User Manual

SGD-SB2025NT-TUM, Part 1
Jan 12 Page 56 ALIGNMENT & TESTING
Procedure
3. Remove PA top cover.
4. Measure the resistance of the thermistor between CN4-6 and CN4-4, this should be
approximately 2 kΩ.
5. Connect DC power lead and 10-way connector from SB2025NT.
6. Connect the PA RF output to the RF Power Meter and the PA RF input (CN1) to RF Signal
Generator.
7. Set the Signal Generator to centre frequency of PA under test and reduce the RF drive level
(from signal generator) to zero.
8. Switch on DC power and check that supply is present on L6.
9. Assert PTT (check that no output RF power is emitted from the PA) and check that the
13.8 V supply is switched through to source of TR1 and TR2.
10. With PTT ON, measure the PA bias current at the gates of the Field Effect Transistors
(FETs). The Bias current is band dependent. This is done by monitoring the current drain of
the whole PA with CN1 disconnected.
11. Link the gate of TR2 to GND.
12. Measure current consumption (VHF Low Band 400 mA, VHF High Band 200 mA, UHF
400 mA.) This can be adjusted by RV2. Measure gate volts ≈ 3.4 V.
13. Remove link from TR2.
14. Measure the current consumption and adjust RV1 so that current is 2 Amp total for the VHF
High Band & UHF Band, and 1 Amp for VHF Low Band. Measure gate volts ≈ 3.9 V.
15. With PA transmitting at 50 W into 50 Ω load, measure DC volts FWD power sense CN4-8
and REFL power sense CN4-5. These voltages should be approx. 2.8 V and <250 mV
respectively.
16. Reduce the RF drive until the PA output is 10 W. Disconnect the PA RF output cable.
17. Measure the DC voltage on CN4-8 and CN4-5 again. These should now both read lower
approximately 1 V.
18. Remove PTT.
6.2.4 VCO Board
Test Equipment Required
• Tested SB2025NT with Exciter VCO removed.
• PC with MxTools software installed.
• RF Communications Test Set.
• Multimeter.
• Oscilloscope.
• +13.8 VDC Power Supply.