Cable-modems are designed to work with cable plants that must satisfy certain characteristics. If the cable network is not well maintained, the effects that Ed mentions can happen (phase distortion, frequency-selective channel frequency response, etc), and most cable modems are not designed to handle it (because that would add extra cost for equalizers, etc).

In the case of BPL technology, we know for sure that most cables will introduce severe phase distortion, non-flat channel frequency response, non-gaussian noise, and a lot of other interesting effects (interesting from the engineering point of view, that is) so the system is already designed to handle it. BPL systems require a lot of complex DSP (Digital Signal Processing) in order to correctly demodulate signals that have been distorted by the medium.

Improvements in DSP technology have allowed BPL technology to reach the performance and reliability that we enjoy today.

David: When I spoke to you during your vacation, you told me that what the ARRL is complaining about was an older implementation of BPL. Can you elaborate on this?

Chano: This is related to my previous statement about first generation versus second generation BPL technology. Our second generation BPL technology, introduced in 2003, provides much better interference avoidance techniques than our first generation system. Our second generation system is capable of introducing notches in ham radio bands (and also other frequencies) with a depth of up to 40dB, which is 10 to 15dB better than BPL systems from other vendors.

You can see ARRL's view of DS2's second generation technology at http://www.arrl.org/news/stories/2006/03/22/1.

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.

Chano: I'm not an expert on military communication, so I cannot really give an informed opinion here. However, DS2 second generation BPL chipsets use frequencies below 34MHz, so there should be no problems there. I cannot give an opinion on other BPL systems that may use different frequencies.

In any case, as an engineer I would be surprised if a well-designed modern military communication system, that included the latest spread-spectrum anti-jamming techniques, could be interfered by a BPL service. But again, I'm not an expert on that area.

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?

Chano: As I have mentioned before, I think the problem is that many people had a bad experience with older versions of powerline technology, which were based on non-OFDM (Orthogonal Frequency-Division Multiplexing) modulation schemes.