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> News >

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 by 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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M
MikeB
Tuesday 9 July 2013 10:14PM Peterborough

Lynda Eves: Firstly, there are no 4G tests anywhere near KL, so I'd discount that factor. On the other hand, North Norfolk is well-known to be a bad area for Freeview, owing to various factors (my parents-in-law live in North Norfolk).

The first thing to look at is your aerial - where does it point? (and look at those near you as well). Assuming you want more than just the basic channels, your not using KL's transmitter, but its parent at Tacolneston, at least in theory. On the other hand, the terrain plot comes up with something in the way about 4 miles away from you for Tacolneston.

The Digital UK Tradeview actually comes up with Waltham as your most likely transmitter, which recently had a retune, which might have upset a previously doable but marginal reception. Frankly, you've got a lot of possibilities, and most of them a fair distance.

OK, once you know where the aerial is pointing, what RF channel is the TV on? KL is 40, Waltham is 49, etc - and hopefully you'll find a channel which has enough signal strength to get a decent signal.

link to this
G
george
Wednesday 14 August 2013 10:20PM

I live in watford and we had problem a few months ago with reception for about 1 month. Then everything worked perfectly for about 3 months then last week or so started getting problems again. Not all day but suddenly happens that we lose reception completely for a couple of hours then it comes back. Any suggestions ?

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J
John Anderson
Monday 19 August 2013 10:22PM

Hi

I live in Sedgley on the Western Side of the ridge - I can see the Wrekin transmitter from my house.
In recent days I have started to recive a degraded Freeview signal on my Panasonic Television.
Is there a problem?

link to this
P
pete
Sunday 8 September 2013 10:23AM

We have a campervan using a status multi directional aerial and naturally travel around what can we do regards signal loss and interference

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