Axcera CHV400BTD, Technical Manual, Page: 72 / 87

Innovator CHV400BTD ATSC Transmitter System Set Up Procedure
Technical Manual, Rev. 0 68
Figure 16A: (A5) ALC Board (1308570)
Refer to Figure 16A. Turn the output power down to 10% power with R62 on the
ALC Board. Remove the output RF connector from J2 on tray and calibrate the
reflected power to 10%, using R7, the Reflected Calibration pot, on the Output
Detector Board. Refer to Figure 17. Re-connect the RF output connector to the tray
and increase the power, in Manual gain using R62 on the ALC Board, to 115%.
Adjust the Overdrive pot R38 on the ALC Board, CCW until the overdrive threshold
just trips and the Overdrive Fault LED DS4 lights. Turn R38 slightly CW so that
power comes back up and DS4 goes out.
Switch S1 on the ALC Board to ALC. Turn the ALC Adjust pot R75 on the ALC Board
until the power is 100%. Switch S1 between ALC and Manual to verify smooth
switching, with minimal change in power. If necessary repeat the above procedure.
With the tray in ALC, use the ALC Adjust pot, R75, to decrease the power to 10%.
Remove the RF output connector from the tray. Verify that the VSWR Cutback LED,
DS6, comes on and the Reflected Power drops to approximately 6%. Reconnect the
RF output connector and increase the power back up to 100% using R75.
This completes the set up of the ALC board and the Forward and Reflected Power
Calibration.
Forward and Reflected Power Calibration of CHV400B and Higher Power
Systems with one or more External Amplifier Trays
NOTE:
If your system is a CHV200B, refer to the previous section for the forward
and reflected power calibration procedures.
Connect a calibrated coupler and average reading power meter to the output of the
DTV mask filter. On the ALC Board (1308570), mounted in the Driver Tray, set the
Switch S1, Auto/Manual ALC, to the Manual position. Refer to Figure 13A. Adjust
the Manual adjustment Pot, R62, for the desired output power level as indicated on
the average reading power meter. In the Amplifier Tray, on the Amplifier Control
Board (1309822), refer to Figure 18; adjust the Forward Calibration Adjustment pot,
R38
OVERDRIVE
THRESHOLD
S1
AUTO/MAN
R75
ALC ADJ
R62
MAN ADJ
J4