What is the need of MAC encoding? Explain the general format of MAC signal for transmitting colour TV signals.

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written 6.7 years ago by

teamques10 ★ 68k

MAC stands for Multiplexed Analog Component signal, it uses interlaced scanning and the luminance and chrominance information for each line is being scanned and is transmitted simultaneously but in the interleaved form.
A separate additional carrier is being transmitted for a monophonic sound and two additional sound Carriers are transmitted for the stereophonic sound.
All these careers will interfere each other and cross luminance and cross colour effect that are associated with the areas of high colour saturation are observed.
Mac system allows to introduce feature like digital video effect because it maintains the video component separate by compressing the luminance and chrominance signals and then placing the signals on the same line along with the digitized sound as well as sync signal.
MAC system the luminance and chrominance signals are multiplexed using TDM technique and they are separated in time domain and send as separate components this will eliminate the interference.
MAC system uses frequency modulation with upper channel bandwidth of 24 MHz and operates in 12 GHz frequency band.
The scanning period of one horizontal line is 64 µsec and the colour and brightness signals are transmitted sequential using TDM

MAC Encoding Signal

According to the digital component studio standard the scanning frequencies for luminance and chrominance signals are 13.5 MHz and 6.75 MHz respectively.
These frequencies suggest that compression factor for Luminance signal is 1.5 where is compression factor for chrominance signal is 3.
Chroma signals are time compressed by a factor of 3, it means their sampling rate in 6.78 MHz, they are written at 20.25 MHz, which is 3 times higher.
After this Chroma signals are multiplexed in a sequential manner does during the forward scanning time of 64 µsec, signal U and V alternately occupy the 17 µsec slot, followed by Luminous signal occupy 35 µsec.
The U signal is transmitted during the odd lines and the Y signal is transmitted during the even lines of the picture.
The drawback of this process is that the useful vertical resolution will be limited to a smaller value.

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