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Color Television
Luminance -vs.- Chroma Delay
Simple unibar generator of special design
provides at the encoder output a signal whose
waveform pattern can be examined for
symmetry as an accurate qualitative check
of delay
Fig. 9: I
delay .02 u.s shorter than Y
Fig. 7: Y delay .05 .,.s longer than Q
Fig. 8: Encoder output, Y and I. Balanced
Fig. 10: I
delay .05 u.s shorter than Y
quires a delay check whenever
adjustments are made affecting 1
and Q band -pass. In broadcast
installations where compliance
with FCC specifications must be
maintained, it is likewise essential
that routine performance
measurements include a check of
luminance -vs- chrominance delay.
As a matter of fact, this measurement
can be used for a more sensitive
indication of drift in band -
pass characteristics than is afforded
by the more direct method
of measuring amplitude - vs - frequency
response.
The technique herein described
was developed primarily to facilitate
routine operational maintenance
of broadcast encoding
equipment, but is readily applica-
ble to the reverse situation encountered
in the decoding section
of receivers or picture monitors.
Direct Measurement
Although not specifically so
stated in the FCC specifications,
the ±0.05 µsec relative timing tolerance
is interpreted as applying
to a point of reference corresponding
to the voltage midpoint of a
step function in each signal component.
The simplest approach
for direct measurement is to compare
the position of these points
on a triggered oscilloscope, observing
separately each signal
component while the encoder
(RGB) input consists of time -coincident
pulse signals proper -
(Continued on. page 187)
Fig. 11: 1 delay .02 u.s longer than Y
Fig. 12: I delay .05 p.s longer than Y
Tele -Tech & ELECTRONIC INDUSTRIES
June 1956
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