back to article BBC engineers see PLT knocking out DAB

Recent experiments carried out by the BBC demonstrate how power-line networking can interfere with FM radio and knock out DAB entirely, but only for those who get a decent data rate. The new study was commissioned by the BBC and authored by one current and one former BBC engineer. The study examines transmissions coming off PLT …

COMMENTS

This topic is closed for new posts.

Page:

Silver badge
Troll

Hmmm, I wonder which is more useful?

PLT or DAB?

5
4

I wonder which is more useful?

Ofcom or BBC?

0
1
Paris Hilton

Various evils

Neither technology is fantastic really, but quite frankly I would rather do away with DAB. A 20 year old technology with limited take up, poor performance and no strategy for upgrade? Fab. At least Powerline Networking has a roadmap!

DAB has sold about a million units, I think, of those no one knows how many people are actually using the DAB part. The technology is ancient and uses old error correction techniques, simple modulation and a simple codec. Yet, because it is quite unique and hasn't a large take-up (worldwide) it still costs a fortune to buy the components. Overall it would be cheaper for everyone to abandon it, just transmit some public service channels for a few more years (5?) and move to a better system before the forecast sale of +50million UK digital radios really kicks off.

Replace it with DVB-T2 which can have profiles for very robust mobile reception, could achieve national coverage quickly and the components would be at commodity pricing instantly because half a dozen other countries are using (or planning on using) it for their TV delivery. It would also be compatible with UK Freeview HD products and thus wouldn't involve duplication of equipment for those that had a Freeview HD product.

Although I do appreciate that channels might be duplicated because they are already broadcast on DTT but not in a mode which is mobile and so broadcasting them on DTT would allow them to be broadcast in HE-AAC for good quality, with highly resilient error correction for in-door reception and a decent timing mode to allow for reliable mobile reception.

Yes, sorry those who already have a DAB radio, but for most people DAB sucks.

Paris, because she's always up for something new.

3
0
Bronze badge
Thumb Down

Figures

You might wish to check your figures. Leaving technical issues aside, in 2010 alone about 2M units were sold in the UK (source http://www.zdnet.co.uk/blogs/jacks-blog-10017212/dab-radios-declining-sales-eforum-revisited-10022187/)

0
1
Anonymous Coward

One man and his hobby.

Would that be Simon Quinlank? Mine's a flask of weak lemon drink.

5
0
Thumb Up

Weak lemon drink

Drink it! Drink it now!

2
0
Thumb Up

You're not a hobby horse...

...you're a hobby Lion!

I dunno, sounds like the Beeb want the Moon on a stick.

Mine's the one with Alan Milk Carton Body in the pocket :-)

Rob

0
1

FM vs DAB

"FM radio can scale back from stereo to mono when necessary, and can cope with quite a bit of interference before becoming unintelligible"

This, my friends, is why I won't be switching to DAB any time soon.

18
0
Anonymous Coward

Re: Fm vs DAB

"DAB is particularly vulnerable to interference as it either works or it doesn't, with just a small change in signal strength flipping it between the two. FM radio can scale back from stereo to mono when necessary, and can cope with quite a bit of interference before becoming unintelligible – though listeners may decide to tune out before that happens."

I was under the impression that, although the jump from "working well" to "not working at all" for DAB was swift, it happened at a comparable signal level to when FM would drop from "fuzzy mono" to "bugger all".

In other words, for a comparable weak signal strength, when FM was only managing mono output, DAB would still be giving you clear stereo.

Personally, I've never understood all the DAB hate that exists - maybe cheap DAB radios are worse than cheap FM radios...

7
7
Bronze badge

DAB hate

The problem is the bit rate. It has been wound down too far in order to squeeze in more channels at the expense of audio quality. In some circumstances it will give a clear signal where FM fails, but the clear signal suffers from compression artifacts which are not present on FM (and to a much lesser extent on radio channels on DTT [Freeview] because the bit rate is higher and the compression more sophisticated). So the best DAB is much worse than the best FM.

5
0
MrT
Bronze badge

There are no cheap DAB radios...

...or at least none in the same price bracket as a cheap FM radio - eBay has FM sets for £1.25, including headphones, but DAB seems to kick off at about £15 (seen at Tesco), and in both cases decent kit is a *lot* more than that. Some of the hate might be because of the cost...

Mind you, I like DAB for what it gives - I've a Pure One Elite in the kitchen and my car has DAB built-in, and apart from being noticeably, but not by much, quieter compared to FM, listening to DAB is just fine.

3
0

the quality of the message matters too

apart from radio 3 there's essentially nothing on any uk radio that justifies or needs a high bit rate. if the content is shite it makes no difference what the bit rate is: it's just not worth listening to.

4
4
Anonymous Coward

"The problem is the bit rate."

I agree. 64kbps on some channels. Welcome to 1995.

2
0
Silver badge

Ofcom is still digesting the research and will let us know when it has....

found enough cash down the back of the sofa to pay back the _massive_ bung they clearly got to look the other way when PLT sneaked in.

14
2
Thumb Down

F*** Amateur Radio

This makes me sad. I was into amateur radio as a child, it was great to learn basic electronics on.

Power line telecommunications - that's just broadcasting on unshielded antennas.

What we need is a magnitude 6 earthquake in the middle of London - lose all our mobile phone towers and cabled communications - then see how little respect everyone continues to have for amateur radio enthusiasts.

19
5
Gold badge
Grenade

Re: F*** Amateur Radio.

So, zero respect and an irrelevance for the next few millenia at least then?

1
9
Thumb Down

Re: F*** Amateur Radio

Ask people in places affected by storms, earthquakes tsunamis, terrorism if amateur radio is 'an irrelevance for the next few millenia".

After the Twin Towers attacks, Japanese earthquakes, Haiti, etc amateur radio was the ONLY form of communication - which is why the pollce & military turned to them.

Of course, the UK is immune from Lockerbie-type disasters (yes, radio hams were out with the search parties).

Yup, zero respect, but only from those with their head so far up their a**e they don't realise they can't use their mobile when the battery is flat or the repeater is damaged.

18
2
Dead Vulture

ilk

"only interfered with the kit of radio hams and the like"

2
5
Anonymous Coward

ilk...

..."a group of entities that have common characteristics such that they may be grouped together."

Wiki

2
0
Silver badge
Headmaster

ilk...

You may be disappointed to learn that Wikipedia is not entirely reliable.

"ilk" means "the same", hence "Sir Angus MacSporran of that ilk" means that he is the MacSporran of (the clan) MacSporran.

0
0

But, but, but...

Ofcom have already thoroughly tested the devices and found "THERE ARE NO PROBLEMS, NOTHING TO SEE HERE". Surely they weren't lying?

12
0
Anonymous Coward

Hmmmm show of hands.

At home, in 2011, who would prefer a radio signal over having the internet/a network connection?

0
17

you can have both

If you use WiFi or Ethernet.

Though I suppose PLT is okay if you get agreement from every house within 500 meters of yours, that they don't mind having their DAB jammed so you can use your internet. I can't really see anyone agreeing to that, even if they do hate DAB.

15
3
Thumb Down

But you can have both anyway

I used to use PLT and never noticed any DAB (or FM) reception problems at home (since rearranging things and running cabling to get gigabit ethernet connection I no longer use the PLT kit). I'm guessing it depends on the exact PLT kit used, the state of the wiring and the positioning of the radio, so I don't think there's any need to be alarmist about this.

4
7

The title is required, and must contain letters and/or digits.

I use PLT in my house. I also have no problem listening to my DAB radios. Seems like a non-issue to be honest

3
11
MrT
Bronze badge

Same here...

Is this more likely to be a problem affecting network transmissions over HT powerlines, such as the ISP to home link being carried along high-level pylons?

0
2
Flame

@Richard 22, @Oddlegs

How many more times to we have to say it, the current batch of PLT only affects HF radio. This report is based on the new Gigle chipset units from Belkin and Solwise. They use frequencies up to 320MHz which affect the VHF band.

It is not alarmist - it's education!

8
1
Silver badge

"only"

Sadly, long range radio listening on HF has become pointless just as a new generation of software controlled radios was making the hobby innovative again.

I really miss listening to Strauss from Vienna on 12MHz, and one of the high points of my life was listening to the Bernstein "Ode to Freedom" performance on Deutsche Welle's short wave live coverage.

http://www.amazon.co.uk/Beethoven-Symphony-Freedom-Bernstein-Berlin/dp/B000001GDR

3
0
Anonymous Coward

Very particular selection of product used for tests...

Interestingly, the report seems to go out of its way not to mention which PLT kit it is - except to say that they have chosen ones that go up to 305MHz.

Anyone who knows anything about powerline home networking technology can tell you it's a pair of Belkin "Gigabit" adapters, using the Gigle chipset (you can recognise the product in the pictures if you know what you are looking for).

So - they have selected the least deployed chipset of all, one that is renowned among engineers for its poor noise immunity performance (you will find online reviews give poor ratings for bandwidth, it's not only those with technology knowledge), and the only one available to use frequencies above 68MHz (almost all are under 30MHz) and make disturbance to DAB signals. The reviews of these Belkin products were bad enough to make the product quite difficult to find for sale nowadays.

The claims of radio amateurs that PLT equipment will disturb over 500 metres away are false for any products on the market today (even if ever they could be verified) - whilst I would agree that the old Comtrend products using old DS2 "UPA" chipsets were bad products in their ability to disturb and in performance terms, products applying the HomePlug AV specification without any proprietary extensions (as in the Belkin 1Gbps) do not have issues (unless you are a radio amateur who will tune out of amateur bands to find low level emissions very locally to your special antenna).

1
6
Silver badge
FAIL

on a similar note...

my car runs like stink on plutonium...

your kids health??? not my problem mate

4
3
Silver badge
Coat

@AC 10:06

So what are you saying? Someone is having a Gigle?

0
0

Sheer Poetry

Something the majority don't want (DAB) knocked out by something Ofcom refused to deal with. The powers that be get their comeuppance in the end :-)

12
0

Want

Do people actually not want DAB or is it just that people in areas with poor reception don't think it's any use?

For me it's a tremendous improvement over AM/FM - probably 80% of my media consumption is DAB radio (although the admongers would be less keen to know that 99% of that is advert-free BBC).

If I couldn't have it, I'd certainly miss it; frankly I'd probably even pay for it.

4
3
Silver badge

Hate

DAB is a geriatric solution to a problem that does not exist.

Originally conceived as a way of automating radio listening so that people did not have to re-tune their car radios as they drove along, or suffer fading from multipath it was also adapted to increase the number of channels available by TDM. But we are not short of FM spectrum, particularly when so many local commercial radio stations have been merged into national conglomerates. And a serious attempt to measure the artistic quality would be very disappointing. Very dissapointing indeed.

The battery consumption of portables is appalling, and the level of technology required means that cheap radio is impossible. And the abysmal bit rates drive the final nail into the coffin from my point of view.

Oh, and as early adopters, nay originators, we are lumbered with a system that the rest of the world has moved on from.

We have internet capacity enough and satellite channels that cover all the stations (although the satellite channels are under-utilised, being fed from the low bit rate DAB channel in too many cases). Our american cousins, for all their failings, have adopted satellite receivers for cars rather than DAB, and we could do the same. On the subject of internet capacity, that could be improved if ISPs put simple caching servers in the exchanges, so that multiple consumers of radio or tv could be given a single feed over the backbone, rather than multiple identical feeds occupying bandwidth.

And yes, I live in an area which is "marginal" for DAB, but then it is "marginal" for FM, DVT, rdio 5 MW, and broadband as well. If DAB were any good I'd be putting up antennae

2
0
Megaphone

Re: DAB solves nothing

I agree - what is the point of DAB? FM serves a purpose - a constant amplitude signal that can easily be tuned into by a phase-locked-loop.

AM also serves a purpose - dirt cheap receivers.

Why add DAB to the mix? For one it limits sound quality - secondly it requires complex kit - thirdly it prevents any hobbyists (e.g. children) from ever building their own receiver kit - 4th it makes a LOT of cars/receivers mere industrial waste (radios have to be some of the longest-surviving hardware that continues to be in use, unlike computers which get trashed every 3 years).

I'm against DAB. Digital video - yes, that makes sense, more channels, great. But FM - I like my car radios, the simplicity of the technology (and it was a fantastically simple but elegant solution for high quality radio reception in challenging conditions - even lightning struggles to disrupt a FM signal).

3
0
Anonymous Coward

hmm

does PLT bugger up digital tv reception as well? I get quite remarkably bad and suspiciously erratic digital tv reception in my new place.

1
1

It is possible.

PLT launches a considerable amount of RF energy on to the mains wiring. When this energy hits non-linear devices, such as the bridge rectifiers found in Switched Mode Power supplies, it created intermodulation. This can result in spurious harmonic energy reaching frequencies as high as 1GHz (this had been observed and was listed in the recently extracted Ofcom EN55022 test documentation). This harmonic energy is carried via the mains wiring in to devices such as your television, and if they lack suitable filtering components, or those components are failing, the harmonic energy can leak into the electronics and cause problems. It is not a precise science either - the application of a finger, or a test probe, can alter the dynamics and make the problem worse, or disappear altogether.

7
0
Boffin

Factual?

"Power-line telecommunication (PLT) involves sending radio signals over mains electrical wiring."

Erm. Radio signals over mains electrical wiring. I think someone needs to revist tech 101. It might be an analogue wave form, but that does not make it a radio signal. Now, one it "broadcasts" from the wire ... thats a different matter ;)

3
6
Anonymous Coward

It's still a radio signal when it's on waveguides

These things *are* radios, they're just trying to use your average (completely unsuitable) twin-and-earth wiring as a waveguide, supposedly to avoid broadcasting the radio.

The tests we did a while back showed that ring mains made from twin-and-earth always turned into pretty good antenna to broadcast, generally pretty detuned so very wideband.

Radial circuits were ok if you put suitable filtering at each end and properly terminated them, as otherwise everyone on your phase of the supply could listen in - the meter doesn't actually block it, though the substation transformer did.

So they may well be suited to mainland Europe and the US where ring mains are rare - if you can pursuade everyone to fit a termination block to the end of all their radial wiring and a massive filter at the incomer.

7
0

title etc

I think it's perfectly reasonable to call these radio singnals in the sense that there is not a cat in hells chance that anything in the frequency ranges that PLT uses is going to stay confined to the cable.

This whole "but it goes down the wire so it isn't radio" is exactly the area of ignorance that the manufactures are seeking to exploit. I'm not saying your wrong, but people who are concerned about the spread of this tech really need to hammer home the fact that these are essentially radio devices, they just happen to share a antenna between them.

10
0
Anonymous Coward

Finally, a sensible article from Bill Ray

Thank you Bill for finally writing an article which mentions amateur radio and doesn't take the piss.

Perhaps now these reports from Ofcom and the BBC have been published, the problem will be taken seriously because despite what Ofcom had hoped, it won't just go away.

9
1
Megaphone

Not fit for purpose

Although a first reading of the EMC directives yields the rather circular statement,

"The apparatus shall be so constructed that

equipment shall not generate electromagnetic disturbances exceeding a level allowing radio and telecommunications equipment and other apparatus to operate as intended;

equipment shall have an adequate level of intrinsic immunity from electromagnetic disturbances to enable it to operate as intended."

further research shows that there are actually relevant standards (with well defined, quantified limits) to which equipment must adhere. Moreover, OFCOM's own research has show that PLT kit fails to meet these requirements:

http://www.theregister.co.uk/2011/03/31/ofcom_plt/

I would suggest that Trading Standards might be more useful, as products have to be EMC compliant to be CE marked, and it is their job to police this.

I've recently been trying to deal with RF interference in the LW and MW bands knocking out my ADSL connection. OFCOM proved similarly useless and uninterested in this situation, spending a week telling my ISP that I had to pursue this with then (i.e. OFCOM), and telling me that my ISP had to pursue it with them. Eventually, they confessed to my ISP that they were no longer interested in policing interference at these frequencies, and that it was essentially a free-for-all.

4
0
Boffin

Interference with BT Infinity?

Further research yielded some test results[1] which show that PLT devices transmit on 2MHz upwards. ADSL2 uses 25kHz - 2MHz, and thus should be unaffected by PLT, but VDSL (as used by BT Infinity) uses up to 30MHz, and looks somewhat vulnerable to interference. If anyone's in a position to test this, I should be very interested to hear their results!

[1] http://www.ban-plt.co.uk/tests.php

3
0
MJI
Silver badge

BT do both

Installed Infinty and sent me new Powerline adaptors.

Why do I need them when I have a perfectly good piece of Ethernet cable to the BT Vision box.

2
0
Anonymous Coward

VDSL and PLT

VDSL and PLT are commonly used together in Belgium (highest deployment of VDSL in Europe) to deliver TV over IP (more than 40% of IPTV subscribers use them).

Belgacom (the Belgian incumbent telco) are certainly in a position to test this, they supply both the VDSL and the PLT adapters....

0
2

yeah

but they don't have ring mains in Belgum

3
0
Anonymous Coward

Description

"Power-line telecommunication (PLT) involves sending radio signals over mains electrical wiring"

Can you add a word to that description please? It doesn't send radio signals down the wires as such it sends signals down the wires at the same frequency as radio transmissions. So can you stick the word frequency between "radio" and "signals"?

2
8
Unhappy

Why is it...

after sitting exams, paying for licenses, calibrating my equipment to 5 decimal places of a MHz and reporting every contact I make via my legally required log book... if I cause the slightest bit of rf interference ofcom can come in and confiscate my entire multi thousand pound set up.

And yet when my local "I know everything about networking", PC world loving neighbour wipes out everything within a 50 MHz range with broadband radio interference it's called progress?

And by the way, there is a hell of a lot more radio traffic below 50MHz than just amateur radio. http://www.fcc.gov/oet/spectrum/table/fcctable.pdf

21
0
Anonymous Coward

so

get yourself some plt gear and if they come knocking, blame it on that.

5
0

You don't need a logbook

Although I agree with the substance of your comment, you are mistaken if you think that a logbook is "legally required". Ofcom can require you to keep a log, but unless they do so (generally because they are investigating reported interference) there is no legal obligation to do so. Paragraph 12(1) of the terms, conditions and limitations:

12(1) For the purposes of any interference investigation, to determine compliance with the terms, conditions and limitations of this Licence, or for any other matter concerning the enforcement of any relevant legislation, the Licensee shall at the request of a person authorised by Ofcom, keep a permanent record (a “log”) of such matters concerning the operation of the Radio Equipment, over such period, and in such form, as the authorised person may require.

1
1

Page:

This topic is closed for new posts.

Forums