Notice the top line is Peak-of-Sync and two centimeters down from the top line is Blanking. Also,
one centimeter up from the bottom line is “White”. These three points will be referred to later in this
procedure.
To obtain this pattern it is necessary to first setup the Pac-Mono equipment per their procedure.
Connect the “five step” video from the signal generator to the
input
of the Pac-mono card. The
output of the Pac-Mono equipment is then connected to the
video input
of the ADC transmitter.
Verify the transmitter is in the
Auto-Clamp
mode by moving the
Manual/Auto Clamp
switch
found on the
Modulator Module
to the right. The scrambling equipment should be in the Normal
or Unscrambled mode.
With the transmitter in Operate, adjust the Depth of Modulation
slightly
using the
Video Gain
control on the Modulator Module until the waveform looks similar to Fig. 1.
Note
: Verify the Spectrum Analyzer has a Bandwidth setting of 1MHz to minimize the effects of any
adjacent channels.
Verify the Manual Clamp mode is set correctly by moving the
Manual/Auto Clamp
switch found on
the
Modulator Module
to the left and adjust the Manual Bias until the pattern is similar to Fig. 1.
Leave the
Manual/Auto Clamp
switch in the
Manual Mode
.
This completes the pre-adjustment of the transmitter with scrambling off.
Place the Pac-mono equipment into the
Scrambled Video Mode
. This will remove the Peak-of-
Sync. line and move Blanking upward towards the top of the screen.
Locate the
Gate Level
adjustment control on the front of the Power Amplifier Module. Adjust the
control
slightly
until the Blanking level moves back to its original position, two centimeters down
from the top of the screen.
Change the signal on the video generator to
Zero IRE, No Burst
. This will reveal a line 3 centime-
ters down from Blanking. This is the Sync line in Scrambled Mode. Verify this line is 3 centimeters
down. If not, adjust the manual clamp
slightly
to correct the offset.
Disconnect the Signal Generator and connect Live Video. While viewing the Live Video on the Spec-
trum Analyzer, verify the white levels are one centimeter up from the bottom of the screen. If they
are not, adjust the video coming from the IRD or other video source.
Do not readjust the trans-
mitter video gain. This will change the scrambled Sync level and cause picture problems.
This completes the transmitter setup.
NOTE
:Peak/Avg fault should be dissabled any time you are transmitting analog signals.....Enabled
when transmitting digital (QAM)
Video present fault should be enabled only when there is NEVER going to be video encoding that
envolves the removal of horiz and/or vertical sync at the baseband level. i.e. Any system that
requires the clamp to be in manual mode should have the video present fault dissabled. This in-
cludes Pac mono and Cal Amp. By the way, the video fault sensing circuitry only works reliably in
the clamp on mode.
17
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