back to article 'Interfering' BT Vision attracts campaigner glares

Campaigners complaining about interference generated by BT's Vision product have financed independent tests to show that the kit BT is pushing fails to conform to the appropriate EU standards, prompting a complaint to trading standards officers. Shortwave radio users have been complaining for a while about interference …


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  1. Michael Fremlins

    This is BT you're talking about

    They have the power to get the law changed so it doesn't affect them.

    Don't count on a recall of all the devices that have been sold.

  2. Anonymous Coward

    ..ensures goods bear the appropriate marks

    I'll be offering them a rolex from china then!

  3. Anonymous Coward
    Anonymous Coward

    Will be interesting to see what Offcom does next

    Equipment isn't supposed to emit interference, it clearly does, and it's up to Offcom to enforce the law. The longer they dither, the more kit that gets installed...

    Offcom's good at dithering.

  4. jason
    Thumb Down

    Sounds like a brand slogan.......

    'Ofcom - Poweless to Act!'

    Almost as nifty as Tesco's.

  5. Anonymous Coward

    Vulnerable to sniffing?

    If this is causing interference, it follows that any unencrypted traffic is going to be vulnerable to passive sniffing from a distance via RF scanners.

  6. Thomas


    I think most powerline ethernet thingies apply encryption - there's certainly a relevant standard and at least one of the major brands comes with the feature to automatically propagate an encryption key if you have physical access to the plugs.

    Hopefully it's more secure than WEP was...

  7. Brian Whittle

    home hub

    There is supposed to be a problem with BT Homehubs interfering with shortwave / sideband transmissions according to a one of my radio geek friends

  8. Adam Salisbury
    Thumb Down


    Office of Failed COMtards

  9. Dave


    Are quick enough to pounce if a licenced amateur causes TV interference, but it appears that companies are exempt.

    No change there then

  10. Alan

    Ofcom will do nothing

    Analogue radio is going to be shut down in a few years, why would they bother doing anything about interference to reception of it. As long as DAB is not affected they will be happy.

    Of course there are many radio hams (myself included) that will not agree with this -- I often listen to short wave broadcasts and would be very annoyed if I was prevented from doing so due to "legal" interference. At the moment there is no problem in my area as BT can't even provide broadband let alone vision!

  11. Joshua Murray
    Paris Hilton

    I've had this issue...

    I was a "victim" of this issue and logged a complaint with Ofcom.

    However, before the field agent was scheduled to visit, my neighbour agreed to remove the devices from his home, for which I am very grateful!

    If you are a radio amateur, enjoy listening to shortwave broadcasts, or are a scanning enthusiast, a neighbour getting a pair of Comtrend PLT devices means it's very likely that you will be unable to hear anything apart from this digital noise on most of the HF spectrum.

    They need legislating against, soon!

    /Paris, because she might enjoy being interfered with.

  12. Anonymous Coward
    Dead Vulture

    Ham Radio

    Yes and let's have people walking with red flags in front of our cars.


  13. Anonymous Coward
    Anonymous Coward


    in theory the equipment itself isn't outputing any interference, the mains cables are, i bet this will be the argument that is used, (as its in theory correct)

  14. Anonymous Coward
    Anonymous Coward

    Oh you mean....

    .....just like their (allegedly) overpowered home hub wireless routers which are alleged to be transmitting with too much power, hence their claim of having a "greater range" in their adverts?

    Of course, BT would never do anything unscrupulous like that......or Phorm.....

  15. Peter Kay

    Sniffing - not vulnerable

    All traffic has the option for 128bit AES encryption so, no, it shouldn't be vulnerable.

    Personally I love the homeplug kit - it's easily one of the most effective and least hassle devices I have.

    Although I have some (extremely small amount of) sympathy for the shortwave radio enthusiasts they don't help their cause by making stupid arguments like 'it might interfere with military transmissions'. I'm sure that'll be a huge problem, if there's ever a chinook 200m from my house..

  16. Tom


    I hope they don't pull these as the HomePlugs I've bought are probably the most reliable networking means I've found in a good while. Wireless is crap.

  17. Hedley Phillips

    At last

    This equipment has been causing interference on my CB and is very annoying. Unfortunately there is nothing we can do as CB users as we don't pay for a licence, therefore we can't complain to OFCOM (as far as I know).

    Well done HAM users. Lets see whether the toothless giant that is OFCOM can do battle with BT and win.

    nope, never mind.

  18. Chris Judd

    Not actually BT Vision that's at fault...

    The article seems to imply that the device causing the problem here isn't the Vision box, it's the Powerline adapters. These are just 3rd party branded devices, not really BTs responsibility. They'll just switch vendor and carry on regardless. The problem was probably that BT went with the cheapest adapters they could find, rather than decent quality ones.

  19. Richard


    Many short wave broadcasters are moving across to using Digital Radio Mondale. This will make using short wave as easy as using DAB, so should help attract a new audience. PLT interference has the potential to threaten the future of DRM.

  20. GrahamT

    If it's not FM then it doesn't count

    My wife used to listen to French radio on Long Wave until terrible interference made it impossible to listen to. When we researched how we could get BT/Offcom to investigate and stop the interference we discovered that they will only take action if the interference affects FM radio transmissions.

    As Short wave transmissions are AM/SSB then I don't think they stand a chance of getting anything done, especially as Offcom use BT to do the technical investigation work.

  21. Anonymous Coward

    Legal PLT effectively impossible anyway

    The tests carried out in EMC test houses show that the un-notched signals are about 28-30dB above the EN55022 Class B limits. The modulation format used is OFDM, the necessary signal:noise ratio to get acceptable error rates is about 20-25dB. This suggests that if a PLT transceiver has its output power reduced so that it meets EN55022, the signal:noise ratio would be down to well below the noise level, resulting in no comms at all.

    You can see why the PLT companies don't want this explored further, and recently they were prevented from pushing through a change to the standard in the CISPR 22 committee that would have increased the mains test network defined LCL from 6dB to 24dB (that's essentially saying that mains wiring is much better balanced than reality. As a comparison, CAT5 cable has an LCL of 60dB, so is very well balanced, which is why Ethernet cables don't radiate much at all. It is the unbalance in the mains wiring that causes the RF to be radiated, you can't make balanced mains because of the number of spurs, light switches and the variable termination due to the wide variety of mains-powered equipment.

    There is one more aspect to this. If a manufacturer can't get a piece of kit passed by a test house, they can use the Technical Construction File route. The TCF is essentially a report that details how a piece of equipment is built in order to pass (whether it actually does or not), one then can self-certify and never actually submit the equipment for testing. Once this is done, the CE mark can be applied and you can sell the kit it in any EU country. No country can then legally remove it from the market without a lot of effort and expense (EMC testing costs thousands of pounds for a couple of days in the test house) and there is no mechanism to revoke the CE mark where a TCF is created.

    Radio amateurs are particularly vulnerable because they often operate with signals that are very weak, unlike broadcast stations which try to deliver a high enough signal level to overcome at least some local noise. That's why the PLT devices have notches in the HF amateur bands, but they are not really deep enough for a complete cure. Short wave listeners are trying to receive at frequencies where there are no notches, in many cases the PLT interference (which can be heard over at least 500m in lots of installations) is too great and they cannot receive any more.

    Remember the the ionosphere only works for radio propagation over the 3-30MHz range, there are no other frequencies that can be moved to.

    Essentially the regulators have dropped the ball over this one, with a bit of luck the chickens are going to come home to roost and the PLT manufacturers are going to find some chill winds blowing.

  22. Andy ORourke

    Is it the box....

    ...or the house which is emitting the interference? I mean if the box is designed and implimented to EU standards regarding interference / emissions but the mains cabling in use in the property is causing the problems then BT and the manufacturers are home and dry aren't they?

    Not saying it is right or fair but if the box isn't the root of the interference then it must be the person operating the box who is at fault yes?

  23. Shane Mussell

    OFCOM = Business leaders after work party

    OFCOM are useless..

    As for us HAM's well.. As we may be about to lose 70cms (airwave) and are seen as old men in tweed jackets moaning about young peoples motorbikes causing interference with our valve radio, chances of anything good happening/coming out of this.. Nill.

    I'm looking forward to the OFCOM ruling that tells HAMS to encrypt radio transmissions to save the spectrum... lol..

    Sometimes I wish I worked for one of these organisations, then again would I be able to live with myself doing what they do?

  24. Elmer Phud

    Noises off

    The BT Vision kit was so noisy locally on the mains that my old hi-fi amp was almost unusable. Changing the network bricks helped and buying a mains filter extension lead (for audio, the other type were useless) has pretty much cured it. Bit of an expense for getting a free box.

    The network bricks were a revelation though, can't see much point at home for wireless now. And the Vision box works well. Swings and rooundabouts, I suppose.

  25. Peter

    Interferance works both ways right?

    If they are "legal" to broadcast on that frequency or ofcom is "Poweless to Act" on this then surely it is possible to just generate noise at the appropriate frequencies to stop this kit from working?

  26. Alex
    Thumb Down

    its all a bit "Keith Harris & Busby"

    I can't help but think that BT seem to have their hands up the backside of too many gov depts.

  27. Neil

    Interferance to other users

    I'm interested if the PLT that the Comtrend unit uses (for better or worse) would have an effect on other users of PLT for data.

    It certainly SOUNDS to be fairly constant traffic from the video clip.

    Incidentally, the interference doesn't seem limited to the amateur bands - the video shows it affecting the internationally agreed 13m shortwave broadcast band which does have some users as its the longest range band not seriously affected by the sunspot cycle.

    I hope Ofcom will make them sort it out!

  28. Chronos


    Yes, even if the TV is a Dixons special, their feeder is forty years old and effectively a full line of point contact diodes, the aerial is composed mainly of aluminium [1] oxide and some idiot has installed a wideband preamp with a dynamic range in single figures. As you say, business as usual.

    The question remains whether there is still anything on the amateur bands worth protecting, though.

    [1] Oi! Mozilla! Screw your bloody half-arsed dictionary.

  29. Anonymous Coward
    Thumb Down


    The number of official complainants was over 60 several weeks ago.

    Only a fraction of BT Vision installations will be using these dreadful PLT devices.

    A superior connection is always obtained by direct wiring,will save a bit of power

    and avoid the BT customers being in breach of the non interference condition of

    their TV licenses.

    These units are normally left powered 24/7 and generate interference even when

    the tv is off and the standby button of the PLTs is pressed.

    I complained to Ofcom and after several months 4 pairs of units were removed.

    3 were direct wired, the fourth was changed to WiFi.

    All these BT Vision customers are getting good TV and my severe interference

    problem has gone away.

    I was affected by a fifth installation that went off for reasons unknown.

    Weak intereference can still be heard from PLTs over 250 yards away.

  30. Anonymous Coward

    Sniff what exactly?

    Its a frigging TV box why bother?

  31. Irate BT User

    Digital transmissions are also affected by Interference!

    Some common Symptoms of Radio Interference on Digital Equipment are "unwanted equipment lockup", "dropouts", "system reboots!" or "failure to connect to Service".

    When more of the Radio Spectrum is used for Digital it will become more apparent in the same way that "TV Interference" was never expected to happen on the then new uhf 625 line system!

    Conclusion Industry must keep it's equipments Radio Spectrums within the Alloted Radio Bandwidth!

  32. Anonymous Coward
    Anonymous Coward

    Why bother about shortwave?

    Shortwave's days are clearly numbered so I doubt Ofcom will see any advantage in chasing this one.

    @Chris Judd - I think that your friend may be confusing the home hub with the PLTs.

  33. John Murgatroyd


    I feel sure that some public servant , currently working for ofcom, will soon be enlisted as an executive director or something. Probably more than one.

    OFCOM, specialists in CASHmunications.

    Motto: If we can get something for it, we'll sell it, to anyone.

  34. Peter Kay

    'just a frigging TV box'

    Read the article again. This is to do with BT being one of the largest users of homeplug/powerline networking devices. The devices are ethernet bridges and you can plug any ethernet device into each end. BT will use devices at the cheaper end of the market, and these may well not be as accommodating to the spectrum used by shortwave radio.

    In comparison to wireless adapters they're faster, more reliable and easier to use (unless you need to move the computer regularly to where there isn't a power socket ;) ).

    Whilst I'm sure in the BT scenario it's simply a cost of support issue, anyone else explicitly buying a homeplug device usually has a good reason to do so. Wireless just isn't as good, and if it was simple to wire up the premise the person obviously would have done so - in newer houses it is an utter arse to try and fit network cables between different floors. There are huge floor grade chipboard 'floorboards'. the wall cavities are completely full and there is no floo. So either it has to go through the loft (may not be possible), around the outside of the house, tacked/stapled unattractively to a *lot* of walls, or replacing a load of skirting board.

    Given those options, spending 50 quid and less than five minutes on something that just works and carries on working is very attractive.

  35. Richard
    Thumb Down

    Re: AC Luddites

    When the Twin Towers collapsed, emergency comms went off-air, because the infrastructure equipment was on top of the buildings. Radio Hams from many states came in to support the relief effor and set up networks to route messages between emergency services and also for the Red Cross.

    During the Boxing Day Tsunami, relief efforts were also assisted by Amateurs using Short Wave communications. Amateur radio is part of a great many disaster recovery plans worldwide.

    You can call us luddites if you want, but in crisis situations, damn useful luddites to have arround.

    --... ...-- / -.. . / -- ----- ... -. .-.

  36. Anonymous Coward


    No surprise you had to post as AC old man. It isn't being a Luddite to expect interference limits to be respected, otherwise none of your shiny kit would work at all.These limits are relatively recent requirements, and have been drawn up because as newer systems have evolved it has been necessary to ensure that the EMC problems resulting have been kept under control.

    PLT is one of those "because we can" technologies, and has driven a coach and horses through other people's allocations. It's only because of blatant manipulation of the regulatory process that this could occur, it was obvious to many of us that allowing self-certification for EMC testing would lead to trouble.

    BTW, this works both ways, 400W PEP of HF SSB transmitted perfectly legally will usually cause a PLT system to fall over, funnily enough the pickup is caused by the unbalanced nature of the mains wiring that the PLT companies don't care about. What they sow, they shall reap!

  37. Simon


    That's one hell of an oversight! I didn't expect to see that amount of bandwidth obliterated by that signal, but there it is. Makes one wonder how many other systems are being disrupted by this and they haven't clued into the source of the problem.

  38. James Hughes

    DTV interference

    Can stuff like this cause interference on DTV (i.e. Freeview)? My two tellies have started getting occasional dropouts for no apparent reason, (signal drops from 70% to 10% for about 1s) so was wondering where the interference may be coming from - could it be something like this? I have even had weird traffic on my car radio next to the house - like a police broadcast over radio 4.

    We must be told!!!

  39. Paul Widger
    Thumb Down


    Graham T

    You are now entitled to interference free radio reception.

    This is covered by EMC regulations 2006.

    First make sure the noise isnt coming from your own house.

    Listen to the station on a battery operated set,then switch your

    electricity off at the main switch (on or near the fuse box) if the

    noise stops it is something in your house!

    If not Complain to Ofcom.

    Ofcom DO NOT use BT to do interference investigation.

    BT stopped doing this many years ago.

    Legal licenced CB users.

    You are entitled to reception free of PLT noise.

    It does not matter that you no longer have to pay a fee.

    Complain to Ofcom.

    Best regards.

  40. Anonymous Coward

    Sorry guys, you're out of luck...

    I'm afraid these gadgets are just far too useful to live without - I can't get decent consistent bandwidth to my living room over WiFi (possibly as a result of the fact that last time I ran a scan there were something like a dozen access points visible from my home, and that's only going to get worse...) but I've got a BT Vision box, an XBox, and a Wii happily sharing a single Comtrend 200 MBit ethernet-over-mains box through a single router. Moving the router's not an option because that's plugged into an old fashioned fixed "engineer installed" filter box in the office (where the bulk of the kit which needs to be plugged into it is anyway). Running CAT-5 around the place is a complete non-starter because my wife objects to exposed wiring and I'm buggered if I'm going to redecorate half the house to hide it.

    I'm off to EBay right now to pick up a couple of extra boxes to go in the kids bedrooms and replace the (fiddly to configure and poorly performing) D-Link WiFi bridges while i still can...

  41. raving angry loony


    I thought Ofcom had been purchased by BT Marketing Plc years ago? Aren't they now part of BT's "conformance marketing" division, charged with making sure that anyone who complains about BT quietly disappears?

  42. Anonymous Coward
    Anonymous Coward

    BT - What --- Never

    Nah, can't be true. BT are one of the finest and most reputable communication companies in the world.

    What's that you say. it is not 1989 and I have been in a coma for 20 years!

    Wow your right, after further investigation I can now see that BT are a load of *&%^$$%*((*(

    What's all this Crap called BT Webwise?

  43. Alan

    @ Richard

    DRM (Digital Radio Mondale) won't work if interference levels are high either, this stuff will probably mean the end of long distance radio as Ofcom certainly won't take an interest in short wave listening either digital or analogue. The only time they will investigate is if you cannot receive TV or DAB as that's what your licence entitles you to receive, nothing else matters.

    Funnily enough I have had to try for ages to send this as my 3G internet connection has given up -- it seems to get very unreliable about this time of day--- interference problem? unfortunately I can't get wired broadband -- exchange oversubscribed apparently

    One hour later -- still no-go ---- trying again one an' a half hour later -- let's see

  44. Anonymous Coward

    At AC Out of Luck???


    So do you mind if I sit outside your house chatting on 433.920MHz with a mate locally and swamp your car remote control plipper so that your remote control doesn't work?

    Or if I ignore your bleats of complaints because YOUR TV or whatever doesn't comply with CE immunity legislation, and transmit 24/7, so your Tellybox is totally wiped out?

    My radio's are "too useful to live without" and cost way over an order of magnitude more that your "gadgets". Your PLT is illegal, my equipment is legal. PLT products do not comply with EMC Essential Requirements. It is inherent in the design. We have demonstrated that. Why do you think that Comtrend have not replied to El Reg? Why do you put your convenience over other peoples?

    They know they are in the wrong. They claim to comply with specifications that they simply do not.

    If my name was Harold Fitch, the chap that signed the Declaration of Conformity for the Comtrend DH10PF, my arse ring would be twittering now.

  45. Herby

    Simple Solution...

    Just run a wire from Point A to Point B. Look it is pretty cheap to do (cost less then the BT Vision Kit!) and if you can't run the wires then TOO BAD!

    When the complaints come from the Military Radio people when a terrorist attach happens, they MIGHT listen. We can only hope so.

    Of course, the fallback position is two tin cans and a string. Works quite well. Could even be considered "wireless" (but not "stringless").

  46. Anonymous Coward
    Anonymous Coward

    @At AC Out of Luck???

    "My radio's are "too useful to live without""

    No they're not.

  47. Radiosgalore

    Uphill battle

    I fear it will be an uphill battle to sort this mess. BT are so big Ofcom would have a massive job trying to correct this mess. Not that they shouldn't mind it will just be very hard

  48. Cortland Richmond

    No intereference here. Move along, please!

    One would think that radio interference meeting the Wireless Act's definition must be stopped regardless of certifications on offending equipment. However, if one owns the police force, what gets stopped may be negotiable with the highest bidders.

  49. Anonymous Coward
    Anonymous Coward

    @Shane Mussell

    'Old men in tweed jackets'

    When did radio amateurs get an image makeover?

    Sorry to burst your bubble but the image most people have of hams is of a sweaty, fat, pipe smoking old man with a personal hygiene problem and NHS glasses held together with sticking plaster.

    Of course there may be tweed involved but only because it was cheap at the local church fete jumble sale.

  50. Lionel Baden

    ask first

    If my neighbour asked me to remove the plugs i would.

    Unless its the wanker from upstairs he can go suffer !!!

    but yeah it never hurts to ask,

  51. Anonymous Coward
    Anonymous Coward

    @Clint Sharp

    I think you'll find most people don't have an image of a ham radio operator becouse most poeple don't know what one is.

    However they do posses very useful skills and equipment and it would be a huge loss if they were to become extinct becouse a bunch of inbreds couldn't live without connecting their toaster to the internets.

  52. Martin Silver badge

    WHY would anyone use the powerline for communications?

    I have precisely NO sympathy with the people who are saying 'I don't want to be arsed to run CAT5.'.. Then you can't be arsed to have a service, bye bye now, failures.

  53. Jonathon Green

    @Uphill battle

    "I fear it will be an uphill battle to sort this mess. BT are so big Ofcom would have a massive job trying to correct this mess."

    I think it would be a mistake to assume it's just BT you're dealing with here...

    BT may have put a significant number of these things in the field by bundling them with the BT Vision box but they'd been gaining popularity for quite some time before that and there are a *lot* of them out there. Take a look in your local PC World and you'll see a fair size display of Powerline Networking kit from a number of different manufacturers (if my understanding of the situation is correct the problem is inherent to the technology rather than specific to the Comtrend units BT are supplying) and I know of about half-a-dozen (non BT Vision) installations which have happened purely as a result of my own enthusiastic championing of them, you'll also find enthusiastic reviews right here on El Reg (e.g. which I'm sure will have shifted a fair few units.

    In the light of this Ofcom's estimate of about 500,000 units may well turn out to be highly conservative if they're just going by BT Vision installations and that's potentially going to mean a *lot* of extremely hacked off customers and a lot of people banging on the doors of BT, suppliers, Trading Standards, small claims courts, etc, etc if it turns out that they've been sold kit which they can't use and has been mis-described in the form of invalid CE certification. In turn that will possibly mean a lot of small businesses (I'm thinking of small business IT consultancies, people supplying networking kit and support to home users, etc, etc, etc) who've acted in good faith by supplying properly marked kit from reputable manufacturers, bearing the correct certifications caught in the middle of a fight not of their making.



  54. Anonymous Coward
    Anonymous Coward

    @AC "you mean..."

    The home hubs are not overpowered. The "greater range" advertising hinges (if you read the small print) on the fact that the home hub is 802.11n and they are comparing it to rivals' 802.11g devices. It's just the usual advertising lies, nothing to do with the power output at all.

    Check your facts before posting.

  55. Anonymous Coward
    Anonymous Coward

    @AC "Sorry guys, you're out of luck... "

    So you've never heard of CAT5 then?

  56. Anonymous Coward
    Anonymous Coward

    Why BT?

    The Comtrend devices are not manufactured by BT. BT merely supply them as so many other companies.

    If BT are to blame then so is every other company who supplies Comtrend PLTs, and indeed any other offending PLT kit.

    However the people who are really to blame in this case are Comtrend themselves, or more accurately their EU agent, and indeed any other manufacturers/importers of offending PLT kit.

    Oh hang on, I forgot this is The Register. Much better to post an anti BT (or Microsoft, or whoever else is out of favour at Vulture Towers) story than to post a story slamming some importer or manufacturer most readers have never heard of.

  57. Jonathon Green
    Thumb Down

    So you've never heard of CAT5 then?

    Ever heard of walls, floors, and houses which don't have extensive cable ducting and/or accessible floor/ceiling voids to run it through?

    If I ever have a house built (or remodeled) to my specifications it'll be flood-wired from wall to wall and floor to ceiling. In the meantime with WiFi becoming increasingly congested, not having the bandwidth and/or reliability for some applications, and not going through actual proper walls (as against plasterboard partitions) terribly well PLT is a practical, domestically acceptable, affordable, and very, very attractive solution for a lot of people.



  58. Richard

    Re: Why BT


    BT have been pushing Comtrend PLT devices despite complaints via Ofcom regarding interference over the last 12 months or so. BT are aware of the problem, yet continue with the sale of the products. BT have also been responsible for the majority of PLT products deployed.

    WTF haven't they done due dilligence testing of their own and confirmed whether or not the products conform? They have a lot more resources than the UKQRM group at their disposal.

    We have heard spurious reasons for interference including QA issues and "dodgy wiring" cited as reasons for interference which is just plain and utter bullshit.

  59. Anonymous Coward
    Anonymous Coward

    @Jonathon Green

    I wired my old victorian pile for Cat5 with no problems that certainly was never designed for cabling. It had no wiring or plumbing when it was built and yet I had no problems putting the wiring in place.

    Under floor cabling? No problems house have these funny little things called floor boards. Inter floor cabling? Mains cabling, plumbing (including central heating), telephones and burglar alarms already have routes, all you need to do is track them down and follow them.

    There's hardly a house in the country that couldn't be cabled with minimal disruption. Hell you can even buy flat twisted pair for use under carpets. Perhaps if you live in a grade 1 listed property you might have problems with the wall boxes.

    That leaves the only real reason for using PLT devices being plain bone idleness.

  60. Anonymous Coward
    Anonymous Coward

    The Device or The Cabling?

    Is it the device or the cabling that generates the interference?

    A friend of mine had a baby monitor that sent it's signal down the mains and generated some serious interference. When he moved house he took the monitor with him, only to find that the interference problem had all but disappeared.

    Only anecdotal evidence I know, but some of the posts on here are a lot less than that.

  61. Anonymous Coward
    Anonymous Coward


    That still doesn't explain why BT are the sole target. Plenty of other companies are pushing Comtrend PLTs, they have exactly the same responsibilities. And it isn't just Comtrend that cause the interference. So the companies selling those also have the same responsibilities. That BT are aware of the complaints is irrelevant, no dount Comtrend are aware of them too, but they have done nothing either.

    You weaken your own case if you pick on a single offender. The defence that "everybody else does it" may carry no water when you get nicked for speeding, but I suspect that BT could build a robust defence around it if Ofcom did come a calling.

    Personally I wouldn't let a PLT anywhere near my mains, but that's mainly because the signal will crop up on next door's mains too. Yes you can talk up encryption, but bear in mind that it is mainly there so that a pair of devices can distinguish their signals from any other PLTs on the mains. I doubt the security of it is up to much. And of course you have no control of it, at least with your wireless network you have some control over the encrytption.

  62. John Murgatroyd

    Who cares ?


    Amateur radio is a licenced service.

    PLT isn't.

    So, no problems with complaints of interference to PLT.

    Even 100 watts on 80 metres guts the things.

    That's the problem with a device constructed to a financial immunity to strong signals.

  63. Anonymous Coward

    Consider this

    BT, will usually after Ofcom's investigation offer the user a wired solution.

    However if you get a nasty bit of work who won't budge then the case become more complex.

    The big thing thats annoyed many about BT is that despite being fully aware of this growing problem they chose to sign up to another long contract with Comtrend.

    This is probably for the Power Grid 902s which are if anything worse still!

    You are right to say there are other PLTs on the market but the Comtrend ones are by far the worst found so far.

    Other makes such as Advent, Netgear, Solwise etc also block out the radio spectrum with their noise!

    But Comtrend PLTs seem to transmit over vast distances!

    Currently I have one causing me trouble at 294 meters from me!

    I and other have also observed Comtrend interference at 500 meters.

    So its not a case of being intolerant or moving your antenna to get away from it.

  64. Anonymous Coward

    Consider this #2

    Also! its not inaccurate to call this a BT/Comtrend problem because the video is of a BT Comtrend system.

    Who else does Comtrend supply in the UK? anyone know.

  65. Cortland Richmond

    Balance? What balance?

    In Legal PLT effectively impossible anyway Brian Morrison said

    "You can see why the PLT companies don't want this explored further, and recently they were prevented from pushing through a change to the standard in the CISPR 22 committee that would have increased the mains test network defined LCL from 6dB to 24dB (that's essentially saying that mains wiring is much better balanced than reality."

    BPL in the USA often uses one-wire injection. In the original FCC RUlemaking, they asserted these would balanced feeds.

  66. UKQRM

    Consider this #3

    Hey sorry for posting anonymously last times, did not notice the tick was in place.

    OK, another interesting fact here.

    I have only tried this with Comtrend adaptors but there is no reason to assume it won't work with others.

    Time and time again various 'pro' plt groups say that these devices are not radio transmitters!

    Therefore they don't come under the same rules.

    So explain this then....

    If you take a set of Comtrend adaptors, plug one in your house and one in your neighbours house (assuming you live on a normal housing estate) you will find they connect up quite happily!

    The only way they can do this is if each device is picking up the transmitted 'radio' signals from the other.

    So what does that make them then?

    OK, there will be those who won't accept that, so what about Comtrends new power grid 902s that specifically allow for this near network pick up and agree on which part of the spectrum they will use?

    These things are radio transmitters, wide band and disruptive jammers.

    But it does not matter anyway as they have been shown to fail the required EMC regulations.

    They may be very convenient for the simpleton who can't run a cable or set up their wireless router, but the fact is they are (in mine and a number of others opinion) probably illegal.

    Have a look at this web link for a similar case that Ofcom has dealt with seemingly properly.

  67. Gareth Jones Silver badge

    @Consider this #2

    "Also! its not inaccurate to call this a BT/Comtrend problem because the video is of a BT Comtrend system."

    Right, here's a considered response: The video is absolutely nothing to do with Comtrend! Have you done no research at all?

    The video works perfectly well without the PLT devices. BT include a pair of Comtrend devices with each BT Vision STB just as a courtesy to customer's with a TV that is not conveniently near a phone socket. IOW the EU should only use the Comtrend devices if they can't manage without them, or are too lazy or stupid to run a few metres of cat 5.

    Of course it does make me wonder how much those two devices cost and how much the obvious alternative would have cost. You need a Homehub for BT Vision to work so a wireless connection would seem to be the obvious solution. It wouldn't be too hard to include a basic wireless adapter along with the necessary setup wizard to associate it with your home hub.

    I'd go for a wired solution. A 10m flat Cat5e patch cable specifically for under carpet use can be had for under a fiver. A perfectly acceptable solution when you consider that most houses seem to have at least one of coax, phone or burglar alarm cable already under the carpet. Quite why BT didn't include such a cable with the STB I don't know.

  68. John Murgatroyd

    Not really

    "If you take a set of Comtrend adaptors, plug one in your house and one in your neighbours house (assuming you live on a normal housing estate) you will find they connect up quite happily!"

    That will work for anyone on the same side of the local mains transformer. Even those streets away. The signal gets progressively attenuated but is still usable.

    I know it's bad practice, and seriously frowned upon, but using the mains earth as the signal (rf) earth from your tx/antenna tuning unit REALLY makes every day a bad day for these things. Given the low component count it is also likely that they would be damaged by the transmitted signal....minimal decoupling....and low-cost components.

  69. UKQRM

    @Consider this #2

    And you are saying I've not done my research at all?

    LOL I've done little else over the past year.

    No, sorry you misunderstood what I was saying.

    The video I was referring to was the video for this article.

    That is without any doubt Comtrend adaptors.

    Apart from that my dear fellow I 100% agree with what you have said.

    The cost of a easy to set up wireless router would seem a far better option for all concerned.

    Of course the other issue often overlooked is the extra power used by PLT systems! they get hot quite quickly so it must be a good few watts! not that green an idea either then apart from causing radio pollution far and wide as well of course.

    I have been surprised at the number of constructive comments here! must be a good readership.




  70. John Murgatroyd


    I was quite surprised at the results from the measurements on a Comtrend PG902 adaptor, in this months RadCom.

    40db over the noise floor ?

    That would wipe-out practically every signal in the spectrum affected. Even a station "down the road" would suffer serious interference.

    And in the case of the adaptors in which the notching can be removed, it would render reception of any signal from a few kilohertz to over 30 megahertz impossible.

    Apparently, the good news, the devices also suffer seriously from interference from strong transmitters.

  71. Anonymous Coward
    Anonymous Coward

    This message brought to you via PLT

    As taken from here:

    Powerline adaptors use less than 5w each, so assuming a pair is in use, that's 10w. Not so great, but do-able.

    I do realise that CAT-5 can be installed, however there's one key point here; permission. I'm living in a rented apartment, so I'm not allowed to touch the walls, floors or ceilings. We've got hardwood floors, so can't tuck anything under the carpets either.

    More importantly, I can currently see 19 wireless networks. I've tried all the available wireless channels, and found throughput to average around 10mbit, with ping times to the router hovering around 5msec, but spiking now and again due to retranssmisions. This is at a distance of 10 metres (through 2 walls) to the router.

    With powerline, the throughput is more on 60mbit, with constant pings of 1msec to my router. Browsing the web feels more snappy, online gaming enjoys lower pings, VoIP works better due to lower jitter, and there's sufficient bandwidth to stream high bitrate video to our HTPC via the network, rather than have to work on silencing the server.

    The best bit is, if we should relocate any of the devices, we simply need to be near a socket to have a network port. Or, if we move apartment, the network doesn't need to be rebuilt in the new digs.

    Sorry, but I'll stick with PLT thanks.

  72. Josie

    Storm In a Tea Cup

    As an ex BT engineer I came across this minor problem once. It was resolved by putting in a line extension to the Vision Box. The RF interference was much lower with the newer PLAs but I still put a line in. The customer in question used SW radio to listen to the World Service !!

    PLAs are a very good technology as they allow the use of cabled connection to the internet without the inconvenience and lack of flexibility that ethernet ports provide. Comtrends adaptors were the fastest on the market when they were introduced ie up to 200Mbps.

    I do not think that these PLAs should be banned or BT criticised for introducing them because a very tiny minority of its customers use SW radio or are HAM enthusiasts.

    There are very simple remedies to this problem outside of putting in ethernet ports.

    1. You could turn the PLAs off when you want to use your SW radio.

    2. You don't have to use PLAs or for that fact the vision box especially if you do not fritter your money on their VOD services.

    3. Go and buy another make of PLAs and sell the BT ones on Ebay or give them to someone who does not use SW Radio.

    I am bemused that some people think this is such a serious problem that they complain to OFCOM.

    Lateral thinking guys and lets face it SW radio is very very 20th Century. There are far more interesting ways to communicate now. As for the customer I dealt with he could listen to the world service on the internet!!

  73. UKQRM
    Thumb Down

    Storm In a Tea Cup

    It would be tempting to respond in a very angry manner as it looks on the face of it that you are simply ignoring the facts.

    As an engineer X or otherwise I have to credit you with a degree of technical understanding?

    This is not about just BT customers!

    This is about the person that lives upto 200 meters from the BT customer who finds his shortwave radio is being interfered with by the BT customer.

    You claim to be surprised that people have reported this to Ofcom!

    Well my friend, if you suddenly found you could no longer watch your TV I would imagine you would complain.

    Many hundreds of thousands of people still listen to shortwave radio and regard it as their primary hobby or entertainment.

    The shortwave equipment is ever more sophisticated with many new computer based radios.

    However, when you introduce a Comtrend adaptor to the neighbourhood, no matter how good your shortwave radio is, it can not function.

    And this is because the PLT does not comply with the required regulations.

    I am just about prepared to accept that BT was taken in by the CE mark etc but they now have more than enough evidence to show there is a serious problem and I would expect BT to conduct tests themselves or take note of those that have been done.

    PLT is totally antisocial, irresponsible and pointless.

    I accept that BT will step in and remove them when a problem is identified (in some cases) but when they fail to convince their customer to stop then it leave open just the Ofcom route or taking legal action against the user of the PLT.

    I can see this day getting very close.


  74. Paul Widger
    Thumb Down



    A) You cannot switch the PLAs off if they are not in your house but in my case up to 200 yards


    B) The householder who owns the PLAs may not be cooperative or flatly deny the have such

    a device in the home,this happened to me.

    Ofcom confirmed that I had correctly identified the houses.

    C) BT locally try to wriggle out of their responsibility to clear what Ofcom describe correctly as

    spectrum abuse,this happened to me.BT fed my neighbour a load of technical bullshit

    as to why "nothing could be done",of course being a retired radio frequency engineer

    I knew better and complained to BT headquarters.

    They soon changed their tune then and to be fair sorted the problem out fairly quickly.

    D) Have had to have 4 sets of these damned adaptors removed.

    Three were direct wired,one used WiFi.

    E) You are correct in saying you dont have to use the PLAs,an unknown fraction of BT

    Visions customers use them.

    F) If a listener thinks of changing the make of PLA to be used in their own house they

    will at best get a modest improvement.

  75. UKQRM
    Thumb Down

    Re: By Anonymous Coward

    By Anonymous Coward Posted Monday 19th January 2009 13:20 GMT

    As taken from here:

    Powerline adaptors use less than 5w each, so assuming a pair is in use, that's 10w. Not so great, but do-able.

    Put your hand on yours and tell me thats just 5 watts??

    You know, your selfishness really surprises me.

    I wish you lived near me, it would be good to make you the 1st legal test case.

    As you are, it would seem infringing the conditions of your TV licence and knowingly causing harmful interference with no concern for the victim.

    What if there is a elderly person near you who's only fun in life is listening to the amazing world of shortwave radio?

    And now because of your attitude and inability or lack of interest to find an alternative they have lost everything?

    Don't doubt it! probably a large number of shortwave radio listeners fall into this category.

    They won't be well connected via the web etc, they will just be carrying out their harmless interest and now, because of BT and Comtrend and the other shameful PLT makers and distributors their life has been spoiled!

    But I guess you are a product of the modern world and don't give a stuff for anyone.

    Long as you are ok eh!!!!!!!!!!!!

  76. Anonymous Coward
    Thumb Down


    Installation + BT != engineer.

  77. Anonymous Coward

    @ UKQRM

    Ever put your hand on an 11 watt energy saving bulb after it's been turned on for an hour or more? That's hot too. Indeed, I can't keep my hand on one for more than a few seconds due to the temperature it has reached. My adaptors get slightly warm to the touch, but I wouldn't imagine more than 35c surface temperature. I'm perfectly happy to believe that their energy consumption is 5 watts. That said I haven't seen any examples of somebody having connected their adaptor to an energy consumption monitor like the Kill-A-Watt.

    I have no TV license. I have a plasma screen with no tuner attached, it is merely connected to the home theatre PC and DVD/Blu-ray Player. I'm starting to get a bit bored of the constant letters from the TV license chasers, who seem adamant that I can't live my life without any form of TV tuner; well, I'm perfectly fine without one. No, I don't have BT Vision, I purchased the adaptors from Ebay.

    I wonder what alternative I do have; as I have plainly stated, I cannot run CAT5 through my apartment. I'm forbidden from performing any structural work, so cannot place the cables in the walls, ceiling or floor cavity. I have to get permission to even put a nail in the wall to hang a painting up, so I find it unlikely that the landlord will approve of the idea of running cables between each room (currently have 3 PLA in place, in different rooms). WiFi doesn't offer anything like the bandwidth requiredm not by a long shot. Can anyone name another option to connect these machines with sufficient bandwidth?

    That said, what if there *isn't* a short wave user residing within range? Why should I have to stop just on the presumption that there's somebody there. As you plainly and correctly state on the UKQRM site, if there is interference to short wave radio communications, an affected user is more than welcome to contact OFCOM, who will act as required. Until such time as I am contacted by them to inform me that my actions are having an effect, I will continue. I'm more than happy to stop if I learn that my actions are _certainly_ affecting someone. I'm happy to give a stuff, when I know it'll help for one to be given.

  78. Paul Banacks


    I suspect you're just trolling. However:

    "That said, what if there *isn't* a short wave user residing within range? Why should I have to stop just on the presumption that there's somebody there."

    Given that you *know* that these devices almost certainly emit harmful interference, that's disgustingly selfish. You are not able to make such a presumption now and certainly not in the future.

    You state that an affected user can contact OFCOM for help. Did it occur to you that an affected user may simply think their radio doesn't work any more? That they are unable to attribute it to your deliberate interference? Not everyone reads TheRegister. Your deliberate interference will cost those users countless hours trying to rectify a situation that they ultimately can't fix for themselves. They may not know that OFCOM can/will help and they may very well just give up. And that's all thanks to you.

    Long as you're ok, eh?

    p.s. I stopped using my PLT's immediately upon discovery of this issue. I have not yet implemented an alternative.

  79. UKQRM

    By Anonymous Coward Posted Tuesday 20th

    Yes maybe he is just trolling but he has said he would remove them if he finds out "actions are _certainly_ affecting someone" well, I can state categorically that yes they are!

    There must be a SWL within 500 yards of him.

    A 11 light bulb gets hot because of the fact its making light.

    Anyway heat is not the question here.

    Just because its easy or convenient does not make it right.

    It would be easy for me to speed when I go and visit my mum who is quite unwell! it would give me a nice bit of extra time there.

    And most probably I would not get caught by the police.

    So should I do it? should I say to myself, oh screw anyone that I might kill, this is going to be good for me???? is that the world you wish to inhabit?

    You could easily run cables to carry your data around your flat without 'installing' them in any way.

    If you wanted to you could do it. Just run them loose with a little tape to hold them in place.

    If you wanted to you would find a way around it.

    What would you have done if there was no PLT?

    Anyway the trolling alert is well made and I am very encouraged to see that Paul Banacks says once he learnt of the issue he stopped using them! thats an example of a fine person that does not think just of themselves! getting more rare these days sadly!

    Cheers for now


  80. Anonymous Coward
    Anonymous Coward

    Well again if it was me:

    How do you categorically state that there certainly must be a listener within 500 yards?

    If a SW user or listener had a problem, surely they would consult friends or relatives? We are all discussing this matter via the internet; if your internet connection was knocked out, surely you would contact friends via other means to establish the problem - I know I would. The videos posted on this article demonstrate how easy it is to locate the interference using nothing more than a battery powered portable SW radio and a small walk to triangulate and hone in on the problem. A knock on the door and a civil discussion would indeed result in the immediate cessation of the PLA's use.

    As for the heat, in the vast majority of cases, inefficiencies in any device cause it to produce heat. A tungsten filament light bulb might transform 60 watts of power into (say) 5 watts of useful energy from EM radiation in the visible spectra, the remaining 55 watts would transform into heat. Similarly, a television might use 200 watts, of which 100 watts is converted straight into heat due to inefficiencies. These PLAs might well consume 5 watts, of which 4 becomes heat and 1 is used to actually perform the task at hand.

    If I had been aware of this prior to purchase, I would have spent that part of my budget on another technology, more than likely 802.11a wifi, which operates in the (currently) less crowded 5Ghz band, rather than the packed 2.4Ghz band. Sadly, as a student I don't have the money available to chop and change what I own on a whim. Please rest assured, if CAT-5e networking had been an option here, it would have been employed rather than spend the money on powerline. Far cheaper, and greater bandwidth than PLA could offer. Plus, I would hardly draw a similarity between a radio user being irritated, and someone being hurt or injured in a car crash.

    Still, there we are, that's how it is for this reg reader. I await a knock on the door, there's a friendly chat and a cup of tea waiting, and if I have caused any QRM interference directly, a sincere apology.

  81. UKQRM
    Thumb Up

    In reply

    Well, I guess that's more fair than I expected!

    If you want to make sure you could look around and see if anyone has any wire antennas etc nearby you.

    That would be the proactive thing to do.

    Knocking on doors is something that terrifies a lot of people.

    They just don't know who is going to answer, ok so you will be nice but there is no guarantee.

    Its ok for a big ugly like me but imagine a frail person!

    Anyway, I am glad to see you would have taken another route if you had known about this!

    For that I thank you and hope that you may yet choose this other route later.



  82. Anonymous Coward

    @AC: still looks rather selfish to me

    naah, still looks completely selfish to me.

    He's basically saying, "I know these devices interfere with other peoples enjoyment but it's not my problem. Someone else should spend their time (and money) tracking me down."

    All the other things like not laying cables (really, how hard can it be) just sound like excuses. In other words, "I've got my solution it works for me myself and I so why should I change it." Instead, he should go without unless he finds another solution.

    Finally, it is my opinion that he has admitted to a criminal offence which upon conviction could land him a year or two in jail. The Wireless Telegraphy Act 2006, s68 creates an offence for a person who "uses apparatus for the purpose of interfering with wireless telegraphy." He knows or strongly suspects these devices interfere with wireless telegraphy and yet he continues using them, so it would not be unreasonable to suggest that he is purposely and deliberately interfering with wireless telegraphy. The fact it's a side effect of making a network connection using supposedly CE certified equipment is neither here nor there.

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