Broadcast Electronics FM-5T, User Manual

Page: 163 / 191

2-9
WARNING: DISCONNECT POWER PRIOR TO SERVICING
2-93. Refer to OUTPUT POWER METER CALIBRATION in the following text and perform the
procedure to calibrate the output power meter.
2-94. Remove the test equipment and return the transmitter to service.
2-95.
OUTPUT POWER METER CALIBRATION.
This adjustment will be required only if the
OUTPUT POWER meter or potentiometer R113 is replaced. To adjust output meter cali
brate control R113, proceed as follows.
2-96. Required Equipment. The following equipment is required to adjust the output meter cali
brate control.
A. 1/16 inch jewelers screw-driver, flat-tip.
B. Test load and connecting line (50 Ohm non-inductive, 1 5/8 inch line input, 5 kW
minimum).
C. Calibrated in-line wattmeter with 1 5/8 inch sampling section and cables (Bird
4720 Thruline with 5 kW element or equivalent).
2-97. Procedure. To adjust the control, proceed as follows:
2-98. Check and adjust forward power calibration control R83 before proceeding (refer to FOR
WARD POWER CALIBRATION in the preceding text).
WARNING
WARNING
DISCONNECT ALL TRANSMITTER PRIMARY POWER
BEFORE PROCEEDING.
2-99. Disconnect the transmitter primary power.
2-100. Connect the test load and wattmeter to the transmitter output.
2-101. Apply power and operate the transmitter in the local manual mode ( REMOTE DISABLE
illuminated, APC ON extinguished) at the desired 100% RF power output as indicated by
the in-line wattmeter.
2-102. Refer to Figure 2-1 and adjust meter calibration control R113 to obtain a 100% OUTPUT
POWER meter indication.
WARNING
WARNING
ASSURE ALL PRIMARY POWER IS DISCONNECTED
BEFORE PROCEEDING.
2-103. Disconnect primary power.
2-104. Remove the test equipment and reconnect the transmitter output to the antenna load.
2-105.
REFLECTED POWER CALIBRATION.
Potentiometer R84 calibrates the reflected power
sample circuit and potentiometer R119 nulls the VSWR meter. Adjustment is required
only if repairs have been made to the directional coupler reflected port, controller main cir
cuit board, or low-pass filter. To adjust the control, proceed as follows.
2-106. Required Equipment. The following equipment is required to adjust the controls.
A. 1/16 inch jewelers screw-driver, flat-tip.
B. 10 dB attenuator, BNC connections.
C. 5/16 inch nut-driver.