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7-3 ANALOG SUBSYSTEM
ASSEMBLIES
The following paragraphs briefly describe the major assemblies that com
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prise the 373XXA Analog Subsystem. Descriptions of the functions per
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formed by each assembly are also included.
Signal Source Module The Signal Source Module consists of the items listed below; refer to the
block diagram of the Analog Subsystem (Figure 7-2) at left.
q
2-20 GHz YIG Oscillator Assembly
q
A21A1 YIG/Bias Controller PCB
q
A21A2 Source Control PCB
q
Switched Filter Assembly
q
Down Converter Assembly
The Signal Source Module is a swept frequency signal generator that
produces a phase locked (and leveled) output signal within a range of
22.5 MHz to 20 GHz. All Series 373XXA VNA models employ
phase-lock control of the signal source module so that the output fre-
quency is accurate and stable. The output signal is phase locked by
the –6 MHz/volt control signal fed back from the A8 Source Lock/Sep-
aration Control PCB Assembly (which is described in following para-
graphs).
All Series 372XXB VNA models use a single YIG-tuned oscillator to
produce fundamental frequency source signals from 2.0 to 20 GHz. All
other output frequencies are derived from the fundamental frequen-
cies generated by the YIG-tuned oscillator. The signal source output
frequencies for the low end portion of the frequency range (22.5 MHz
to 2.0 GHz) are produced by down converting YIG fundamental signals
in the range of 6.3225 to 8.3 GHz.
For Model 37369A, the signal source output frequencies for the high
end portion of the frequency range (20 to 40 GHz) are produced by the
Switched Doubler Module that doubles the YIG fundamental signals
in the range of 10 to 20 GHz. The Switched Doubler Module (SDM) is
located in the Test Set Module (described below.) The A21A2 Source
Control PCB assembly provides all bias and control signals for the
SDM.
The YIG-tuned oscillator generates a high-power RF output signal
that has low broadband noise and low spurious content. The frequency
of the YIG-tuned oscillator is controlled by means of :
q
The YIG main tuning coil
q
The YIG FM (fine tuning) coil
The system A9 Main Microprocessor PCB sends the data that repre
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sents the desired operating frequency to the A21A2 (Source Control)
PCB, which converts the frequency data to analog signals. These sig
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SYSTEM DESCRIPTION ANALOG SUBSYSTEM ASSEMBLIES
373XXA MM 7-7