UK Government To Offer Free TV Filters For 4G Interference 94
judgecorp writes "4G services could interfere with terrestrial TV in the UK, so the government plans to offer one free filter for every household affected by the issue. The analysis suggests that 2.3 million households could be affected, but many of those have cable or satellite TV, so the plan might only need a million filters (each household only gets one, even if they have many TVs)."
Re:Could? (Score:4, Informative)
Re:Could? (Score:3, Informative)
> Either it does or it doesn't
Utter rubbish.
It depends on so many things. Most importantly the relative strength of the Interfering signal compared to the wanted signal, but ultimately it depends on how well engineered the TV is in its ability to reject unwanted signals. Most TV's are woeful in this respect.
frequencies used by existing equipment (Score:5, Informative)
For a few more months in the UK analog TV will use 470-862MHz
The last few analog transmitters will soon be switched off,
the replacement digital transmitters will just use 470-790MHZ.
806-854MHz was auctioned off in 2009. 790-806MHz may be used for other tings in areas where it is not used for digital TV.
The worst case scenario for TV interference is roughly this.
Someone's house is on the edge of the coverage area of a digital TV transmitter which is on the highest multiplex frequency. They are 35miles from the transmitter and have a big TV antenna on a twenty foot pole on the chimney with a wideband preamp on the pole.
The TV signal is just barely strong enough to give a picture and only freeze occasionally when a pigeon flies in front of the antenna.
The TV signal is 8MHz wide ending at 790MHz.
A mobile internet base station push out 100 watts is installed 100 meters away from the house using frequencies starting just 16MHz higher at 806MHz.
In terms of power the mobile internet signal might be 70dB stronger, that's ten million times the received power.
The base station signal is strong enough that it overloads the masthead preamp. It dosn't even matter if the TV decoder can handle a massive signal close to a very weak signal, (and it probably can't) because the preamp is clipping and the weak TV signal is lost before it even gets to the TV.
In theory with good planning will mitigate this considerably.
In practise vast amounts of existing TV equipment is specifically designed to receive and amplify the frequencies that have been sold oof for other uses.
Mobile applications need lots of base stations close to the users.
Inevitably lots of people will have a base station on a tall building that they can see out of the window in an area where the TV transmitter is twenty miles away.
Re:Could? (Score:5, Informative)
The issue with interference isn't always due to primary band spectral overlap.
If a high gain receiver is trying to receive a small signal within a wide bandwidth that contains other much higher power signals, then the receiver can be saturated by the non-desired transmissions - even though it isn't in the same narrow frequency band as the desired signal. This could happen to someone that lives next door to a 4G tower, while trying to receive a signal from a distant TV transmission tower. (Again, it's possible to design receivers to resist this, but most cheap TV receivers won't need to be, and thus engineers probably won't bother.)
A secondary problem is side-band interference that occurs when the out-of-band components of a high power interfering signal are large enough relative to the desired signal to cause direct in-band interference. These out of band harmonics and side-bands are reasonably well suppressed below a given threshold relative to the carrier - eg. 60dB below the carrier. However, if the interfering transmitter is next door and its signal into the receiver is significantly higher (eg. greater than 50dB higher than the desired signal), then the signal to noise ratio of the desired TV channel will be insufficient for 'clean' reception, and interference will be visible.
The same issues occur when your house is 'next door' to a high power local TV transmitter and you're trying to receive a program from a much more distant channel in a neighbouring band. But, that particular issue has been worked around since the dawn of TV broadcasting. OTOH, mobile phone towers are much more densely packed and have tighter beams that can be electrically steered to point right past (and thus be received by) a given TV antenna as it 'follows' the phones it's transmitting to.
Re:"Free" ? Who pays for them? (Score:4, Informative)
If the government gives them out "free", it means that the taxpayers pay for them.
Why not force the 4G providers, who are causing the interference, to foot the bill . . . ?
£180 million is top-sliced from the 4G auction; the government will make up the rest, if any. They probably bring in more money for the taxpayer that way, than if the bandwidth came with an unknown liability,.
Re:Could? (Score:5, Informative)
Re:Could? (Score:5, Informative)
Even if you are have no band overlapping, if you are close enough to the transmitter the out of bands harmonics might be strong enough to go through your receiver.
I've had this once while landing at Toronto City Center Airport, right next to the CN Tower and its FM transmitters. On final we suddenly had some stupid Radio show bleeding over the Tower Frequency and I'm quite sure there isn't any Frequency overlapping between FM radio and aviation bands. But I also suspect their might have been an issue with the Receiver. Anyway, it illustrates well that you don't need frequency overlap to have annoying interference.
(and we narrowly avoided our desire to crash into the transmitter, Nickelback was playing).
Re:Only just gone Fully Digital - then this? (Score:4, Informative)
UK governments don't give a stuff about you and me - they only care about the money they can make from selling spectrum to big business. If that means the new use of the spectrum will cause interference to our TV viewing ... weeeell, thats just collateral damage.
Also worth noting that Sky won't be affected. We've just had an inquiry that shows how in bed the political class is with Murdoch, and the BBC is always under attack.
Before Freeview (DTT), we had an over-the-air subscription based service (ondigital, later itvdigital). People thought "digital tv == subscription"
Greg Dyke (DG of the BBC at the time, hounded out for being in charge of a reporter than said the evidence to invade Iraq was "sexed up" -- later proven completely true) made a bold play to push through Freeview when ITVDigital went bust, which got DTT receiving equipment without CAMs, which meant the Murdoch lot couldn't later argue for the BBC to move to a subscription basis.
He paid the price for this defiance, and they're slowly trying to get rid of freeview