B-MAC

B-MAC^[1] is a form of analog video encoding, specifically a type of Multiplexed Analogue Components (MAC) encoding. MAC encoding was designed in the mid 80s for use with Direct Broadcast Satellite systems.^[2] Other analog video encoding systems include NTSC, PAL and SECAM. Unlike the Frequency-Division Multiplexing (FDM) method used in those, MAC encoding uses a Time-Division Multiplexing (TDM) method.

B-MAC was a proprietary MAC encoding used by Scientific-Atlanta for encrypting broadcast video services;^[2]^[3] the full name was "Multiple Analogue Component, Type B".

Usage

Both 625 and 525 line versions of B-MAC were developed and used.

This system was used in South Africa by Multichoice,^[4] and Australia by Optus^[2]^[5] (for TVRO until 2000).

B-MAC was used for satellite broadcasts of the American Forces Radio and Television Service from the early 1980s until 1996-1997 when the analogue standard was replaced by the digital PowerVu system.^[6]

B-MAC was used for direct to home satellite applications up to the mid-1990s when Primestar switched to an all-digital delivery system. It was also used in the US around the same time for C-band satellite feeds of live Pay-per-view events for reception by local cable TV operators to distribute to their subscribers, using equipment from Scientific-Atlanta.

Technical details

MAC transmits luminance and chrominance data separately in time rather than separately in frequency (as other analog television formats do, such as composite video). B-MAC uses teletext-style non-return-to-zero (NRZ) signaling with a capacity of 1.625 Mbit/s. The video and audio/data signals are therefore combined at baseband.

For audio, a format similar to NICAM was transmitted digitally rather than as an FM subcarrier.

The MAC standard included a standard scrambling system, EuroCrypt, a precursor to the standard DVB-CSA encryption system.

In MAC color is encoded using the YPbPr color space.^[7] Luma ( $Y'$ ) is derived from red, green, and blue ( $R',G',B'$ ) after gamma-correction (formula similar to PAL): $Y'=0.2997R'+0.587G'+0.1145B'$ ^[7]

Chrominance is computed based on $B-Y$ and $R-Y$ differences, generating two compressed and weighted color-difference signals, $P{\scriptstyle {\text{B}}}$ and $P{\scriptstyle {\text{R}}}$ .^[7]

The $Y'$ signal range is between -0.5 and 0.5 volts while $P{\scriptstyle {\text{B}}}$ and $P{\scriptstyle {\text{R}}}$ signals vary between -0.65 to 0.65 volts.

The following table lists the main technical parameters of B-MAC variants:^[7]^[8]

	B-MAC
Frame Frequency	29.97	25
Lines per frame	525	625
Aspect Ratio	4:3 / 16:9
Display Gamma	2.2	2.8
Primary chromaticities (x y)	Similar to NTSC 1953: Red 0.67, 0.33; Green 0.21, 0.71; Blue 0.14, 0.08
White point (x y)	D65
Luminance	$Y'=0.2997R'+0.587G'+0.1145B'$
Colour difference	$I'=-0.27(B'-Y')+0.74(R'-Y')$ $Q'=-0.41(B'-Y')+0.48(R'-Y')$	$R'-Y'=0.701R'-0.587G'-0.114B'$ $B'-Y'=-0.299R'-0.587G'-0.886B'$
Transmitted chrominance	$P'{\scriptstyle {\text{B}}}=0.694(B'-Y')$ $P'{\scriptstyle {\text{R}}}=0.926(R'-Y')$
Sampling frequency (MHz)	14.318	14.219
Uncompressed bandwidth (MHz)	4.2	5.0
Luminance clock periods	750
Chrominance clock periods	375

References

↑ Report 1074-1 - Satellite transmission of multiplexed analogue component (MAC) vision signals (PDF). ITU. 1990. p. 48.
1 2 3 Sandham, J K (November 1985). "To B-Mac or Not to B Mac (That is the Question)". Media Information Australia. 38 (1): 36. doi:10.1177/1329878X8503800 (inactive 9 October 2026).{{cite journal}}: CS1 maint: DOI inactive as of October 2026 (link)
↑ "Scientific Atlanta B-Mac satellite decoder, Series E9700, c 1995". Science Museum Group.
↑ Conradie, D.G. (19 June 1988). "The SABC's TV/radio satellite distribution system". COMSIG 88@m_Southern African Conference on Communications and Signal Processing. Proceedings. pp. 51–55. doi:10.1109/COMSIG.1988.49301. ISBN 0-87942-709-4. S2CID 131163463 – via IEEE Xplore.
↑ "8.3 Multiplexed Analogue Components Transmissions". happy.emu.id.au.
↑ "Scientific-Atlanta's PowerVu Technology Helping AFRTS Expand the Delivery of A Touch of Home to Military Abroad" (Press release). Atlanta, GA: Scientific Atlanta. PR Newswire. Retrieved 2014-05-29.
1 2 3 4 Slater, Jim (1991). Modern Television Systems to HDTV and beyond (PDF). pp. 62–65. ISBN 0-203-26370-7.
↑ 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 (PDF). ITU. 1992. p. 10.

External links

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

[1] Report 1074-1 - Satellite transmission of multiplexed analogue component (MAC) vision signals (PDF). ITU. 1990. p. 48.

[:2-2] 1 2 3 Sandham, J K (November 1985). "To B-Mac or Not to B Mac (That is the Question)". Media Information Australia. 38 (1): 36. doi:10.1177/1329878X8503800 (inactive 9 October 2026).{{cite journal}}: CS1 maint: DOI inactive as of October 2026 (link)

[3] "Scientific Atlanta B-Mac satellite decoder, Series E9700, c 1995". Science Museum Group.

[4] Conradie, D.G. (19 June 1988). "The SABC's TV/radio satellite distribution system". COMSIG 88@m_Southern African Conference on Communications and Signal Processing. Proceedings. pp. 51–55. doi:10.1109/COMSIG.1988.49301. ISBN 0-87942-709-4. S2CID 131163463 – via IEEE Xplore.

[5] "8.3 Multiplexed Analogue Components Transmissions". happy.emu.id.au.

[6] "Scientific-Atlanta's PowerVu Technology Helping AFRTS Expand the Delivery of A Touch of Home to Military Abroad" (Press release). Atlanta, GA: Scientific Atlanta. PR Newswire. Retrieved 2014-05-29.

[:1-7] 1 2 3 4 Slater, Jim (1991). Modern Television Systems to HDTV and beyond (PDF). pp. 62–65. ISBN 0-203-26370-7.

[8] 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 (PDF). ITU. 1992. p. 10.

[avs-9] 1 2 Also used in China's DVB-S/S2 network.

[mobaho-10] 1 2 Defunct.

[1]

[2]

[3]

[4]

[5]

[6]

[7]

[8]

[note 1]

[note 2]

v t e Analog television broadcasting topics
Systems	180-line 343-line 375-line 405-line (System A) 441-line 455-line 525-line (System M) 625-line (System B, System C, System D, System G, System H, System I, System K, System L, System N) 819-line (System E, System F)
Color systems	NTSC NTSC-J Clear-Vision PAL PAL-M PAL-S PALplus SECAM
Video	Back porch and front porch Black level Blanking level Chrominance Chrominance subcarrier Color burst Color frame sequence Color killer Color TV Composite video Frame (video) Horizontal scan rate Horizontal blanking interval Luma Nominal analogue blanking Overscan Raster scan Safe area Teletext Television lines Vertical blanking interval Vertical interval timecode White clipper
Sound	Multichannel Television Sound NICAM Sound-in-Syncs Zweikanalton
Modulation	Frequency modulation Quadrature amplitude modulation Vestigial sideband modulation (VSB)
Transmission	Amplifiers Antenna (radio) Broadcast transmitter/Transmitter station Cavity amplifier Differential gain Differential phase Diplexer Dipole antenna Dummy load Frequency mixer Intercarrier method Intermediate frequency Output power of an analog TV transmitter Pre-emphasis Residual carrier Split sound system Superheterodyne transmitter Synchronization of TV transmitter and receiver Television receive-only Direct-broadcast satellite television Television transmitter Terrestrial television Transposer Digital television transition
Frequencies & bands	Frequency offset Microwave transmission Television channel frequencies UHF VHF
Propagation	Beam tilt Distortion Earth bulge Field strength in free space Noise (electronics) Null fill Path loss Radiation pattern Skew Television interference
Testing	Distortionmeter Field strength meter Vectorscope VIT signals Zero reference pulse
Artifacts	Dot crawl Ghosting Hanover bars Sparklies

Usage

Technical details

See also

References

External links