The Use of Echo Time-Weighting to Derive Oscilloscope Graticules for Rating Television Transmission Performance

Gain and phase deviations in the transmission path of a television signal above 300 kHz affect the smallest picture elements of the signal and may cause undesirable echoes and loss of resolution in the picture. This type of “short-time” distortion may be evaluated by waveform measurements using a test signal and an oscilloscope graticule. The test signal selected is the standard “sine-squared” step. The graticule design assumes transmission impairment to be subjectively equivalent to that of a single well-displaced echo of appropriate magnitude. Thus, the envelope of the sum of the test signal and its delayed echo define the graticule contours. The relative amplitude of the delayed echo is determined from the results of subjective single-echo time-weighting tests. The derivation of this envelope, while approximate, takes into account the rise time of the test signal and the normalization process that enters into adjusting the oscilloscope. The graticule as it is used applies directly to transmission impairments that give rise to single-echo distortion. Experience in using similarly derived graticules for visual-telephone testing indicates the method to be useful for multiple and smeared echo distortions.

Print ISSN

0036-1682

Published

1976-06

Content type

Original Research

DOI

10.5594/J06821