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Ofcom moves to protect Freeview interference from 4G mobile devices

Don't worry - Ofcom will ensure that everyone effected by 4G interference will still be able to watch digital television, and at no cost to the affected viewers.

Don't worry - Ofcom will ensure that everyone effected by 4G in
published on UK Free TV

Ofcom has estimated it will cost £100m to deal with Freeview users who are located near to the transmitters for the next generation of mobile broadband services, which will use the frequencies (791 to 862 MHz) previously used for analogue television.

Once switchover is complete, over 10 million homes in the UK will use Freeview for their only television reception, and almost all of the remaining 17 million homes will use the terrestrial digital television service on their secondary TV sets.

The signals are provided from two types of transmitter. First there are around 80 high power transmitters located on hills that serve very large areas, such as the Crystal Palace transmitter (4.5 million homes in London), Winter Hill (2.7 million homes in the North West of England) and Sutton Coldfield (1.8 million homes in Birmingham). In addition there will be over 1,000 fill-in Freeview light transmitters, such as Boddam, which serves just 600 homes.

In contrast, the new 4G mobile services will use around 9,000 smaller transmitters located near where the services are required, which follows the current model for mobile phone networks.

4G transmitter interference location

In places where the 4G transmitter is located close to homes receiving Freeview, it is likely that Freeview viewers will experience to forms of interference:

Signal overload - when a Freeview receiver is overloaded because the total input signal level is more than a certain level, the whole receiver will stop working and all television services will be lost.

Signal-Interference Noise Ratio degradation: this is where reception breaks down because the receiver can no longer decode the digital information in the transmission. This could affect a single multiplex or could take out all services.

The "overload zone" will occur for Freeview viewers located close to the 4G transmitter, with the "degradation zone" will affect those slightly further from the 4G transmitter:

Interference factors

Not all 4G transmitters will cause problems for Freeview reception, the other factors are:

The types of Freeview installation, with single unamplified aerials to a single set have the best resilience, with communal and systems with amplifiers more likely to suffer. The 4G transmissions are capable of overloading most types of TV amplifier.

The frequencies used for the DTT services being received, with those on the adjacent C60 being worst, C52 to C59 second worst and those on lower frequencies having the best chance of avoiding interference.

The strength of the Freeview signal received is another factor, with those with weaker signals due to being distant from the Freeview transmitter, having the most potential for 4G interference.

Not all 4G transmitters will use the same frequency, those that happen to use the lower frequency allocation having the most potential to cause Freeview interference, and those that transmit at higher power levels having more effect than low power 4G transmitters.

Homes affected by 4G interference without intervention

Ofcom calculate that:

Of the 16.3 million UK homes with a standard (unamplified, unshared) Freeview reception, 110,000 (0.67%) would be effected.

Of the 5.2 million homes using communal aerials systems, 550,000 (10.6%) will have problems.

Of the 5.6 million homes using amplified Freeview reception, 100,000 (1.8%) will experience problems.

Prevention and mitigation

There are several ways to deal with these 760,000 homes that will have problems.

Signal filters

Use of signal filters for the Freeview reception combined with Fitting of filters at 4G transmitters.

Ofcom's modelling finds that this is the most effective way of dealing with the 4G interference problems. Of the 110,000 standard Freeview installation homes, 87,000 will have their reception restored this way, almost 100% of the 550,000 homes with communal systems will be mitigated with filtering and 93% of the 100,000 domestic installations with amplifiers.

The total cost will be £20m for the Freeview filters and £33m for fitting of the filters in homes. Also, for the domestic filtering to be effective, the 4G providers will also have to spend around £11 fitting filters at the 4G transmitters when they are being installed.

Freeview equipment adjustment

After the provision of filters, there will still be 23,000 homes with unamplified and 7,000 homes with amplified Freeview reception equipment that are unable to receive their services.

Some of these homes will simply need a new Freeview box for each TV set. Whilst these boxes cost around £15, the requirement to fit these and provide for each set could come to as much as £200.

Another option, for at least 20% of homes, is to receive the Freeview services from an alternative transmitter. However, this could lead to the provision of the 'wrong' version of BBC One, BBC Two, ITV1 and Channel 4/S4C to the home. Ofcom is unsure if this will be an effective mitigation.

On Channel Repeaters

The use of On Channel Repeters (OCR) to rebroadcast the Freeview signals at higher power levels in the interference area was considered by Ofcom, but the high cost and unknown effectiveness has caused them to be distrgarded as a viable option.

Ensure 4G polarization is opposite to Freeview polarization

Because of several factors, Ofcom does not consider that this will help prevent 4G interference of Freeview reception.

4G transmitter power reduction

Ofcom have concluded that causing service reception problems for the new 4G mobile services is undesirable for the services to be successful.

Provision of Freesat or free Virgin Media services for affected homes

This leaves providing a replacement Freesat installation (including multiple sets and Freesat+ boxes) for the 30,000 homes with their Freeview reception disabled, or the funding of a basic Virgin Media package. The total cost for this is £10m.

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Tuesday, 13 November 2012
6:13 PM

We had a perfect signal until 31st Oct. Now we can't get a picture at all on all channels except BBC1/2 and audio is very severely disjointed on all other channels so you can barely make out a whole word here and there. Help!

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vicki's 1 post GB flag
vicki's: mapV's Freeview map terrainV's terrain plot wavesV's frequency data V's Freeview Detailed Coverage
Wednesday, 14 November 2012
Mike Dimmick

2:24 PM

vicki: Well, there haven't been any changes at the transmitter and Digital UK's prediction suggests that you need barely any gain from the aerial, so my guess is that either a cable has become disconnected somewhere, or that the aerial has been damaged or moved, or possibly that water is getting in somewhere.

All outside cables should be well anchored down to stop them moving, and rubbing against tiles or brickwork. If they do rub, the insulation wears through, which allows water to get in. Water changes the way the cables work, massively increasing the signal loss in the cable.

You are very close to the transmitters, so it could be a case of receiving too much signal, though I can't see why the received signal level would have changed. If you have any amplification (boosters), try removing it or turning it down. If that doesn't help, and nothing apepars to be broken, try adding an attenuator.

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Mike Dimmick's 2,486 posts GB flag
Mike Dimmick

2:29 PM

vicki: Additional thought - there was a retune event on the 31st, reorganizing the channel list. Did you retune? If so, it's possible that your equipment has stored a different transmitter from the best one available. Try doing a manual retune using Mendip's frequencies (if you had Freeview before switchover), which are: C61, C54, C48, C56 and C52 (and also C58 if you have HD).

You might find a better version of the services at a different place in the channel list, usually around 800 or so. If so, check which UHF channel/frequency those services are using, and retune manually using those frequencies.

Signal levels do vary over time, with changes in the weather conditions. It's possible that when you retuned, conditions were *just* good enough to detect the other transmitter and store the services. TV equipment should really check the quality and strength of each transmitter before deciding which version to store, and newer equipment (most Freeview HD boxes) does. Older equipment just stores the first version found when scanning from lowest to highest frequencies.

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Mike Dimmick's 2,486 posts GB flag
11:55 PM

My Freeview reception is from Winter Hill and so I was concerned to read the news today (see below) that Winter Hill is likely to be one of the worst hit areas for interference from 4G. Any ideas why? Also, what exactly do the filters do (see below) - will they block reception to a mobile phone as well? Also, what is a 'professional refit'.

"The government has promised filters to homes in the affected areas that will block the 4G signal or £50 towards a professional refit, which will be paid for from the £180 million pool provided by mobile companies.

The areas likely to be worst hit identified by OfCom include those served by the Crystal Palace transmitter in London and the Winter Hill transmitter in Lancashire".

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Paul's 12 posts GB flag
Thursday, 15 November 2012
Dave Lindsay

10:49 AM

Paul: At a guess I'd say that the reason is that Winter Hill is second behind Crystal Palace for the number of viewers served!

This would appear to be a story born from statistics.

The filter fits inline with the aerial lead to prevent the 4G signal (which is being picked up by the TV aerial) from reaching the TV receiver.

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Dave Lindsay's 5,724 posts GB flag

8:41 PM

What insertion loss in dB can be expected?

For some with fringe reception, this might mean
falling of the "cliff edge".

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michael's 869 posts GB flag

9:56 PM

I'd have thought Crystal Palace would be fine given it's well below the 800MHz band that is being auctioned off for 4G - that is UHF 61 and above - Crystal Palace uses UHF channels in the 20s.

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Michael's 358 posts GB flag

10:26 PM

Michael: I would guess that Crystal Palace comes to be mentioned due to the large number of viewers served who will be using communal aerials. Problems could arise when a weak Freeview signal is accompanied by a strong 4G signal. If this combination is amplified with a wide band distribution network there is the possibility that the resulting very strong 4G signal could overload the tuners in viewers' receivers. As you say the CP uses frequencies below C37 which makes filtering easier. Some viewers will need to use group "A" aerials to concentrate the gain on the required frequencies and good quality double screened coax to minimise unnecessary pick up of the 4G signals.

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KMJ,Derby's 1,811 posts GB flag
Monday, 19 November 2012
rosemary porter
7:59 PM

I have just been told about the G4 aerial.
I live opposite the Crystal Palace mast. Please tell me how I will be affected and when

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rosemary porter's 1 post GB flag
Friday, 7 December 2012
12:55 AM

I live in Pinner, Middlesex, receiving a strong signal from Crystal Palace, group A channels. The start of the 4G transmission from EE resulted in loosing ch 22 and 28. My aerial is a wide band type so I bought and fitted a band pass filter, for group A channels, and fitted it between the aerial and amplifier. The signal strength and signal quality are now both at their maximum and all channels are restored, including the HD ones. The filter cost £9.54 plus delivery and took about ten minutes to fit. The insertion loss is 2db.

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Michael's 1 post GB flag
Michael's: mapM's Freeview map terrainM's terrain plot wavesM's frequency data M's Freeview Detailed Coverage
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