Quote:
Originally Posted by Pete Deksnis
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The really interesting question becomes: is there really any significant cross-color resuling from demodulation in the 21-CT-55 versus the CTC2?
I suspect very little.
Pete
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Actually, moving the I axis to R-Y would produce no crosstalk. The Q signal is narrow band, and the I signal has both low frequency sidebands (double) and high frequency (lower sideband only).
Since the wideband R-Y demodulator is properly matrixed to form the R signal when combined with the Y signal, it gets the correct proportions of I and Q low frequencies (in the double sideband region below +/- 500 kHz).
What does the R-Y demodulator get in the high-frequency I region? Because it is not exactly in phase with the I signal, it gets mostly the correct I high frequencies; but it also gets a small proportion of the Hilbert transform of the I high frequencies (that is, I high frequencies with a 90 degree phase shift). The result is that the R-Y shows some distortion of high frequency transients that would be perfect in a true I demodulator.
sin (33) = .545 (pretty large) - multiplier for the undesired Hilbert component.
cos (33) = .839 - multiplier for the desired I signal, which also is the correct multiplier for the I component of R-Y.
Wikipedia has an illustration of a square wave and its Hilbert transform:
http://en.wikipedia.org/wiki/Hilbert_transform
If the original I signal is a square wave of frequency greater than 500 kHz , what comes out of the R-Y demodulator is a sum of the square wave and a smaller proportion of the shown Hilbert transform. So, rising edges get pushed towards cyan, and falling edges get pushed towards red.
Whether this is noticeable or not will depend on the subject matter and also on whether the viewer knows what to expect. In most cases, these kinds of distortions do not become strongly apparent unless you have a correct picture to compare to. There might be exceptions for things like colored title letters, which the viewer may assume to originally have uniform color on the left and right edges.