David: Let's start by being quite general. From your perspective, do the claims of the ARRL have any merit at all? If so, what? If not, why not?

Glenn: Yes, I think they do. I think that there is no question that HF-BPL systems, which are forced to share spectrum and unintentionally radiate due to the physics of the transport they use, can and will interact with licensed users of the HF spectrum. From what I can tell, the ARRL has made some of the more thorough and careful investigations of the nature and degree of this interaction, both as to system egress -- interference due to BPL radiation, and ingress -- the BPL system's sensitivity to licensed radio users in the same frequency ranges.

David: Detractors claim that the radio frequency band used by BPL is quite subject to interference by simple consumer devices like baby monitors. I would think that a broadband service that can be easily cut off is a bad thing. So, is the claim true from your perspective? How reliable is BPL service and what is the risk of the service stopping?

Glenn: My opinion is that simple consumer devices and unintentional radiators will have very little impact on HF-BPL systems, particularly as compared to the effect of much higher power licensed radio transmitters in the HF spectrum.

A computer or other information device connection to the Internet, a very complex worldwide system, is subject to many types of failure, from a crash of the local device's operating system to a failure anywhere along the way.

However, beyond the user level, there is generally a significant amount of redundancy and provision for failures. From what I've seen of HF-BPL systems, I'd not expect failures due to the portion of the system they would have to dominate. There are almost always problems as new technologies are brought to market, but I see no reason to believe that BPL should be significantly better or worse than other elements of the system.

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?

Glenn: It appears to me that the biggest risk of interference occurs fairly close to the power lines to users who are trying to receive a weak signal on a (un-notched) frequency that a HF-BPL system is using. This generally includes only frequencies in the 4-48 MHz range.

Even those systems reported to interfere the most appear to drop off as one gets a mile or more away. While there may be some situations where one of the licensed users you mention experience interference at greater distances, I wouldn't expect that to be common. I should also point out that it is still too early to tell what will happen if and when a very large number of BPL systems are deployed and can collectively contribute to interference at large distances. It's a very difficult problem to analyze and I don't think the results on that one are in yet.