AC - alternating current
ACTS - Advanced Comminication Technologys and Services. A European Commission research and development funding programme including digital broadcasting and next-generation Internet. Projects were as follows: Motivate: Mobile Digital Terrestrial Television. Crabs / Cabsinet: next generation LMDS for broadband local loop connection at 40GHz iTTi: Return Channel for DVB-T. MoMuSys: mobile multimedia systems. Diceman: using new technologies to exploit AV archives. CustomTV: MPEG4/7 object based interactivity over MPEG2 transport streams. STORit: Use of local hard disc store to enhance functionality in home entertainment systems. Infobridge: Promotion and dissemination of information from the ACTS projects ACTS has now finished and future work in this area continues under the IST framework programmes.
ACTUATOR - A motor system to drive a motorised multi-satellite dish.
ADSL - Assymetric Digital Subscriber Line. Invented by US company Bellcore (now Telcordia Industries) in 1989. ADSL has greater bandwidth in the forward path than the return path. It uses existing copper twisted pair local loop. Its main advantage is the ability to roll out broadband to the home without digging up the pavement again. Crosstalk fundamentally limits the distance from the exchange it can work at a given bandwidth. 2Mb/sec is the calculated limit to reach 80% of existing connections. It is an essentially different way to provide broadband connection to the method employed in cable modems. Fundamentally it allows several users in the home to access the available bandwidth simultaneously whereas, with a cable modem, you need a second subscription for a second service. Likewise, this sharing of capacity is also an important feature to the telco operator which may become significant when local loop connections become extensively used for broadband applications. The ADSL Forum is the industry group which is working to further development. It is estimated that there are about 100,000 existing ADSL connections in the world at this time but with consumer chipsets now in volume production, this is expected to grow very steeply in the next few months and years.
AFD - Signal transmitted in UK DTT to ensure various types of letterbox picture are displayed to best effect on both 4x3 and 16x9 television sets.
AM - The Conditional Access Module provides the crucial conditional access technology required to decode the scrambles signals broadcast by the service provider.
AMPLIFIER - An electronic device used to increase the strength (power) of a signal fed into it.
ANALOGUE - Historical mode of transmission, uses standard wave to transmit television services.
ANAMORPHIC - 16x9 Anamorphic. Used to differentiate a 16x9 widescreen picture which fills the whole frame, from a 16x9 letterbox with blank lines at the top and bottom of the frame. The Americans don't understand anamorphic in the context of television. Their equivalent term is 16x9 full frame.
ANTENNA - A device for transmitting or receiving radio waves. Also known as aerial. In satellite communication systems the antenna usually consists of a parabolic reflector and a feedhorn. In a receiving system the reflector focuses radio waves onto the feedhorn for detection and conversion into electrical signals. In a transmitting systems the reflector concentrates the radio waves emitted by the feedhorn into a narrow beam aimed towards the satellite.
API - The Application Programme Interface is the operating system which provides the EPG and interactive functions in the digital receiver. It is the equivalent of Windows in a PC. Existing proprietary APIs such as MediaHighway and OpenTV have fought a battle for the same dominance that Windows achieved but the tide has turned in favour of an open standards API. Many people believe that should be MHEG-5 and Canal+, the owners of MediaHighway, have committed to changing over to it. But MHEG-5 is an anathema to the Americans. The common denominator for the future is Java and this has now been adopted by the DVB Project for their Multimedia Home Platform development. MHEG-5 and other existing systems will become plug-in classes to a Java Virtual Machine.
ASA - Authorised Sky Agent
ASHA - Authorised Sky Homes Agent
ASTRA - The main satellites for UK and European reception. Astra lA-lK orbit the Earth at 19.2 degrees East, and supply hundreds foreign digital channels. Astra 2A-2D orbit at 28.2 degress East providing Sky Digital signals.
ATM - ATM stands for Asynchronous Transfer Mode and is a method that is taking the telecom industry by storm for splitting digital audio, video or data signals into little data packets, which can all be fed together into ginormous bitstreams and, with luck, reach their right addresses and can be put back together in the right order.
ATT - Analogue Terrestrial Television. Conventional television, limited to just 4 or 5 channels.
ATTENUATOR - A passive device that weakens a signal that passes through it. The amount by which the signal power is reduced is usually expressed in decibels.
AUDIO DESCRIPTIVE BROADCASTER - Services that carry an additional audio stream describing The people who broadcast TV programmes
AV - (Audio Visual) A Blanket term for audio and video. An AV system is a common description of a setup in which a TV and hi-fi are connected, working together as "home cinema".
AZIMITH - The horizontal angle between an antenna's reception path and a compass direction. Usually expressed as a compass bearing or degrees East or West of South.