C3.10
T856/857 Initial Tuning & Adjustment
M850-00
31/09/98 Copyright TEL
3.7 PA Alignment (T856 Only)
Check that the exciter is connected to the PA with the coaxial link.
Connect an RF power meter to the PA output (use an appropriate attenuator as
necessary).
Turn RV310 (power control) fully clockwise.
Note:
Before the following measurement is taken, ensure the heatsink is at ambi-
ent temperature (20-25°C).
Measure and record the voltage (VL) at L481; perform this measurement at room
temperature so that the NTC (R481) is close to 25°C.
Key the transmitter by earthing the Tx-Key line.
Tune #CV475 until maximum power is obtained. Check that the power exceeds
30W.
Adjust RV310 (power control) to 25W.
Readjust #CV475 to reduce the supply current by up to 0.5A.
3.8 Thermal Shutdown (T856 Only)
Key the transmitter by earthing the Tx-Key line and set the output power to 25W
as described in Section 3.7.
Short L481 to ground.
Set RV330 (shutdown power level) for an output power of 5W.
Set RV320 (shutdown temperature) to 0.16VL volts (measured at IC350 pin 3),
where VL is the voltage measured at L481 in Section 3.7. This sets the thermal
shutdown at 85°C at NTC R481.
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