For the past four or five years, the promise of broadband over power lines (BPL in the US, PLC over here) has been bubbling away. Various technical tests have proved that it's feasible, but the commercial side is less clear. Now, a paid-for trial is underway in the ancient city of Winchester -- and if it works, then there'll be another broadband delivery mechanism. That has to be good, right?
Er, no. PLC works by squirting lots of radio frequencies carrying data down the power lines, so in that sense it's much the same as ADSL and cable. But whereas the latter two are relatively low power, well characterised and usually underground, the power line signals have to be much beefier. They have to contend with an electrical environment with tons of powerful noise floating around, and one where the bits were never designed to carry data. So, you end up pushing quite a lot of radio-frequency power through lines suspended in the air. Hold on, isn't that how you broadcast radio signals?
Er, yes. PLC has the potential to -- and has been demonstrated to - blot out huge ranges of shortwave frequencies, over quite some distance. Now, you may not care tuppence about this: you probably don't sit there of an evening listening to Radio Pyongyang fading in and out of the ionosphere. Those who do, are very worried --- and licensed radio hams, who stand to lose the use of huge amounts of their legally allocated spectrum, are bordering on furious.
Hey, who cares about radio hams? Outdated hobby. Tony Hancock. Strange old men with a peculiar fondness for black rubber helical aerials. Well, ask most of the eastern US, where last weekend the hams turned out nearly instantly to pass thousands of emergency messages as mobile phone base stations, police repeaters and other bits of official infrastructure gave up and fell over.
On the other side of the bat, radio hams are also very capable of transmitting huge amounts of power, which will do PLC's bandwidth no good whatsoever. If the frequencies are so jammed that nothing less than hundreds of watts will get through, then that's exactly what the amateurs will be forced to do.
This could get very messy.