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Question on Multiplex & Demulitplex a Video signal

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muaythai2006

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NTSC video has bandwidth 4.2 MHz,30 frames/s,525lines/frame,interlace. The total bandwidth of TV chanel is 6 MHz(Video +Audio).Video signal has Luminace+chrominance signals. Chrominance has I and Q components.

My question is how can u find fc(color subcarrier) for chominace.Example from my class note fc=30*240/2*225=0.81MHz . I don't know what those values are coming from. Also the low pass filter in QMA modulator f_LPF1= 30*240/2*150=0.54MHz (5.4E5) and low pass filter f_LPF2=0.2MHz (2E5)) in QMA demodulator.
 

fc is 3.579545+ MHz. It's derived from the 4.5 MHz sound carrier to avoid audio from causing visible flicker:
fc = 4.5 MHz * 35 / 44.

I don't recall how the modulation bandwidths were derived.
 

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