Operation
PULSAR
Page 5-10
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CLAMPING
The video clamper is used to hold the blanking level constant, regardless of the changes in the average
picture level. Two different methods of clamping are selectable: back porch or sync tip clamping. Back
porch clamping is used in most cases and is based upon the sample & hold principle. It is especially
used when hum rejection is wanted. If the video signal becomes too noisy or when specific types of
scrambled video signals are used, back porch clamping is no longer possible. The solution is the sync tip
(peak) clamping method which is based on a simple peak detection system which is a slow system. Use
sync tip clamping in case of a too noisy video signal or some specific types of scrambled video signals.
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VAGC
The video AGC can be white referred or sync referred. The selectable AGC mode depends upon the
clamping mode:
CLAMPING = B-PORCH:
video AGC: OFF
video AGC: WHITE (white referred)
video AGC: SYNC (sync referred)
CLAMPING = SYNC:
video AGC: OFF
video AGC: SYNC
White referred video AGC can only be selected in case back porch
clamping is used. The white level meter will only work if VITS lines with
white level are included in the video signal. White referred video AGC is
not possible without these lines.
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MOD-METER:
The modulation meter detector follows the AGC when switched to sync or white. The modulation meter
can never be put on white if sync clamping is used.
5.4.9 White Limiter
The white limiter circuit is used to avoid overmodulation. Overmodulation could cause audio buzz in
home receivers. Press the
UP
and
DOWN
arrow to toggle between on or off.
5.4.10 Audio Preemphasis
The audio preemphasis can be activated or disactivated using this menu.
The unit is only prepared for IRT stereo. There is no standard stereo encoder inside the modulator.
REMARK
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