Explain D2-MAC packet format signal and state characteristics of D2-MAC

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written 6.7 years ago by

teamques10 ★ 68k

• modified 5.3 years ago

In order to transmit the sound signal digitally, the C-MAC system which uses the BPSK or QPSK modulation was initially considered.
But later on this idea was discarded because it requires a very large bandwidth of 12 MHz, instead of D2-MAC system which uses the duo-binary coding for sound was selected.
The duo-binary coding is useful for reducing the bandwidth required for the digital sound.
In D2-MAC system for the transmission luminance and colour difference signal TDM is used, the signals are not sent simultaneously but they are sent sequential one after another.

D2-MAC Packet enter image description here

In D2-MAC, the analog video and digital sound are multiplexed before modulation. The modulation of subcarrier will take place after that.
It is possible to use AM/VSB for cable TV and FM for satellite broadcasting.
The duo-binary uses three levels of signals instead of two and reduces the bandwidth requirement by 50%.

Characteristics of D2-MAC:

1.	Lines per image	625
2.	Lines with data burst	1 to 625
3.	Lines with video signal	24 to 310 and 336 to 622
4.	Lines with luminance signal	Y in every line
5.	Lines with chrominance signal	U on odd lines, Von the even lines
6.	Ratio of interlace	2 : 1
7.	Aspect ratio	4 : 3/(5.33 : 3)
8.	Ratio of luma compression	3 : 2
9.	Ratio of Chroma compression	3 : 1
10.	Sampling frequency	20-25 MHz
11.	Instantaneous bit rate	10.125 Mbps
12.	Samples per line	1296
13.	Samples for luminance	349
14.	Samples for luminance	697
15.	Bits per data burst	105(6 bits H sync. + 99 data bits)

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