Original URL: http://www.theregister.co.uk/2011/05/17/gchq_plt/
GCHQ man: Powerline networks do interfere with radio
Spook not a beardy radio ham, but is moustachioed
D Notice A document prepared by the spectrum manager of secret UK listening agency GCHQ, though disavowed by the organisation, has drawn more attention to the interference kicked out by powerline networking kit.
The letter was prepared by [a government employee we have been asked not to name], of government-spy outfit GCHQ, and suggests that powerline networking kit is already interfering with GCHQ's clandestine listening operations. But, after being leaked to the radio-ham community in March, the letter was officially renounced by the organisation as never being an official document and containing various inaccuracies.
The letter was prepared in May, leaked in March, and posted on the Ban PLT web site. At first glance it appears quite damning, stating that GCHQ is "already measuring an increase in the HF noise floor in the vicinity of our HF receiving stations, with wide variations between day time and night time levels", though it goes on to state that seasonal and meteorological factors also impact signal strengths.
If power line networking is causing headaches for our spies then that's a serious issue, and PLT kit certainly operates right in the bands used by the Numbers Stations.
Numbers Stations are mysterious radio broadcasts that have been around since the 1950s. They transmit what appear to be random numbers, spoken aloud, and are assumed to be broadcast instructions for operating spies. The stations are plainly important to the UK intelligence services in their own right, and there are other uses of long-range HF that GCHQ needs to listen in on: HF is still commonly used in naval communications, for instance, even if it no longer carries much international phone traffic.
So it would appear that it's not just the bearded-radio-ham community which objects to PLT, except that [the person we have been asked not to name] is a fully-paid up member of that community. He doesn't have a beard, just a moustache, but he is a keen radio amateur as well as working for GCHQ.
That doesn't invalidate his opinion, as expressed in the letter, but in distancing itself from that opinion GCHQ has stated that PLT kit isn't impacting its operations. It is possible that GCHQ is lying, one should expect a certain amount of deception from one's spies, but it's more likely the organisation places its listening stations well away from anywhere people might be using power line kit.
The subject of PLT interference will get into the houses of Parliament again on Wednesday as Mark Lancaster, MP for Milton Keynes North, has raised it as an adjournment debate (a 30-minute conversation) following a request from one of his (radio ham) constituents.
Which is another way that the ham community is fighting hard to raise the profile of interference generated by PLT kit, while the regulator (Ofcom) still denies there is any interference  and points out that it couldn’t do anything even if there was.
Most end users of radio, just trying to get their fix of Chris Evans in the morning, will just buy a bigger aerial, or complain that DAB isn't as good as FM used to be, never knowing that it's their home networking kit which is causing the problems: unless the hams keep telling them. ®
Updated to Add
Having been contacted by a GCHQ representative under the provisions of the DA Notice system  (formerly D-Notice) we have removed the name of the GCHQ spook in question and are no longer linking to the document. Not everyone is as patriotic as us, though, so if you're interested you can almost certainly find out both.