MXi005U OPERATIONS AND MAINTENANCE
4
4.1
4.1.1
4.1.2
4.1.3
TEST
AND
TROUBLESHOOTING
B
ENCH
T
EST
P
ROCEDURES
The following procedures are test instructions for the amplifier modules comprising the MXi amplifier.
Front-End Module Bench Test Procedure
•
Connect a +28V (1A current limit) power supply to TP2.
•
Apply a 0dBm (1mW) RF input to the amplifier.
•
Turn RV2 fully clockwise. The front-end should have a gain of 13dB. Adjusting RV2 from one extreme to
the other should vary the gain by a minimum of 20dB. Set RV2 fully clockwise.
•
RF Mute Check: Connect a variable supply to TP1. Gradually increase the voltage until the gain drops by
20dB or more. The applied voltage should be approximately 7 volts.
•
Telemetry: Monitor TP3. Note voltage decrease to 0V DC when RF output has been muted.
IPA1 Bench Test Procedure
This amplifier must be mounted on a properly sized heatsink for testing.
•
Connect a suitable load to the output of the Pre Amplifier.
•
On the unit under test, set RV200 fully clockwise and set RV110 fully counter-clockwise.
•
Set variable power supply to 28.0V and set its current limit to 1 ampere.
•
Apply the +28V to the feed through capacitor of the pre-amp shield box.
•
Adjust RV3 to achieve 6.5
±
0.2V at the junction of R5 and RV100.
•
Adjust RV200 to achieve total current draw of 300
±
20mA.
•
Check that the junction of R100 and CR100 measures between 3.5 and 5.5 volts.
•
Adjust RV110 to raise total current draw to 600
±
50mA.
•
Check that the junction of R110 and CR110 measures between 3.5 and 5.5 volts.
•
Increase the power supply current limiting to 2.2A.
•
Increase RV3 clockwise slowly and check that the maximum current limits itself at 1.6
±
0.1 Amp but do
not allow current to go above 2A while performing this test.
•
Reset RV3 to achieve 6.5
±
0.2V measured at the junction of R5 and RV100.
•
Check balance of the two transistors with a voltmeter connected between the hot sides of C105 and
C115; the difference in voltage should be less than 3mV.
•
Apply RF drive (max. +18dBm from a pre-amp) and adjust C101, C103, C111, and C113 for minimum
frequency response ripple and flat response. Gain should be a minimum of 15dB with maximum variation
less than 0.5dB over the frequency range 470 MHz through 860 MHz (Note: output will then be about
+33dBm or 2 Watts for an input of +18dBm, so make sure you properly protect your test equipment).
•
If roll off at the higher frequencies prevents meeting this gain-bandwidth specification, it may be
necessary to replace either C103 or C113 or both with a higher value; use variable capacitor made by
Johanson, part # 16E2320-2, which is 2.5 to 10pF.
Pallet 21B1751 Bench Test Procedure
•
BIAS SETTING: Connect a 50-Ohm load to the output of the pallet.
•
Before ap28V to the module, adjust R12 fully clockwise. Limit the power supply current to 3.0A.
PUB06-76 Rev 2 July 18, 2007
06-76-10
MXi005U Operations and Maintenance
