PLNs
I'm a radio amateur and CB user, and a few weeks ago I called on Ofcom to come and investigate interference I was experiencing from PLN. The chap came over and quickly traced it to a BT Vision installation a few houses away. Fortunately the householder is happy for BT to replace the PLN gear with a cable. So in my case I can happily use my gear for a little longer... until someone else nearby gets BT Vision.
The amount of interference that these devices cause over the HF radio spectrum (30MHz and down) is just incredible, and potentially very damaging. Please don't assume it's just a bunch of nerdy radio anoraks like me who are going to have an issue with PLN; there are many, many other licensed services that use portions of the HF spectrum, including of course world broadcasts, marine, and aviation.
PLN has come about because Ethernet cables and 2.4GHz wireless equipment are more expensive and time-consuming to install. This is why BT use them in thousands of BT Vision installations. But how on earth can we justify this cost saving at the expense of obliterating the HF radio spectrum and making it useless to other services? As PLN becomes more widespread, unfortunately that's just what's going to happen.
Incredibly, these things have been allowed to go on sale without being subject to licensing or regulation because they're not 'considered' radio broadcast equipment. Unfortunately, electronic equipment obeys the laws of *physics*, not *bureaucracy*; if you're going to inject very strong broadband RF into the unbalanced tangle that is your house wiring, then presto - you have a bloody efficient and damaging HF wideband radio transmitter, end of story. (And no, the RF does *not* "stop at the fusebox", as some PLN manufacturers incredulously claim.)
Ofcom says that the number of complains has declined recently. Hmm... could this 'decline' actually be more attributed to the fact that complaints regarding interference to SW broadcasts stations has now been offloaded onto the BBC? I'm glad I made my complaint anyway, and notched the statistic up by one!
The article mentions the possibility of interference to ADSL. Going back to my case of PLN interference, I noticed that RF was being particularly strongly re-radiated from the BT line to my house (expected really, as we all have overhead lines from the same pole). I also saw that downstream margin reported by my ADSL router improved by about 1 or 2dB when the neighbour switched off the PLN equipment. Not very significant I know, but it demonstrated to me that even existing broadband equipment (which sits at the very low end of the HF spectrum) can be affected by PLN, too. This is why it's frustrating when I hear PLN users claim it's only a small group of radio anoraks that will be affected. RF works in mysterious ways, and all equipment such as your ADSL gear that uses RF has a level of susceptibility; and the more devices you have sitting in houses spewing out strong RF, the more you'll notice services and equipment that you enjoy and depend on being affected. Even if it's playing MW2 online!
Biting the hand that feeds IT
