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, if not, help us understand where the ARRL's claims may be wrong.

Glenn: As I said earlier, I think that the ARRL has done a good job in providing credible and objective reporting on the HF-BPL systems it has investigated.

I believe that Ed's comment is very much in line with the description I previously gave of the differences between E-Line and HF-BPL technology. Once the dimensions of a balanced or wire-against-ground transmission line get large compared to a wavelength of the frequency being applied, it stops operating as a transmission lines and starts to operate as an antenna.

HF-BPL is definitely trying to function in a transition region for this type of transmission line and this is what limits the higher frequency operation. Although the FCC has considered the frequency range up to 80 MHz to be BPL, I don't know of any company that is trying to use the lines above 48 MHz. Basic physics prevents them from being used effectively in this way at much higher frequencies.

David: One of our readers, a very credible Lieutenant Colonel and a veteran of 24 years service with the US Army Signal Corps and two wars, tells us that "BPL will adversely affect military tactical communications since the standard FM radios (35mhz to 75 MHz) used by the Army and Marines are well within the BPL spectrum." This seems pretty worrisome. Can you comment on his concerns?

Glenn: Here again, I think it remains to be seen. If HF-BPL deployments continue in the same manner as the trials, I wouldn't expect the region above about 48 MHz to be affected. If the frequency range your reader quotes is accurate, I would only expect even the potential for interference to occur between 35-48 MHz.

Whether interference is actually experienced would likely depend upon how marginal the communications was to begin with, that is, how weak the signal to be received was, and how close to the BPL lines the military radio was positioned.

David: We are hearing from some extremely credible experts who are going "full goose bozo" against BPL. Usually when there's such a fuss about something, especially when credible experts are strongly opposed, there's some foundation in fact. If these experts are wrong, why? What are they missing? And could they possibly be right?

Glenn: Well, you're probably correct that when sincere people are holding extreme and opposite views that the actuality is somewhere in between. But while some may have labeled the ARRL as being in the extremist camp, I personally think that they have come to adopt quite a reasonable position.

For one thing, they have indicated repeatedly that they are not against BPL but rather, against interference caused by BPL. Also, they have offered to cooperate with all BPL vendors in resolving the interference issues and seem to have done so, with good result, in some cases.