Joe Nicholson wrote in a message to Tom Walker:

 JN> The standard for the two color signals is 1.5MHz for the I signal 
 JN> and 0.5 MHz for the Q signal.  TV sets up to about 1964 
 JN> demodulated on those two 90ø signals.  The I and Q signals then 
 JN> underwent further processing to come up with R-Y, B-Y and G-Y 
 JN> signal for the pic tube.

I haven't thought about this stuff in *ages*.  Remembering trying to
comprehend it in books about how it worked,  that stuff made my head hurt! 
:-)

 JN> Eventually manufacturers learned to demodulate on the R-Y axis and 
 JN> the B-Y axis (both 0.5 MHz) and combine them in such a fashion to 
 JN> get a G-Y signal.

 JN> Note that now the viewer has 1 MHz less color signal or 
 JN> information (quality, if you want to call it that).

I don't think I'd call it that.  

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