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{{One source|date=June 2024}}{{short description|Signal transmitted for test purposes in TV transmitters}}
'''Zero reference pulse''' or '''Zero pulse''' is an artificially produced pulse in a professional television receiver imitating no [[radio frequency]] case for [[modulation]] index measurements in analogue [[TV transmitter]]s.
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==Measurement==
[[File:0 pulse.svg|thumb|
To adjust the modulation index, an input of maximum level CVS (1000 mV) is applied to the modulator. The modulated RF signal is then applied to a professional TV receiver . The receiver has a facility to switch off RF for a short interval in each consecutive line. So during this interval, modulation ratio is effectively 0%. The interruption on all lines in a frame is observed as a vertical white bar on a visual monitor. This bar is named as 0 reference pulse (or simply 0 pulse).
The oscillogram of the 0 pulse is a pulse with a level more than the maximum level of the CVS. Taking the level difference between the [[Analogue television synchronization|sync]] tip and the 0 pulse as % 100, the maximum CVS should be 10% or 12.5%. The adjustment of the modulation index is simply the level adjustment of the modulating signal (CVS) at the input of the modulator.
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