122 Chapter 5
Troubleshooting the Synthesizer Section
A9 Second LO/Fan Control Assembly Description
A9 Second LO/Fan Control Assembly
Description
Second LO Circuitry
Purpose. The A9 second LO assembly generates the 3.9 GHz LO signal
that is used by the A20 low band assembly to generate the low band
second IF signal of 321.4 MHz. The A9 board also contains unlock
detection circuitry, that indicates an unlock condition when it occurs on
the assembly.
Signal Path. The 600 MHz signal from the A11 reference assembly is
routed to a phase detector that compares the phase of the 600 MHz
signal with the output of the PMYO.
Fan Control Circuitry
Purpose. The three fans used to cool the various assemblies in the
instrument are controlled through circuitry located on the A9 assembly.
The speed of the fans varies with changes in internal instrument
temperature; as temperature increases, fan speed increases. The
front-panel line switch, that turns the power supply on and off, is input
from the A9 assembly fan control circuitry. An over-temperature circuit
is provided that will turn off the instrument if an over-heating
condition in the instrument occurs.
Interconnections to other assemblies
• A9J1 600 MHz input from A11 Reference assembly
• A9J10 3.6 GHz output to A20 Lowband assembly
• A9J11 and J12 Trigger outputs to rear panel
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