Glenayre GL-T8541, Руководство пользователя, Страница: 62 / 90

GL-T8541 PA Glenayre Document Number: 9110.01002
CHECKOUT AND MAINTENANCE 09/10/99
Page: 7-8 Copyright © 1997 Glenayre
7.7 Setting PA Module Bias and Idle Current
To insure correct performance of the GL-T8541 Transmitter, the bias must be set correctly
for each transistor on the driver and PA boards. The bias must be set after a transistor on a
board has been replaced, or an amplifier board has been replaced.
Terminate the PA output in an RF test load capable of at least 250 watts (or the antenna)
before checking or setting the PA bias.
7.7.1 Checking Bias Settings
Using the exciter VDT readout, a quick check of the bias settings for the amplifier boards
can be performed as follows.
1. Unkey the transmitter and remove all power.
2. Terminate the transmitter into a high power (at least 250 watt) RF test load.
3. Disconnect the exciter RF output cable.
4. Apply power to the transmitter.
5. Driver board Q1 idle current flows when dc power is applied, but its value is usually
too small to cause a reading on the VDT. The driver current is 20 - 50 mA.
The idle current of driver board Q1 can be measured with a meter, this measurement
procedure will be covered in the next section.
6. Enter the forward power calibrate mode and key the transmitter (key sequence 6>1).
7. The driver idle current should be 1.0 +/-0.5A.
8. The VDT current display for each PA board should show 2.0 +/-0.5A.
9. Unkey the transmitter and press the escape key or “m” to exit the calibration mode.
10. Remove all power and reconfigure the transmitter for normal operation.
7.7.2 Checking Driver Q1 Bias Setting
Driver board current is usually too small to cause a reading on the VDT, but it can be
checked using the following procedure:
1. Unkey the transmitter and remove all power.
2. Terminate the transmitter into a high power (at least 250 watt) RF test load.
3. Disconnect the exciter RF output cable.
4. Remove PA module from transmitter and remove the outer and inner PA covers.
5. Remove or relocate equipment as necessary to gain access to PA boards while PA
module is installed. Exciter must remain connected to metering board and dc power
source. Reinstall PA module leaving RF input disconnected.
6. Check driver board Q1 idle current using the following sub-routine:
A. Remove JW1 from the driver board.
B. Connect a current meter between test points TP1 and TP2.
C. Apply power to the transmitter, but do not key it.