[ToC]

 

VECTORGRAM INDICATES THAT THE B—Y SIGNAL HAS MUCH MORE BASELINE CURVATURE THAN THE R—Y SIGNAL

Robert G. Middleton, Using Scopes in Color TV, Howard W. Sams & The Bobbs-Merrill Companies, NY, 1969

Fig 7-13 [right] shows the appearance of a vectorgram in which the B—Y signal has much more baseline curvature than the R—Y signal. In this example, the inner ellipse is so narrow that it is almost a straight line. Note that the inner excursion of a vectogram will be a straight horizontal line segment in case that the R—Y waveform has no baseline curvature, while the B—Y waveform has a curved baseline. The basic principles that are involved are as follows:

1. In an ideal vectorgram, the petals come to a point in the center of the pattern.

2. The central portion of a vectorgram is a circle, ellipse, or occasionally a straight-line segment in practical situations.

3. Inner circles or ellipses result from baseline curvature in the R—Y and B—Y waveforms.

4. Baseline curvature is caused by subnormal bandwidth in a chroma channel, or by a defective diode in a chroma demodulator.

5. Subnormal bandwidth can be caused by an open high-frequency compensating capacitor, or by misalignment of the chroma circuits.