Rough guide to BMAC

[nanochickin]

B-MAC

Scientific-Atlanta's B-MAC (Multiple Analogue Component, Type B) scrambling system was used by numerous satellite programmers and service providers. Within the Asia-Pacific region, users of B-MAC included HACBSS and RCTS service providers in Australia, the Indovision DTH program package on Palapa C2 (HBO, ESPN, Discovery Channel, and TNT/Cartoon Network) various program providers using the Apstar 1 satellite (Discovery Channel, Disney Channel, ESPN, and HBO) Channel 9 Australia and Hong Kong/Macao horseracing service providers.

B-MAC encryption offered hard video security through a technique known as line translation scrambling. Each line of video information is delayed by several microseconds, creating B-MAC's characteristic diamond-hatched pattern. Only those terminals equipped with decoders that are addressed by a packet of data contained in the vertical blanking interval of the B-MAC signal can descramble the signal. B-MAC's horizontal blanking interval contains up to six digitally-encrypted audio channels and one utility data channel.

While B-MAC did supply customers with relatively-secure and addressable communications signals, it was not just another scrambling system. B-MAC provided the additional benefit of increased signal performance at low carrier-to-noise levels when compared to an NTSC video transmission. B-MAC's improvements over NTSC equated to savings for past users, since they could use smaller, less expensive ground stations on the receive portion of the network. B-MAC sequentially transmitted the color information in one-third the active scanning time of each frame and the monochrome information in two-thirds the active scanning time. This prevents the chrominance and luminance signals from interacting with each other, thereby generating unwanted artifacts in the video. The video performance was further improved by the use of a digital sync pulse.

See first picture. color information on left of pic, monochrome information on right of pic.

By displaying the video's vertical blanking interval, the individual lines which carry various signals could be displayed. Line one transported the digital clock recovery signal, line two carried the digital sync recovery signal, line three sent the system data, lines four through nine handled the address data packets and lines 10 through 15 held teletext packets. The horizontal blanking interval could contain as many as six 204 kb/s digital audio channels and one 63 kb/s utility data channel.



Display of B-MAC Vertical Blanking Internal (2nd Picture)

The digital encryption standard key to the line delay pattern for any service can be changed at frequent intervals, precluding a one-time cracking of the code. Only those terminals equipped with B-MAC decoders which are addressed via a packet of data contained in the vertical blanking interval can switch on and decode the signal.

Taken from the Satellite TVRO Handbook

[satsid]

hi nano on above,these things you use to be able to get by x_army stuff.the x army things are supose to be great for many things in satellite.some of this years back i tryed to get hold of,but somone beat me to it.that was the 1 & only time i heard of anyone selling.this guy had b mac & all sorts of things for dish,& even dishes that was x army.to this day i wish i had got my hands on them.never mind we cant win them all.
sid

[Likvid]

I had AFN in 1988 receiving it on Intelsat 1 West in C-band with my Winegard 3.1m dish.

They transmitted on the weak global beam with EIRP down to 32dBW in my area.

I think i paid about £1200 in your currency for the B-Mac decoder.

[Kay B]

@ Likvid

Cool, AFRTS via B-MAC. Do you still have recordings of AFRTS? I am looking for the 80s style AFRTS jingle (stars with the earth coming from one and the AFRTS logo from the other side) in full NTSC resolution (480 lines @ 29.97 fps).

[Likvid]

Sorry no, i don't have any recording from back then left, i had a Sony Betamax which i recorded everything with and sadly my mom threw it all away when we moved as our Betamax was broken and old.

My reception was nearly at threshold level with loads of sparklies because it was transmitted on the weak global beam.

[Likvid]

Here is a picture i found, it was loads of sparklies as the picture below.

Good old days, here is a video from it http://www.maetzi.info/images/Videos/AFRTS.avi

[Kay B]

@ Likvid

Do you have any pictures of you B-MAC decoder?

[Likvid]

No i sold it for £1200 back in 1993