Chapter 10 533
Synthesizer Section
Unlocked Reference PLL (600 MHz SAWR)
Third LO driver amplifier (600 MHz SAWR)
The third LO driver amplifier (Q503) amplifies the 300 MHz from the
600 MHz phase-lock loop to a sufficient level to drive the LO port of the
double balanced mixer. During the SIG ID operation, (Option 008 only),
diodes CR501 and CR502 turn off the 3rd LO driver amplifier in order
to minimize the amount of 300 MHz going to the double-balanced
mixer.
Check level at amplifier input (steps 1-6)
1. Press
AUX CTRL, INTERNAL MIXER. For Option 008, press SIG ID OFF.
2. Use an active-probe/spectrum-analyzer combination to confirm the
power level of the 300 MHz signal at the following test points:
3. If the signal at A15TP602 is low, but the signal at A15TP504 is
correct, press
AUX CTRL, INTERNAL MIXER. For Option 008, press SIG
ID OFF.
4. Check that PIN diode switches CR603 and CR605 are reverse biased
by approximately +10 Vdc. Refer to function block F of A15 RF
schematic.
5. Measure 300 MHz signal at A15TP503 using an active
probe/spectrum analyzer combination. If the signal is not
approximately +10 dBm, refer to "Unlocked Reference PLL (600
MHz SAWR)" in this chapter.
6. If the level at the TP503 is correct, but signal at TP504 is too low, the
fault is probably in the amplifier.
A15TP602 ≥+7 dBm
A15TP504 ≥+15 dBm
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