D-MAC - AbsoluteAstronomy.com

Among the family of MAC or Multiplexed Analog Components systems for television broadcasting, D-MAC is a reduced bandwidth variant designed for transmission down cable.

The data is duo-binary coded
Bipolar encoding
In telecommunication, bipolar encoding is a type of line code . A duobinary signal is such an encoding.- Advantages :...

with a data burst rate of 20.25Mbit/s so that 0° as well as ±90° phasors are used.
D-MAC has a bandwidth of 8.4 MHz versus 27 MHz for C-MAC
C-MAC
C-MAC is the variant approved by the European Broadcasting Union for satellite transmissions. The digital information is modulated using 2-4PSK , a variation of quadrature PSK where only two of the phaser angles are used....

.
Most cable systems work on EBU 7 MHz channel spacing, so this approach did not work universally.
D-MAC's bandwidth problems were later fixed by D2-MAC.

D2-MAC: A fix for D-MAC

D-MAC consumed too much bandwidth for many applications, so D2-MAC was designed for European cable TV systems.

Luminance and chrominance

MAC transmits luminance and chrominance data separately in time rather than separately in frequency (as other analog television formats do, such as composite video).

Audio and scrambling (selective access)

Audio, in a format similar to NICAM
NICAM
Near Instantaneous Companded Audio Multiplex is an early form of lossy compression for digital audio. It was originally developed in the early 1970s for point-to-point links within broadcasting networks...

was transmitted digitally rather than as an FM subcarrier.
The MAC standard included a standard scrambling system, EuroCrypt
EuroCrypt
EuroCrypt is a conditional access system for Multiplexed Analogue Components-encoded analogue satellite television. It had several versions . It supported receivers with card slots and those with embedded keys...

, a precursor to the standard DVB-CSA encryption system.

History and Politics

MAC was developed by the UK's Independent Broadcasting Authority

Independent Broadcasting Authority

The Independent Broadcasting Authority was the regulatory body in the United Kingdom for commercial television - and commercial/independent radio broadcasts...

(IBA) and in 1982 was adopted as the transmission format for the UK's forthcoming direct broadcast satellite

Direct broadcast satellite

Direct broadcast satellite is a term used to refer to satellite television broadcasts intended for home reception.A designation broader than DBS would be direct-to-home signals, or DTH. This has initially distinguished the transmissions directly intended for home viewers from cable television...

(DBS) television services (evntually provided by British Satellite Broadcasting

British Satellite Broadcasting

British Satellite Broadcasting was a British television company which provided direct broadcast satellite television services to the United Kingdom...

). The following year MAC was adopted by the European Broadcasting Union

European Broadcasting Union

The European Broadcasting Union is a confederation of 74 broadcasting organisations from 56 countries, and 49 associate broadcasters from a further 25...

(EBU) as the standard for all DBS.

By 1986, despite there being two standards, D-MAC and D2-MAC, favoured by different countries in Europe, an EU Directive imposed MAC on the national DBS broadcasters, to provide a stepping stone from analogue PAL

PAL

PAL, short for Phase Alternating Line, is an analogue television colour encoding system used in broadcast television systems in many countries. Other common analogue television systems are NTSC and SECAM. This page primarily discusses the PAL colour encoding system...

and Secam

SECAM

SECAM, also written SÉCAM , is an analog color television system first used in France....

formats to the eventual high definition

High-definition television

High-definition television is video that has resolution substantially higher than that of traditional television systems . HDTV has one or two million pixels per frame, roughly five times that of SD...

and digital television of the future, with European TV manufacturers in a privileged position to provide the equipment required.

However, the Astra

SES Astra

Astra is the name for the geostationary communication satellites, both individually and as a group, which are owned and operated by SES S.A., a global satellite operator based in Betzdorf, in eastern Luxembourg. The name is sometimes also used to describe the channels broadcasting from these...

satellite system was also starting up at this time (the first satellite, Astra 1A

Astra 1A

Astra 1A was the first satellite launched and operated by SES . During its early days, it was often referred to as the Astra Satellite, as SES only operated one satellite originally....

was launched in 1989) and that operated outside of the EU’s MAC requirements. Through the 1990s, a battle raged between the proponents of PAL on Astra and MAC on the DBS satellites. Despite further pressure from the EU (including a further Directive originally intended to make MAC provision compulsory in TV sets, and a subsidy to broadcasters to use the MAC format), the broadcasters and viewers preferred the ease and lower cost of PAL equipment and voted with their dishes, choosing the pan-European PAL broadcasts of Astra over the national DBS satellites.

By the mid-1990s, the unexpectedly rapid rise of digital broadcasting technology rendered the arguments irrelevant, and the use of D-MAC and D2-MAC faded away.

External links

Multiplexed Analogue Components in "Analog TV Broadcast Systems" by Paul Schlyter

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.

D2-MAC: A fix for D-MAC

Luminance and chrominance

Audio and scrambling (selective access)

History and Politics

See also

External links