www.uncletony.co.uk

Satellite TV Stuff

uncletony created this page to give a basic introduction on how Satellite Television works.

  • The first section of this web page will explain how to get Satellite TV in the UK - either by paying a monthly subscription to Sky or by paying nothing at all (except for the receiver box and dish) for programmes from FreeSat or FreeSatfromSky.
  • The rest of this page is a semi-technical introduction to satellite TV, how it works and some stuff about scrambling.

*** Just read the bits that interest you! ***


If you wish to make suggestions. correct problems and/or errors, offer advice or simply want to have a chat then please e-mail me here.

 

What is the Digital Switchover?

By 2012 the UK will have completed the change from analogue to digital television. This is known at the Digital Switchover (click here for more details) and is being done region by region following a government timetable. When it is complete viewers will have three system options to get their favourite channels. These are Freeview (the land based-terrestrial service) which needs a normal TV aerial and Satellite TV which uses a dish pointed at a cluster of satellites in space. A third option, only available in certain areas, is Cable TV.

If you live outside a Freeview coverage area (click here to check using your postcode) and cannot see the extra programming available, an alternative is to get a satellite TV system.

Read on to learn what you need to do ....


Firstly, a short introduction:
TV and radio programming aimed primarily at the UK comes from a group of satellites located at 28° east of South. They are called 'Astra-2A, Astra-2B, ..., etc, and EuroSat'. The main provider of satellite television for the UK is Sky and virtually all their channels are scrambled. To unlock Sky channels a dedicated receiver-box and a special viewing card are needed. The viewing card contains special electronic codes which unlock the channels you pay for each month. Getting these Sky programmes can be expensive (starting at about GBP17+ a month).

What can you get for free from Satellite?
Sky is primarily a subscription-based service offering several hundred channels of TV and Radio. The actual monthly cost depends upon the subscriber's selection of channels and equipment. A special 'viewing card' is required to be inserted into a dedicated Sky receiver box to unscramble the programmes subscribed to. However some channels are not scrambled and can be viewed on a standard satellite TV receiver box (often called a Free-to-Air receiver) connected to a correctly positioned dish.

What about Freesat and FreesatfromSky?
Freesat is a joint venture between BBC and ITV to provide free TV viewing across the UK without the need for any subscription charge. All you need to do is buy a receiver and and have a dish installed (either by youreslf, a friend or a recognised aerial company). A dedicated Freesat receiver has a comprehensive Electronic Programme Guide (EPG) built-in making programme selection for up to 7 days ahead very easy.

FreesatfromSky operates in a very similar way, but requires the use of a dedicated Sky box and a 'viewing card'. The FreesatfromSky service requires a one-off payment for the installation of receiver and dish. This gives all the free channels plus a selection of subscription channels for a few months. If the additional channels are NOT cancelled within the specified time period the viewer will have to give at least 30 days notice to cancel the subscription. Viewer beware!

What about HD TV channels?
HD programmes are only available (at the moment) via satellite. Freeview HD channels are expected to become available during the latter stages of the Digital Switchover roll-out. The BBC and ITV programmes are free to view. Freesat HD compatible receivers are available to buy (starting at about GBP95). Sky offers a wide selection of HD programming but a special HD receiver and an additional subscription is necessary.

 

BBC HD logo ITV HD logo



Astra-2D footprint
Astra-2D footprint by courtsey of SES-Astra

 


Sky logo

FREESAT FROM SKY
Call Sky on 08442 410 595

For more info on programme choice, visit www.freesatfromsky.co.uk
and read the Q&A section.


Freesat logo


Call Freesat on 0845 313 0052

 

IMPORTANT - If you have your own Sky Digibox, dish and LNB and can install it yourself (or have a mate to do it), then ask Sky to send you a FreesatfromSky viewing card - a modest fee may be payable. Or buy a Freesat receiver and enjoy all the free channels and free HD !

 

 

uncletony created this part of the page to give a general introduction on how Satellite Television works.


Satellites in Space    

TV broadcast satellites are placed in orbit directly above the equator at a height of about 36000km. They travel through space at the same speed the earth's rotation - so to us on the ground the satellite appears to be stationary. This is known as a geo-synchronous (or geo-stationary) orbit.

Ground controllers fire on-board jet thrusters occassionally to keep the satellite in the specified position in space. This is the major factor in determining the 'life' of a satellite.

In Europe the orbital location of a satellite on the Clark Belt is given by the number of degrees to the East or West of due South (for example: Astra 1 = 19.2°E, Hispasat = 30°W). This is the Azimuth.



representation of the Clark Belt
The Clark Belt viewed from northern Europe

The idea of geo-stationary satellites was first suggested by Arthur C Clarke in an article written for Wirless World magazine in October 1946.
The region in space occupied by these satellites is commonly referred to as 'The Clarke Belt'

Getting signals to and from the Satellite

Television and radio programme signals are sent from the various originating studios to an Earth up-link station. From there the gathered 'bouquet' of programmes is transmitted into space using a dish aimed at the orbiting spacecraft. This is known as the 'up-link'. The frequency is about 14GHz (in Europe)

The satellite receives these signals, amplifies them and transmits them back towards earth on a different frequency. This work is done by a transponder.
This 'down-link' operates at about 11GHz (in Europe), in the so-called Ku microwave band).

A group of satellites in the same orbital position (such as Eutelsat's 'Hotbird') may have a combined total of more than 70 transponders. A transponder rebroadcasts 1 analogue TV channel or as many as 14 digital TV channels (this depends on the digital compression techniques used:- lower compression = less channels = better pictures).

This kind of broadcasting is known as DTH (Direct-to-Home broadcasting).

Each satellite has a massive array of solar cells. Some satellites are cube-shaped and have huge wing-like solar cell arrays extending from the main body, while others are cylindrical and have their entire surface coated with solar cells. The cells convert sunlight into electricity to operate the satellite, providing power for the transponders and to maintain the charge on the standby batteries for the times when the satellite is in the shadow of the Earth.

Astra Logo ( (with acknowledgement to SES Astra) eutelsat logo Swiss PTT up-link station
Up-link station at Leuk, operated by Swiss PTT

The satellites used for radio and television broadcasting are not usually owned by the broadcasting companies.
Broadcasters lease the technical facilities from the satellite owner. In Europe the two major satellite providers are Eutelsat and SES-Astra
.
The earth stations required to send the programmes up to the satellite (called the 'up-link') are provided by a variety of organisations in many many different countries. Some of these are commercial organisations (eg BT in UK) and some are government agencies (eg national PTT authorities).

 

The Footprint
Satellite Foot-Print (with acknowledgement to SES Astra)


This is the actual signal strength map (or Footprint) of the Astra 1G and 1H satellites (as published by the owners of the satellites, SES-Astra). Both 'birds' are located in the same orbital position in space at 19.2°E.

The antenna on the satellite directs the signal down to a specific land area.
Just as the beam from a flashlight gets wider and weaker over distance so does the satellite radio signal.

Contour lines on the map show the required dish size for satisfactory all-weather reception.

Note that these satellites have a signal beam dedicated to covering the Canary Islands. This arrangement is known as a 'spot-beam'.

 

 

Tuning into Satellite TV and Radio ...

To tune in to satellite TV some specific receiving equipment is needed.

The most obvious item is the dish. The dish is the antenna (aerial). It works like a curved mirror to collect, reflect and concentrate the radio energy from the satellite and focusses it into the throat of the LNB (Low Noise Block).

The LNB amplifies these very weak signals and converts them to a lower frequency (from about 11GHz down to about 2GHz), the so-called intermediate frequency. This signal travels along the coaxial cable to the Receiver unit in the home. It is very important to use the correct type of coax cable - ask your supplier for CT-100, or better.

 

typical single-output LNB
Typical single-output LNB

The Receiver (often called the set-top box, STB) performs all the electronic signal processing that is required to recover the TV signal. In addition it sends power and control signals up the cable to the LNB. The Receiver is connected to the TV set either by an antenna (aerial / RF) lead or SCART cable. Operation of the receiver and channel selection is normally done with an infra-red remote control unit.

This basic principle of getting the satellite TV signal is the same whether an analogue or digital system is being used. However, the electronic processing of digital and analogue signals is very different indeed.
Digital signals comply with the DVB-S (Digital Video Broadcasting - Satellite) protocol. Look for the DVB logo. For an analogue signal, the signal strength is very important, but for digital reception as much care must be paid to maximizing signal quality (the higher the quality number the less bit-rate errors the receiver will have to cope with).

 


Satellite TV receive set-up

More Dishes, More Satellites

For a greater choice of programming it is possible to 'look' at several satellites. This can be done by using a motorized dish or a combination of several fixed dishes and LNB's.

 

To use multiple dishes a simple switching system called DiSEqC (Digital Satellite Equipment Control™ - developed by Eutelsat) is all that is needed, but the receiver must be DiSEqC compatable. The DiSEqC switch is usually fitted near the dishes and a single cable feeds to the Receiver. The Receiver box sends control signals along the cable to the DiSEqC switch to automatically select the correct combination of dish/LNB and satellite.

Upgraded versions of the DiSEqC protocol allow for control of motorised dishes (DiSEqC 1.2 and 2.0).

For detailed spec of DiSEqC™ protocol go here

 

Two dishes and Diseqc switch

A different type of motorized system is the horizon-to-horizon (H-H) method. Here an electrically operated screw-jack pushes and pulls the dish which pivots on a special mounting bracket. This makes the dish accurately follow the position of the satellites along the Clark Belt. Receivers incorporating this type of motor drive will usually have 'Positioner' included in the name/description.

For even greater flexibility LNB's are available with single, dual, quad or octo (8) outputs. Each output is totally independent from the others. This allows multiple receivers (living room, bedroom, kitchen, etc) to connect to a single dish/LNB.

If 'looking' at two closely spaced satellites (eg Hotbird [13°E] and Astra-1 [19E°]) it is possible to use one dish and two LNB's mounted on a special extension arm. The dish and one LNB is focussed on the weaker of the two satellites. The second LNB is moved along the extension arm until a satisfactory signal from the second, stronger satellite is received (this picture shows a single output LNB 'looking' at Hotbird and a quad output LNB 'looking' at Astra-1 - note that one output from the quad LNB is not in use).

2 LNB's on a single dish arm

This is a view of uncletony's dish installation.
The garage roof is used as a base for the various dishes. The LNB's are connected to a 4-way DiSEqC switch. The output of the switch is a single cable connected to 'free-to-air' analogue and digital receivers.
The Sky (Astra-2) system is a completely separate installation for family entertainment.


uncletony's 5 dishes
uncletony's 5 dishes


4-way DiSEqC 1.0 Switch
Pole-mounted 4-way
DiSEqC switch

Pointing the Dish

To receive a strong and reliable signal in all weathers the dish must be pointed directly at the satellite.
Select a position where the path to the satellite is clear and unobstructed (for example a tree without leaves in winter will cause no problem - but in summer virtually no signals will get through to the dish).

"Pointing the dish" means setting the Azimuth and Elevation correctly.

  • Elevation is the angle between horizontal and the satellite in orbit on the Clarke Belt.
    (In the UK this ranges from about 21° in the far north of Scotland to about 27° in the south of England [for Astra 1]).

  • Azimuth is the position (east or west of south) where the satellite is located (19°E, 1°W, etc).

  • Skew (or polarization offset) is the final little tweak required to get the strongest possible signal from the satellite. Instead of having the LNB fixed vertically in it's holder, a few degrees of clockwise (right) or anticlockwise (left) twist from the vertical is applied to compensate for the position of the satellite being either east or west of due south (in the northern hemisphere). The skew applied in northern UK for Astra-1, 19°E, is 10° clockwise. This increases to 16.5° for viewing Astra-2 at 28°E

When setting up your dish it is important to take into account the difference between true North and magnetic North. This is called the Magnetic Declination (or Variation)

 

Download this useful FREE program from Pangolin Comms to easily calculate the Magnetic Variation at your location anywhere in the world.

 

Link to Pangolin, New Zealand

If you've got a dish you've gotta have this .... download SWMLink from Swedish Microwave. Among the many things it can do, this useful application is probably the best there is for calculating dish Az, El and Skew from any location on the globe for any satellite on the Clarke Belt. And best of all it's for FREE....

 

Link to Swedish Microwave site

To find your Latitude and Longitude go to www.streetmap.co.uk and enter your UK postcode.

Once the map is displayed then click on 'Click here to Convert/Measure coordinates...'.
Your location details will be shown in a new table.     Dead Useful!

 

Link to Streetmap web site

For worldwide locations go to www.heavens-above.com to find your Latitude and Longitude

Link to Heavens-Above web site

 

Introduction to satellite Transponders

Transponder diagram
Transponders are interleaved using opposite polarity

Adjacent transponders are transmitted with alternate polarity. This allows more transponders to be used within the frequency band(s) allocated to satellite DTH broadcasting. The LNB is capable of switching between signal polarity.

Each transponder on a satellite has a typical bandwidth of 27MHz.
A single analogue channel will occupy this whole space. Up to 14 compressed digital TV channels can be fitted into the same space.

Typical satellite analogue TV signal
Video signal is 6 MHz wide. Main Audio carrier is at 6.60 Mhz
Additional audio sub-carriers at 180kHz spacing are used for stereo TV sound, alternate languages and/or radio stations

Typical satellite digital (MPEG) signal
Symbol Rate represents the data rate (typically 27500Kbps) - see below.
FEC is the Forward Error Correction factor inserted by the broadcaster. The data stream can include TV, Radio and/or computer data.


Modulation

The analogue system uses FM (Frequency Modulation).

The digital system uses QPSK (Quadrature Phase Shift Keying) modulation.
This works by changing the phase of the In-phase (I) carrier from 0° to 180° and the Quadrature-phase (Q) carrier between 90° and 270°. This is used to indicate the four states of a 2-bit binary code. Each state of these carriers is referred to as a Symbol.

QPSK daigram
QPSK diagram showing how four different
binary codes can be transmitted

 

Introduction to Encryption (Scrambling)

The television and radio programmes which can be watched by anyone with a basic receiver are known as Free-to-Air (FTA).

Many broadcasters charge a subscription for their programmes, and t
o prevent unauthorized viewing the signals are scrambled (encrypted). There are several digital encryption systems - for example Cryptoworks, Conax, Irdeto, Mediaguard, Viaccess, etc. In Europe the majority of the few remaining analogue encrypted channels are beamed towards Scandinavia. These services use the MAC TV standard, and the scrambling system is Eurocrypt.

To unlock a channel the viewer needs a Receiver with a Conditional Access Module (CAM) that matches the encryption system being used. On payment of a fee the programme provider will supply the viewer with a viewing card containing special codes (called keys) to unlock only the subscribed channels. Copyright and other legislation normally does not allow the purchase and viewing of programmes in one country which are intended for another country (for example: it is not permitted for viewers in Spain to watch encrypted programmes 'aimed' at the UK by SkyTV).

Some Receivers are dedicated to one television network and one encryption system (for instance in the UK, SkyTV can only be picked-up on a receiver with an embedded (built-in) Videoguard CAM). In this case the subscriber's viewing card is linked electronically to one specific receiver.

Many Receivers are available with a common interface (CI). This is a single or double 'slot' into which one or more CAM's can be inserted. Once the CAM is in the receiver the necessary viewing card is inserted into the CAM.

The CAM has been designed to have the same physical format as a PCMCIA Card (which are extensively used in lap-top computers (Modems, etc)).

For the satellite enthusiast a wide range of experimental CAM's are available (Magic Module, Axas-II, Matrix Reloaded, Dragon, etc). Many reportedly operate on several of the encryption systems. Various models of these CAM's are advertised in hobby-related magazines.

There are a few Receivers on the market which have an embedded experimental CAM (so-called UCAS - Universal Conditional Access System). These Receivers usually have at least one additional slot for another CAM.

CAM - outside view

CAM- internal view
Conditional Access Module (CAM)
External and Internal views


Receivers with built-in hard disk drives are becoming very popular. When combined with the appropriate CAM and viewing card it is a simple matter to record any TV programme to disk ready to be replayed at a later date. Most have twin tuners which allows the recording of one channel while viewing another.

The Dreambox receiver operates very much like a computer. It uses an IBM 'Power-PC' processor and uses the Linux operating system. Because of the open access of Linux code many Dreambox enthusiasts create and modify software to continually improve the receivers operation. For an introduction

Two or three manufacturers offer PCI-style Satellite Receiver cards that fit inside a computer (regrettably only operating on MS Windows). Not only do these cards receive the programmes and store an unlimited amount of channel data, some versions of these cards can make the computer hard-disk operate as a personal digital video recorder (a 'PVR'). Also available are USB satellite Receivers for PC's and Mac's which connect to the computer with a USB cable .

To support the hobbist there are a few monthly magazines and several Internet Forums/newsgroups. By using appropriate search parameters on 'Google' (or other search engines) you will readily track these areas down.

 

Useful Links

Two of the most respected sources of up-to-the-minute listings of satellite transponders and programme providers are at:
www.lyngsat.com and www.satcodx.com

For the very best in technical info about digital and analogue satellite TV go to Martin Pickering's very own site:
www.satcure.co.uk

Visit The-Cool-Book-Shop.com and Your-Book store for e-Books about satellite TV and terrestrial digital TV.

For up-to-the-minute stuff about all aspects of Satellite TV visit the 'What Satellite Magazine' daily update pages at:
www.wotsat.com

For loads of up-to-date stuff about technical and political apects of UK satellite and terrestrial Digital TV visit:
www.dtg.org.uk

For info about installation of dishes (for Sky) and aerials (for Freeview) visit the Confederation of Aerial Industries Ltd:
www.cai.org.uk

For a very technical discussion of terrestrial and satellite DVB go here

For ex-pats who need info about receiving Astra-2D outside the normal footprint go here

For uncletony's page about UK analogue and digital television go here

Back to Home Page Rev: 03-2009