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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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Sunday, 26 February 2012

4:35 PM

David: The UK has already planned for this change for many years, but some transmitters in the regions that switched first and happen to use C61 and C62 will need to retune - see 2013 - post-switchover changes to Freeview transmission frequencies | - independent free digital TV advice .

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Briantist's 38,908 posts GB flag
Monday, 27 February 2012

3:35 PM

Jamie Skinner: Ofcom can't stop interference from LTE happening, it's a radio signal and Ofcom does not have the ability to re-write the laws of physics.

However, as detailed above in the article, Ofcom is providing mitigation by requiring filters to be provided on the transmitters and requiring the 4G licence holders to provide filters for the very small number of homes that will require them AT NO COST to the householder.

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Briantist's 38,908 posts GB flag
Wednesday, 7 March 2012
Michael Moore
9:40 PM

I cant believe this hasnt been a big story! I bought a freeview box thinking it would save me money, ive spent the last 3 months changing my whole system thinking something wasnt working right! Ive had two different companys check it and none of them could tell me what ive just read! Why was this never made big during the big switchover? We pay pay pay! And what for? I thought virgin media was a rip off! Joke!

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Michael Moore's 1 post GB flag
Thursday, 22 March 2012
mr p lees
7:52 PM

please could anyone tell me if there are any 4g transmitters in the chesterfield S40 2HF area. thank you

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mr p lees's 1 post GB flag
mr's: mapM's Freeview map terrainM's terrain plot wavesM's frequency data M's Freeview Detailed Coverage
Dave Lindsay

8:20 PM

mr p lees: If there are, then they are operating illegally as the licences haven't been auctioned yet.

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Dave Lindsay's 5,724 posts GB flag
Sunday, 1 April 2012
Paul Quinn
11:21 PM

Any ideas why most of my channels are breaking up at all times of the day? The only channels a really watch are film4 and ITV4 and the majority of the time they are both virtually unwatchable with pixalated, jumpy picture and stop-start sound. The box is a pretty good one with a hard drive but the problem existed long before I bought this newer box. I'm also about as technically minded as a housefly so any technical jargon will pass through my ears at as yet undiscovered speed!!

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Paul Quinn's 4 posts GB flag

11:43 PM

Paul Quinn: There are three main causes of this happening. (1) Weak signal caused by receiver tuned to the wrong transmitter, or the aerial is inadequate,faulty, or is in the wrong position for the best reception. (2) Interference from electrical equipment, engines or other transmitters. (3) Signal too strong, especially after a high power transmitter enters service and a high gain aerial or booster is in use. If you supply your postcode a check can be made of the predicted reception at your location, then further advice can be given.

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KMJ,Derby's 1,811 posts GB flag
Monday, 2 April 2012
Paul Quinn
9:50 PM

KMJ - thanks for your swift reply. My postcode is SN139LT

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Paul Quinn's 4 posts IT flag
Tuesday, 3 April 2012
Mike Dimmick

1:27 PM

Paul Quinn: At that location, the most likely transmitter is Mendip (BBC Points West, ITV1 West Country Tonight). Other possibilities are Oxford (BBC Oxford News, ITV1 Meridian Tonight), Rowridge (BBC South Today, ITV1 Meridian) or the Corsham relay. Corsham transmits the same programmes as Mendip, but only carries the three PSB multiplexes.

My guess is that the aerial points to Corsham, in which case you should have it moved to point to Mendip. It might be necessary to change the aerial for one of a different group, or a wideband.

If the aerial does point to Mendip, or those are the transmissions the box has stored, you would have had to retune last Wednesday when some services changed frequencies. This is always an opportunity for the naive tuning algorithm to store the wrong services, particularly in high-pressure conditions like we had last week (signals travel further in those conditions, meaning a distant unwanted transmitter can be stored rather than the desired one). The power level of two of the multiplexes was also increased, which could possibly mean the input level is now too high if it was pretty close before.

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Mike Dimmick's 2,486 posts GB flag
Wednesday, 4 April 2012
sue lovell
4:28 PM

since switchover I have retuned and everything is perfect except that when I video a channel and play it back it now comes with bright red faces why

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sue lovell's 1 post GB flag
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