DTT, Digital Terrestrial Television, Freeview, Top Up TV, Digital Switch Over, Advice

DTT Digital Terrestrial Television - THE FUTURE OF TELEVISION!

This short page was prompted by a question from MDS975.co.uk reader Peter W Robinson who asked:

"I live in a valley. Please can you tell me when we will have a transmitter able to transmit Digital TV to our homes - other than BBC which is very good. Of course we could get a dish for sky etc. but I believe that sooner or later we should be able to receive the Freeview signals from ITV and other channels. Please let me know what is holding up this work?"

In essence the answer to the question is this:

INTRODUCTION - How Analogue Television Has Been Arranged

The five 'ordinary' analogue television channels, BBC1, BBC2, ITV1, Channel Four (or S4C) and FIVE are broadcast on the UHF band (Ultra High Frequency radio band) using the analogue PAL (Phase Alternate Line) colour standard in the UK on frequencies between 471 MHz and 847 MHz which are divided into 'channels' numbered from 21 to 69. There have been over 900 television transmitter masts constructed jointly by the BBC and IBA between the 1950's and 1990's (and latterly some further small relay masts installed by Crown Castle and NTL). Almost all of these transmitting stations transmit the four terrestrial TV stations; BBC1, BBC2, ITV1 and Channel Four/S4C. Each TV service having being carefully allocated a specific 'UHF Channel' number to be transmitted on from the mast. Eg the Winter Hill mast in Lancashire transmits on these channels:

BBC1 on UHF channel 55
BBC2 on UHF channel 62
ITV1 on UHF channel 59
Channel Four on UHF channel 65

Some 50 of these masts are designated as 'Main Stations' and transmit at high or very high powers in the order of 20,000 to 1,000,000 Watts effective radiated power. These 'main stations' reach the majority of the UK population. The remaining population has to be served from hundreds of medium or low power relay transmitters using powers typically in the order of between 2 Watts to 10,000 Watts. In this way 99.6% of the population of the UK is served with four channels of analogue TV.

Due to the fact that the UHF television band was originally planned in the 1960's to accommodate four television services it was a challenge for the DTI, ITC , NTL and BBC to factor in a fifth television service in the early - mid 1990's in the form of Channel Five Television. Because of the limits of radio spectrum space available FIVE TV, as it is now known, could be allocated a total of (only) 47 transmitters and so reaches around 80% of the UK population. Some of Five's transmitters are at the same or similar power as the other four analogue channels, but there are many that are at lower power; for example FIVE TV is transmitted from Winter Hill on UHF Channel 48, but at much lower power than the other four TV services so as not to cause interference to existing transmitters elsewhere. This is also the case at other FIVE TV transmitters where lower power must be used to avoid interference to viewers of other stations. Powers for FIVE range from 33 Watts to 1,000,000 Watts.

THE MOVE TO DIGITAL TERRESTRIAL

The FREEVIEW DTT service was established jointly by the BBC, Crown Castle International (the transmission service provider) and SKY to bring Multi-Channel television reception to a wider audience and via the existing infrastructure of terrestrial television masts that could be recieved through standard rooftop aerials.

FREEVIEW digitally transmits multiple television services in "Multiplexes"* The BBC channels BBC1, 2, 3, 4, BBC News 24, CBBC, CBeebies and BBC Radio etc. are all transmitted together in the BBC's dedicated multiplexes; ITV1, ITV2, ITV3, ITV News etc are lumped together into another multiplex and other TV services such as Channel Four, FIVE, Sky News etc arrive in further multiplexes. Many more TV and radio channels are available by this method than would otherwise be possible by traditional analogue methods. A further service, in addition to FREEVIEW, is also available via the normal rooftop television aerial and set top box called TOP-UP-TV. Top Up TV is a pay to view service providing a number of so called 'premium' channels and is packaged into further multiplex space and requires a viewing card and a set top box that is equiped with the necessary viewing card slot.

Many of the main terrestrial television transmitter sites, along with some of the larger relay transmitter sites, already carry DTT, but currently are at lower power due to the severe lack of frequencies/channel space available in the UHF televison band between channel 21 and 69. The vast majority of small relay transmitters (of which there are hundreds) cannot carry FREEVIEW or TOP-UP TV at all at present, again due to the severe lack of frequencies/channel space. This lack of spectrum space is what is holding up the expansion of DTT at the moment.
Around 70 percent or more of the population are within reach of DTT but very much less of the geographical area of the UK is within covered by DTT signals. This is because for both economic reasons and the need for radio spectrum efficiency, television signals must be concentrated on areas of significant population. Even with the 99.6% population coverage of the analogue televison network there will be vast geographical areas that do not receive coverage - but this is generally not a consideration if there are only one or two households in a sparsely populated area. The latter analogue TV relays to be commissioned at great expense only provided TV reception to populations of only one or two hundred households. With the current DTT network it was relatively easy to get coverage to densely populated areas with a just few dozen transmitters, but to bring coverage to the last 30 or 40 percent of the population requires many hundreds more transmitters to be built - incredibly expensive of course - but the real constraint to DTT currently is that there simply no spare frequencies whatsoever available for them to operate on.

It will not be until the current ANALOGUE transmitters (UHF PAL Colour) of BBC1, BBC2, ITV1, Channel Four and FIVE are switched off (around 2008 - 2010) that DTT (FREEVIEW and TOP-UP TV) will be able to be transmitted from all necessary low power relay transmitters, and at full power from the main transmitter masts, to provide the 99+% coverage currently available via ordinary analogue TV today. The switching off of analogue television is, however, a politically a hot potato because millions of people could be left without any television and may be very unwilling to pay for a set top box and maybe more or a necessary aerial upgrade or adjustment.

It will not be until analogue transmitters are switched off that DTT (digital Freeview and Top Up TV) can expanded to all the required transmitter sites and with the necessary full strength signals.

It is rather a chicken and egg situation. Until analogue is switched off there can be little further roll out of DTT, but without any DTT reception in many areas why would many viewers buy a DTT set top box that can receive no pictures?

It is worth noting, however, that ITV are considering quitting their contract with BSKYB and thereby saving millions of pounds. The BBC, of course, did this a year or so back and hired time on a different satellite (in the same orbit as the ones used by BSKYB so that viewers can still receive all the BBC channels Free To Air without having to pay Mr Murdoch's BSKYB for the privilege). If ITV quits BSKYB then they could also hire time on the same satellite that the BBC is now using to transmit its television and radio services. The ITV1, 2, 3and 4 channels would then not be encrypted as they are today on SKY, so viewers will not need to pay for an expensive "Viewing Card" to decrypt the channels and make them watchable. Channel Four and FIVE may well follow - also unencrypted. If this happens then there are embryonic ideas for the BBC, ITV Ch4 and FIVE to form a new bouquet of TV channels (probably) called FREESAT which will be very much like FREEVIEW but transmitted via satellite rather than the network of terrestrial transmitter masts.

*NOTE: A MULTIPLEX is a special method of digital broadcasting in which the a single transmission can be used to combine and transmit several television services. The use of sophisticated digital compression techniques, such as MPEG4, enables many television and radio services to be accomodated (squashed into) a single multiplex. Several multiplexes will be used from each television transmitter to bring a multitude of channels to the viewer/listener. A multiplex is broadcast on a single UHF channel just like an analogue TV station, but using digital technology. This digital technology uses very clever compression techniques to shoe-horn in five or more television services into the space normally occupied by a single analogue station.

ANALOGUE TELEVISION CONFIRMED TO BE SWITCHED OFF BETWEEN 2008 and 2012

TV viewers in Wales, the Border and West country ITV regions could switch off their analogue signals within four years under a UK-wide timetable.

Media regulator Ofcom has said the UK can only be fully digital by 2012, the UK Government's target date, if it switches over region by region. The switchover would need to begin in 2008.

The government said no firm decision on the timetable would be made until consumers' interests were protected. The phasing in of a digital-only service would end with the analogue signal being switched off in the Channel Islands in 2012. Currently, 60% of households in the UK have digital TV. Digital terrestrial signals reach 73% of UK households, but a significant increase in coverage is not possible until analogue is shut down.

Ofcom's proposal, published on Wednesday, has been submitted to the Department for Culture, Media and Sport and the Department of Trade and Industry. In a statement, Ofcom said: "The actual year in which switchover begins and regions subsequently convert remain a matter for government to determine as part of its overall switchover policy. "Ofcom remains committed to the earliest practical switchover policy, while recognising the need to take proper account of the interests of viewers and other key parties."

To continue to receive television after the switchover from the analogue signal, viewers in digital-only regions will have to connect all their TV sets to a digital TV service, via Freeview, cable or satellite. In most cases, that would require them to buy a receiver box and possibly to upgrade their aerial.

Each region is expected to take six months to convert, giving households time to switch to digital cable, terrestrial or satellite.
Which? has warned the proposed timetable will force consumers in some regions to switch against their will within three years with costs of up to £300 - or lose out on TV altogether.

A Highly Technical Project

Allan Williams, senior policy advisor for the consumers' rights body, said: "The government must keep its promises and should not switch off analogue TV unless the digital TV option is available and affordable to all. "Vulnerable consumers, especially the elderly and socially disadvantaged, may not want the extra channels and the burden of the cost that digital will inevitably bring."

A statement from the UK Department for Culture Media and Sport said it wanted to make sure some groups were not left behind by the switchover to digital. The statement read: "Digital switchover is a huge, complex and highly technical project."

"Switchover is very much work in progress and this is a useful indicative analysis of the best way to switch to digital TV region by region."

"We will make no firm decisions on the timetable until we are satisfied that the interest of all consumers, including the most vulnerable, are appropriately protected."

FROM BBC NEWS (9 Feb '05):

DIGITAL SWITCHOVER BY ITV REGION

HTV Wales 2008

Border 2008

West Country 2008

Granada 2009

HTV West 2009

Grampian 2009

Scottish TV 2009

Central 2010

Yorkshire 2010

Anglia 2010

Meridian 2011

Carlton/LWT 2011

Tyne Tees 2011

Ulster 2011

Channel 2012

NEW NEW NEW

TECHNICAL INFORMATION

WHAT UHF CHANNELS WILL BE USED FOR D.T.T.POST DIGITAL SWITCH-OVER

It will be all change post digital switch over, not only will there be no more analogue television, but there will be a new arangement for the allocation of UHF channels used in the UK for broadcasting.

Our corresponent, Martin Watkins, has complied one of his typically marvellous transmitter lists which you can download HERE.

(ITU UK DTT allocations - compiled by Martin Watkins, November 2006 - version 9)

HOW TO RECEIVE FREE DIGITAL TELEVISION

Around thirty channels of Digital Television can be received free of charge via an ordinary roof mounted tv aerial by about 70 to 75 percent of households (as of end 2005) with the FREEVIEW service using an inexpensive Set Top Box (STB). I can recommend the GOODMANS GDB6 as being an excellent unit, not only is it sensitive to weak signals, unlike some other models (this means that I receive a multiplex that officially I should not be able to), but it is very inexpensive at less than £40 typically. The GOODMANS GDB6 is also very easy to install taking less than 5 minutes to auto tune to all the available multiplexes, and simple to use day to day.

The Excellent GOODMANS GDB6 Freeview Receiver (Set Top Box)

http://www.goodmansdigital.co.uk/Digital_Freeview/GDB6.htm

The 75 percent coverage of FREEVIEW will not be able to expand significantly until the analogue transmitter begin to be shut down from 2008 onwards.

A SUITABLE TV AERIAL
Apart from a set top box like the Goodmans one shown above, viewers will need a suitable tv aerial. In many cases an existing tv aerial will be sufficent; As long as existing analogue pictures are clear and free from snow, noise and interference (and that DTT - digital television - is transmitted from the transmitter that the aerial is pointing towards) then viewers could reasonably expect to be able to receive the many digital channel available from FREEVIEW and Top Up TV. If the pictures are a bit snowy and noisy on analogue (indicating that the aerial is poor anyway) there is a good chance that digital reception will not be possible and that an aerial upgrade will be required. Additionally if the DTT multiplexes are transmitted in different UHF channel groupings than the local analogue channels (more about this below) it may be that the existing aerial may need to be replaced with an aerial of a more suitable group or a 'wideband' aerial (more below).

MORE ABOUT AERIALS AND UHF CHANNEL GROUPINGS

When considering digital television the viewer must also consider the aerial. Although DTT is transmitted at much lower powers than traditional analogue TV (about 20dB less) digital television receivers only need signals of about 20 dB less than analogue sets to work properly. HOWEVER with analogue, if your aerial is producing a weak signal the pictures on the viewer's TV will just be a bit weak - i.e. snowy, grainy, noisy. NOT SO with digital television! - If the signal produced by the aerial is a bit too weak then the pictures will simply not appear on the screen at all and the viewer will end up with a black screen. Once the signal threshold has been reached or exceeded then the perfect digital pictures will return - With digital it is an All Or Nothing situation - there is no snowy analogue 'half way house'!

An aerial that is in good condition, not too old and damaged by the crows is essential, as is good quality (NO) VERY HIGH QUALITY screened digital,satellite grade 75 ohm coaxial downlead cable. The aerial must also be of the correct GROUP for the digital signals (see below) and accurately installed and aligned with the appropriate transmitter.

When analogue 625 line colour television was introduced to the UHF band in the 1960's each transmitter site was allocated a group of four channels to transmit the four anticipated tv stations (BBC1, BBC2, ITV and The Fourth Channel). The four UHF channel groupings were close together and repeatedly used at hundreds f sites all over the country to make efficient and organised use of the limited radio spectrum available. Due to the laws of physics aerials can only work effectively over a limited range of frequencies (channels). For this reason The UHF band, which covers a huge range of frequncies from the lowest at 471MHz (UHF Cchannel 21) to 847MHz (UHF channel 68), was split up into three "GROUPS" or "AERIAL GROUPS":

GROUP A aerials can work efficiently between u.h.f. channel 21 to u.h.f. channel 37
GROUP B aerials can work efficiently between u.h.f. channel 35 to u.h.f. channel 53
GROUP C/D aerials can work efficiently between u.h.f. channel 48 to u.h.f. channel 68

If a grouped aerial is used to try to receive an 'out of group' transmission poor reception will usually result as there will be very little 'gain' and the direction properties of the aerial may also be lost - instead of the main pick up lobe facing directly in front of the aerial, as it should, the lobe will be distorted and face off at some unwanted angle.

More recently new aerial groups have been introduced that cover wider bands, the gain and directional characteristics may be slightly less than the above equivelents, but they are designed to work with larger groups of channels properly:

GROUP K - 21 to 48
GROUP E - 35 to 68
GROUP W - WIDEBAND - All Groups from 21 to 68 (The gain of these aerials may not be quite as high as those for the grouped aerials, A, B, C/D)

GROUP W Aerials have become much more frequently used with the introduction of DTT where wide spacings of u.h.f. channel groups are used at the transmitter. It is not always necessary, however, to use a WIDEBAND aerial simply because one is trying to receive digital television, many transmitters have managed to squeeze in the DTT multiplexes in groupings that fall within the existing analogue grouping.

As an example, in the Sutton Coldfield transmission area five of the six digital multiplexes fall within the original analogue grouping, except the highest multiplex, MUX-D which is on u.h.f. channel 55, channel 55 just falls outside the GROUP B Aerial grouping! Maybe a group B aerial would work okay, but maybe it would be better to install a Wideband aerial just in case? But then the gain of a wideband aerial in the B group part of the spectrum may be a little lower than the gain of an equivalent B group aerial. Difficult

Sutton Coldfield's channel groupings:

Analogue: BBC1 = ch 46   BBC2 = ch40 ITV = ch43 Channel Four = ch50 Five = ch37(Lichfield)    : U.H.F channels 37, 40, 43, 46 and 50 fall within AERIAL GROUP B.

The DTT multiplexes are MUX1= ch41 MUX2 = ch44 MUX-A = ch47 MUX-B = ch51 MUX-C = ch52   MUX-D = ch55

Winter Hill's channel groupings:

With Winter Hill it's much easier - all channel groupings fall within the C/D Aerial Group:

WINTER HILL Analogue TV : Channels BBC1= ch55 BBC2=ch62   ITV1=ch59 CH4=65 FIVE=48 (very low power)
Digital TV: MUX1=ch56 MUX2=ch66 MUXA=ch68(slightly lower power) MUXB=ch67 MUXC=ch60 MUXD=ch63

Additionally it is thought that free digital television channels may become available via the a FREESAT service which may be launched independently by the BBC and ITV during 2006.

[Other methods are via SKY and paid subscription to the SKY satellite service or paid for monthly subscription to a local cable company, if there is one.]

LINKS TO HELPFUL WEBSITES:
(All links will open in a new window)

www.aerialsandtv.com - Aerial installations, theory and practice

www.atvcircuitsandservicemanuals.co.uk - TV service information

http://www.wrightsaerials.tv/ - Bill Wright's aerial installers website

DIGITAL TV GROUP - Information for the public and trade including - RECEPTION POSTCODE CHECKER

FREEVIEW - The official Freeview website

BBC FREEVIEW ADVICE - advice from the BBC about digital television

GOODMANS DIGITAL UK - Manufacturer of FREEVIEW Set Top Boxes and other entertainment equipment

DIGITAL - Get Set For Digital !

OFCOM - Ofcom is the broadcasting regulator and this page offers advice on the digital switchover

UK-FREE-TV - general digital infomation

DTT-TX-INFO site - Information about the digital tv transmitters

SKY TELEVISION - Paid-for subscription digital television via a dish

BBC NEWS (General)

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