David: Detractors also claim that BPL interrupts regular radio transmissions. In the FCC Report and Order, the International Municipal Signal Association claims that BPL interferes with emergency call boxes and the National Antenna Consortium claims that BPL within 20 miles of airports and antennas for ground-to-air communications and military bases, and within two miles of hospitals, police stations, and fire stations could cause interference. Can you please comment on this?

Chano: I'm not aware of any situation where real interference to those services has been reported.

In any case, in order to be on the safe side, the FCC has taken measurements to provide special protection to critical services and locations. The FCC Report & Order 04-245 on BPL includes the notion of "excluded bands" and "exclusion zones".

BPL equipment operating in overhead lines has to avoid "excluded bands" to protect aeronautical (land) stations and aircraft receivers. Also, BPL equipment operating within a certain distance from coast station facilities or Very Long Baseline Array facilities has additional prohibited frequency bands.

David: The ARRL's Ed Hare states "The idea that...one can just put those signals onto any old wire, is not technically supportable." Assuming BPL is technically feasible, please explain, technically, why it's feasible and further, help us understand where the ARRL's claims may be wrong.

Chano: I agree with Ed in many points, but I completely disagree with him on this one. You cannot compare the trade-offs involved in designing a BPL system with the ones involved with other systems, because they are based on totally different assumptions.

When designing a new communication system, the design engineer can decide where he or she wants to put the highest cost, requirements, or complexity: either in the end-points or in the transmission media (the cables). Many communication systems put strict requirements on the cables in order to simplify their end-points. That's probably a good idea when you don't have restrictions. Optical communications would be a good example of this.

BPL is on the other side of the trade-off options: we do not have control over what the medium looks like (powerlines are already there, you cannot replace them), so we need to put a lot of intelligence and complexity in the end-points. Because of this, the end-points have been designed to handle the worst possible channel conditions (high attenuation, significant reflections due to impedance mismatch, time-changing characteristics, strong non-white non-Gaussian noise, etc).

To put it simply, when somebody has control over the transmission media, it makes sense to put strict requirements on the media, so that the communication equipment can be made simpler or less expensive.

Going back to Ed's remarks:

I attended a presentation given by Ron Hranac, a member of the Society of Cable Communications Engineers Board of Directors. Hranac outlined the improvements that need to be made to a well-maintained cable plant to make it work reliabily for broadband use. Things like the phase characteristics and gain flatness of the system need to be closely controlled. The idea that all that really isn't needed, and that one can just put those signals onto any old wire, is not technically supportable.