Technical Manual Appendices
© SPECTRA ENGINEERING 2006 Revision 4.2.3
127
8.1.2 PA Module Test Procedure
Test Equipment:
Tested MX800 with PA removed
PC with MXTOOLS software
RF Power Meter
RF Signal Generator
Multimeter
+13.8VDC 15A power supply
Preliminaries:
Program upper, middle and lower frequencies of band into 3 channels in
MXTOOLS channel screen. Although the PA will function over a wider
bandwidth, the nominal switching bandwidth of the PA is 10MHz. The
recommended procedure is to centre this 10MHz around the centre of the user
frequencies. (Note that 'Continuous Update Enabled' on the MXTOOLS
channel screen should be ticked for these tests)
Do not connect Exciter RF drive output CN1 to PA.
Procedure:
1. Remove PA top cover. Measure resistance of thermistor between CN4-
6 and CN4-4, this should be approximately 2kΩ. Connect DC power
lead and 10-way connector from MX800. Connect PA RF output to RF
power meter and PA RF input (CN1) to RF signal generator.
2. Set signal generator to centre frequency of PA under test and reduce RF
drive level (from signal generator) to zero. Switch DC power on and
check that supply is present on L9. Assert PTT (check that no output RF
power is emitted from the PA) check that the 13.8V supply is switched
through to the Hybrid on pin adjacent to RF input and that 5V is
switched to the Hybrid on the next pin along (pins not numbered on
Hybrid).
3. With PTT ON measure the PA bias current at the Gates of the FET’s.
The Bias current is band dependent. This is done by monitoring the
current drain of the whole PA with CN1 disconnected. Link the gate of
TR2 to GND. Measure current consumption (VHF High Band 200mA
,UHF 400mA.) This can be adjust by RV2. Measure gate volts ≈ 3.4V
Remove link from TR2. Measure current consumption, adjust RV1 so
that current is 2Amp total (VHF & UHF). Measure gate volts ≈ 3.9V
4. With PA transmitting at 50W into 50Ω load measure DC volts FWD
power sense CN4-8 and REFL power sense CN4-5. These voltages
should be approx. 2.8V and <250mV respectively. Reduce RF drive
until PA output is 10W and disconnect PA RF output cable. Measure
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