Quote:
Originally Posted by old_tv_nut
You need to learn the difference between an electrical signal vs time and its spectrum of frequencies.
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I know. This is what I am asking help with
If you can point to the graph and say "this is this" and "this is that", I will be grateful.
Quote:
Originally Posted by old_tv_nut
The diagrams you posted are frequency spectra, and represent a long term average of the different frequencies in the signals. In general, a lower frequency (towards the left) represents a coarse repeating pattern of lines or dots in the picture, and higher frequencies represent finer patterns. When such a signal is modulated on a carrier, it generates new frequencies spaced up and down from the carrier frequency.
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The diagrams I posted are different one from another.
- The TV broadcast spectrum is U(f), where U is strength at a particular f, so I suppose the whole band can describe level for, say, 6 million samples, which is a whole frame for, say, 1/30 of a second. Then the next 1/30 of a second I would have a different snapshot of a 6 MHz bandwidth, do I get it right?
- On a VTR, brightness is coded as frequency, not amplitude, I get it. But I thought that brightness is confined between the tip of the carrier and its deviation. So, say brightness is between 3.5 and 4.5 MHz. If this is correct, what is to the left of the tip?
Quote:
Originally Posted by old_tv_nut
The FM modulation of the luminance in video tape is called "narrow band" because the FM deviaton is in the same order as the bandwidth of the video baseband. Compare this to FM radio, where the deviation is larger than the baseband audio frequencies.
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So what the deviation is for, and what the baseband is for? Is baseband to the left of the tip point, or all luminance including the deviation?
Quote:
Originally Posted by old_tv_nut
The overall bandwith of the video tape FM luminance is a combination of the baseband signal bandwidth and the deviation. If the carrier is too low in frequency the combination can suffer distortion.
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How is that? Although I think I've read somewhere about why the carrier was chosen as high as possible, need to re-read.