely protect short-wave signals with notching in a fully
deployed BPL system. According to Hare, it takes months of fixing
to remove interference even from a small, local system. It would
be nearly impossible to address such interference in a system
that covers an entire state.
has gone to great pains to avoid the short-wave bands," says
Hare. Other companies, he says, are also heading in the right
direction with the development of their systems. According to
ARRL, the fact that Motorola has taken steps to mitigate the interference
means that it is not unreasonable for FCC to set appropriate limits.
"Short wave is the only spectrum where you can fully communicate
without the help of an intermediary, like a satellite," says
Hare. According to ARRL, there are currently more ham radio operators
EMC Standards Development Committee is addressing the standardization
of EMC measurements of emissions from power lines. According to
Don Heirman, the committee believes that these radio services
should be allowed to be present, "providing that the EMC
aspect of noninterference is maintained with the radio service."
Heirman, vice president of standards for the EMC Society, announced
these activities in the Spring 2005 EMC Society Newsletter.
The EMC and Power Engineering societies have formed a joint
study group to address measurements.
that may not be enough. The time to address these interference
problems is now, when there are still relatively few commercial
sites. FCC must keep its promise that offending systems will be
required to resolve interference issues.