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back to article UK.gov vows to purify TV with £180m from mobile networks

Bored of waiting for Ofcom's consultation on the possible interference between 4G telephony and Freeview TV, the Ministry of Fun has said it will spend £180m of operators' money mitigating the problem. Ofcom has been looking into the matter since July, and is expected to publish a report soon. But it shouldn't be a surprise to …

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Bronze badge

Problem is not due to signal boosters.

"The only people who are really going to have problems are those receiving television on channel 60 or above (see this helpful map from UK Free TV) who are also using powered signal boosters. These take in the signal and amplify it, but they also amplify the interfering signal and can make the two indistinguishable, so it's those users Ofcom (and the Ministry) will be targeting."

What a nonsensical way of describing the problem. Powered signal boosters do not make the two signals indistinguishable. What causes the problem is that the Freeview signal is very weak in the first place (hence the need to boost it) and that the addition of extra interference from an adjacent 4G channel will reduce the SNR below what is required to decode the Freeview channel. So it's nothing to do with the use of signal boosters as such - it's simply because such boosters are used where the Freeview signal is already marginal.

A better approach would be to use "grouped" antenna to provide for more signal selection. Unfortunately, the early Freeview roll-outs involve a lot of "out of group" channels and wide-band antenna proliferated. I don't know if this pattern is repeated on the "final" Freeview frequency allocations, but if so it will not help the situation as wide-band antenna will be more vulnerable to such interference.

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WTF?

Re: Problem is not due to signal boosters.

So, you say the problem is down to signal boosters used in weak signal areas for Freeview, however you fail to note that if the Freeview signals were not weak then no signal boosting would be required.

The only alternative would be to increase the number of TV transmitters to provide stronger signals everywhere, thus doing away with the whitespace that is so valuable to the digital dividend merchants.

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Silver badge

Re: Problem is not due to signal boosters.

1: the booster amp or tuner inputs get overdriven into clipping by the 4G signal, wrecking everything.

2: AGC kicks in at the tuner, dropping the Freeview signal below the noise floor (but keeping the 4G clean ;) Buggy AGC goes into overdrive dropping everything too far.

Neither are good, 2 is cheaper to fix since the filters can sit at the tuner end. 1: may need a climb to the aerial which won't be a £10 job.

After digital switchover my signal is still poor enough that I could leave the masthead amp installed and there's still plenty of amp headroom. There are a lot of people that needed a booster before switchover but dont now. They don't have any headroom after power went up, see no problems yet so they didn't remove the amps. 4G will hit them swamp their amps.

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Re: Re: Problem is not due to signal boosters.

Well that makes more sense that the article, although my experience of masthead amps is they have a great deal of tolerance. I've seen a masthead amp deal with a combination of very strong and very weak TV signals. Of course if the 4G transmitter is close enough, and strong enough what you suggest could happen. Fitting a filter is a bit of a pain with a masthead amp as if it's to sort out clipping or AGC as you suggest, it will have to be up the mast too. It would also have to have a very steep roll-off, which implies it might have to be active.

Perhaps it would be better to introduce masthead amps & boosters that cut off the frequency response at channel 60.

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I thought that the point of all this digital TV stuff was to free up channels that we couldn't use at the time because they would interfere. The concept was, correct me if I'm wrong, along the lines of:

"We'll move all the TV into its own frequency band that takes up less room - then that leaves us buckets of old very sought-after analogue space that we can use willy-nilly and not worry about taking out someone's TV signal".

I will never understand Ofcom and frequency allocation at all. Either allocate something or don't. If you do allocate it, your whole JOB is to make sure it doesn't interfere with others at all. That's it. That's all you have to worry about. And you can't even do that.

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Anonymous Coward

£10,000 per house if your tv reception gets affected? I hope I'm one of the lucky ones!

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Anonymous Coward

Suddenly...

... my Sky subscription might disappear if the Gov are going to come and install some Freesat gear at no cost to myself.

Now just need to figure out how to overpower my freeview signal locally to complete the con.

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Flame

Re: Suddenly...

Newsflash Commentard

Basic Freesat boxes start from £40 - thats barely more than a monthly sky subscription if you want anything decent.

Even the Freesat HD PVR's amount to ~ 1 years sky subscription.

Therefore its not money stopping you - its knowledge and/or lazyness.

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Rob
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Go

Re: Re: Suddenly...

Just lazyness, only because I have been putting off the re-cabling job for the sat and ariel feeds across the whole house.

Just to be pedantic, £40 is a bit steep when you have already read that I have a Sky subscription You should have told me to spend £20 on the Freesky card to go in my existing boxes ;-)

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Why don't we just plan to give up Freeview and put 4G in tellies? Surely if 4G speeds are knocking around the airwaves anyway, it's enough bandwidth to stream channels. You can then stop broadcasting Freeview and make way for 5G.

The sooner we get *everything* delivered via internet the better (mobile phones, freeview, FM).

And if you think my idea is too far fetched, you missed the bit where this current plan allows up to £10k PER HOME to upgrade to freesat.

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Not 10k for freesat.

The 10K is where DVB-T (Freeview) is fubarred by 4g and Freesat is unobtainable due to, for example, location or building aspect.

The 10K per home is to enable the affected homes to club together in order to, for example, install a relay (e.g. 100 affected home at £10k = £1 million)

For most people Freesat will be an option and you will likely get offered a low-end Freesat SD setup (about £150 including installation).

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FAIL

Hands up who's "reliant" on TV

"...only 7 per cent of German households were reliant on terrestrial digital TV, compared to 41 per cent in the UK..."

Does it provide air / food / water for them or something?

Would these people blink out of existence without television?

We're in the frikkin' twilight zone here, man!

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Thumb Down

Re: Hands up who's "reliant" on TV

I would imagine that most people would understand that "reliant on terrestrial digital TV" infers "as opposed to another means of obtaining a television service" and doesn't mean "Reliant on TV as a form of life support".

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WTF?

10K?

What sort of set-up would you have to have where it would cost you £10,000 or more to have freesat installed?

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Anonymous Coward

My understanding of the £10K amount was that would only be for the tiny proportion of houses where any of the normally viable alternatives (sky, freesat, virgin, etc) wouldn't be possible.

Regardless, the whole thing is a bloody shambles, and I'm going to be well pissed if my reception (from the Angus transmitter) is affected. It uses two frequencies above 786Mhz from what I can tell.

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Anonymous Coward

What's the source of the story, what's their agenda?

Saw this on the BBC yesterday.

Not convinced it makes a whole lot of sense. Who published the press release, and what is their agenda?

Sure, like the case with LightSquared and GPS, strong interfering signals some way from the wanted (weaker) frequency can get through the receiver's insufficient filtering and cause problems. (And contrary to previous poster, wideband booster-amps /can/ saturate or create other intermod distortions.) Even so, bearing in mind that Freeview receivers have worked in recent years in the presence of much stronger ANALOGUE transmissions (usually from the same transmitter mast) so aerial equally aligned and on almost adjacent frequencies... I'd've thought the receivers should have pretty good off-frequency rejection. I can believe that there will be a very small minority of houses with genuine reception problems (e.g. where the 4G mast is only 50 yards from the customer house and in line with the TV transmitter, so the customers aerial is pointing straight at it), but 760000 homes affected sounds an awful lot...

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Re:

Has nothing to do with the receivers selectivity (*), if the boosters are overdriven amplifying leaked 4G, everything gets distorted. Selectivity can't fill in for a corrupted signal.

The research documents were published early last year on ways to mitigate the effects of 4G and more or less just presented the problem and costs, it seemd pretty neutral. Today's reporting is about which option's been chosen.

(* substantially stronger 4G could trigger AGC and drop the Freeview below the receiver noise floor. Not particularly likely but possible. Actually, I'd say it's extremely likely on cheap USB tuners!)

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Ch 60+?

By the time LTE gets going there won't be any TV signals on channels above 60. The interference will be worst in Ch 60, decreasing for 2 or 3 channels below that, and then not really a problem below that. Unfortunately OFCOM decided on skirt filter specs for LTE transmissions that mean there is still significant signal power at the top edge of Ch 60. Assume I'm beaming to my local TV transmitter on Ch 60 but there is a LTE basestation more or less on the same bearing. Even if I could put a brick-wall low-pass filter in front of my masthead preamp, I will still get significant LTE signals overlaying the DTT one. If I don't use a filter, the much stronger LTE signals just above Ch 60 will get into the preamp, perhaps overloading it, and into the receiver front-end, perhaps overloading that too.

£10k per house sounds a lot for amelioration. A Freesat installation will be much less than that. It won't work for everyone though.

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Silver badge

Re: Ch 60+?

FYI I'm receiving Freeview on C29,54,56,57,58&61 post switchover. Still praying they'll change their minds and have another reshuffle or I'm up shit creek in a couple of years.

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WTF?

Not impressed

Given that the channel 60 map shows I may live in an affected area, and it's taken me years to get my flakey freeview just right (pre and post switchover), and extended multiroom, I'm going to be pretty pissed if I get hit by this.

Especially as I already have Freesat. I'm a maximum free-loader and use Freeview and Freesat together given there are a handful of channels on one and not the other.

So this would have no upside for me whatsoever. Or 100% detrimental affect?

"Sorry we've broke your Freeview sir, but you already have Freesat as well so in your case we'll do nothing". Errrr... and what are they going to do to give me back reception of the channels on Freeview that do not exist on Freesat???

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Bronze badge

A more complete explanation

There is a rather better explanation of the issues here, which are by no means limited to using channel 60 with signal boosters. It appears that if you have a signal booster near a 4G transmitter it could kill the entire Freeview service or, if you are really unlucky, even without a booster. That's due to overload of signal levels into either the booster or the receiver.

The adjacent channel 60 interference issue also applies, but it's far from the only issue.

http://www.ukfree.tv/fullstory.php?storyid=1107051834

One thing that does occur to me as that this is based on modelling the 9,000 or so 4G base station. However, what about the mobile devices themselves? No doubt they are much lower powered than the base station, but many will be a heck of a lot closer to the TV aerials, and the inverse square law applies.

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