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Old 12th Dec 2022, 5:18 am   #13
Synchrodyne
Nonode
 
Join Date: Jan 2009
Location: Papamoa Beach, Bay of Plenty, New Zealand
Posts: 2,852
Default Re: Group delay (in analogue modulation / transmission systems)

Some transmission authorities included group delay pre-correction (pre-distortion) in their analogue TV transmitter specifications in order to counter the expected group delay distortion in typical domestic receivers. I think that originally, it was done at low-to-mid video frequencies for monochrome reception, with correction at higher video frequencies (around the colour subcarrier) in the colour era.

Commentary on the matter showed up in the CCIR/ITU-R TV System reports from 1974 Geneva onwards. I have attached a couple of examples group delay curves are shown towards the end. (The whole set may be found at the ITU site.)

CCIR 1974 Geneva Report 624 TV Systems.pdf ITU-R BT.1701-1 200508 TV Systems.pdf

Evidently post-demodulation video group delay correction was sometimes included in higher performance receiving systems. I have attached a couple of examples, one with L-C and the other with SAW vision IF filtering.

BBC RC1-511 Block Schematic.pdf WW TV Tuner Block & Vision Schematics.pdf


Cheers,
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