C-MAC
{{See also|CMAC (disambiguation)}}
Image:Multiplexed Analogue Components transmission (simulation).jpg
C-MAC/packet is a variant of the family of MAC (Multiplexed Analogue Components) systems for television broadcasting, developed by IBA and approved by the European Broadcasting Union (EBU) for satellite TV transmissions.{{Cite book |url=https://extranet.itu.int/brdocsearch/R-REC/R-REC-BO/R-REC-BO.650/R-REC-BO.650-2-199203-I/R-REC-BO.650-2-199203-I!!PDF-E.pdf#page=5 |title=RECOMMENDATION ITU-R BO.650-2 - Standards for conventional television systems for satellite broadcasting in the channels defined by Appendix 30 of the Radio Regulations |publisher=ITU |year=1992 |pages=5}}{{Cite journal |last=Buiting |first=J. |date=1990 |title=Introduction to Duobinary Encoding and Decoding |url=http://techdoc.kvindesland.no/radio/b2/20051213183809532.pdf |journal=Elektor Electronics |volume=January 1990 |pages=50–52}}
It was an analog television standard where luminance and chrominance components are transmitted separately in time rather than separately in frequency.{{Cite book |last=ITU Radiocommunication Assembly |url=https://extranet.itu.int/brdocsearch/R-REC/R-REC-BO/R-REC-BO.650/R-REC-BO.650-2-199203-I/R-REC-BO.650-2-199203-I!!PDF-E.pdf#page=18 |title=RECOMMENDATION ITU-R BO.650-2 - Standards for conventional television systems for satellite broadcasting in the channels defined by Appendix 30 of the Radio Regulations |year=1992 |pages=18}}{{Cite web |last=Government of Canada |first=Public Works and Government Services Canada |date=8 October 2009 |title=D2-MAC [1 record] - TERMIUM Plus® — Search - TERMIUM Plus® |url=https://www.btb.termiumplus.gc.ca/tpv2alpha/alpha-eng.html?lang=eng&i=1&index=ent&codom2nd_wet=1&srchtxt=D2-MAC |website=www.btb.termiumplus.gc.ca}} This was an evolution from older color TV systems (such as PAL or SECAM) where there was interference between chrominance and luminance.
Technical details
C-MAC required a bandwidth of about 22 MHz, making it unsuitable for direct-to-home or cable broadcast.{{Cite journal |last=Buiting |first=J. |date=1990 |title=Introduction to Duobinary Encoding and Decoding |url=http://techdoc.kvindesland.no/radio/b2/20051213183809532.pdf |journal=Elektor Electronics |volume=January 1990 |pages=50–52}}
The transmitter switches between FM (vision) and PSK (sound/data) modulation during each television line period. The digital information is modulated using 2-4PSK (phase-shift keying), a variation of quadrature PSK where only two of the phaser angles (±90°) are used, with a data rate of 20.25 Mbit/s.{{Cite book |url=https://extranet.itu.int/brdocsearch/R-REC/R-REC-BO/R-REC-BO.650/R-REC-BO.650-2-199203-I/R-REC-BO.650-2-199203-I!!PDF-E.pdf#page=5 |title=RECOMMENDATION ITU-R BO.650-2 - Standards for conventional television systems for satellite broadcasting in the channels defined by Appendix 30 of the Radio Regulations |publisher=ITU |year=1992 |pages=5}}{{cite web |last=Schlyter |first=Paul |title=MAC (Multiplexed analogue components) in "Analog TV Broadcast Systems" |url=http://www.stjarnhimlen.se/tv/tv.html#MAC}} This allows for the transmission of up to eight high quality (15 kHz bandwidth) sound channels.
C-MAC data was sent to the transmitter separately from the vision. The C-MAC standard included a standard scrambling system, EuroCrypt, a precursor to the standard DVB-CSA encryption system.
E-MAC
E-MAC (Extended MAC) is 16:9 version of C-MAC.{{Cite web |last=Pemberton |first=Alan |date=2024 |title=World Analogue Television Standards and Waveforms |url=https://www.bbceng.info/Technical%20Reviews/World-tv-standards/World%20Analogue%20Television%20Standards%20and%20Waveforms.html#MAC |access-date=2025-04-13 |website=BBCeng.info - Recollections of BBC engineering from 1922 to 1997}} Originally E-MAC was designed for 15:9 pictures, it later adopted the 16:9 aspect ratio.
- In E-MAC all the 4:3 information is transmitted exactly as in C-MAC so that C-MAC receivers are still compatible.
- E-MAC hides extra luminance and chrominance information in the field blanking interval and parts of the line blanking interval.
- E-MAC has a lower data capacity because luminance is hidden where data would usually be located.
- A 'steering' signal is transmitted to indicate to the 16:9 receiver whereabouts the 4:3 picture information.
- E-MAC receivers stitch the 4:3 and helper widescreen data into a seamless 16:9 picture.
See also
TV transmission systems