Symmetricom 5071A, Assembly And Service Manual

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3. Theory of Operation
Simplified Functional Description
129
Analog Signal Chain Block
The CBT output signal is amplified by the analog signal chain and converted
into digital samples that are fed to the microprocessor (via VFC/VFC clock
lines) in the instrument control block. The microprocessor uses the samples
to calculate corrections to the microwave probe signal frequency and
amplitude.
The main frequency servo loop is completed by changing the frequency of
the reference oscillator in the reference oscillator/RF chain block as required.
The analog signal chain block consequently generates an Electronic
Frequency Control (EFC) signal routed back to the reference oscillator/RF
chain block.
Input/Output Block
The input/output (I/O) block generates the instrument's rear panel RF output
signals which are phase-coherent with signals in the RF chain. The I/O block
receives two low-noise 80 MHz signals from the reference oscillator/RF chain
block. These 80 MHz signals are used to create the instrument's 1PPS and
sine-wave outputs. When the microwave probe signal is at correct frequency
and amplitude, the I/O block will synthesize the exact nominal output
frequencies.
The block also receives a front or rear panel Sync-input signal to synchronize
the 1 pps outputs with an external system or event. The 1PPS output pulse
signals are derived by division. The phase of the 1PPS output pulses may be
adjusted in 50 ns units.
Power Supply Block
The power supply block provides the instrument with required internal dc
power from either ac power, an internal standby battery (Opt. 048 does not
have an internal standby battery) , or an external dc power source. It monitors
the presence of these power sources, switching from one to another as
required. In addition, this block (except in Opt. 048) maintains the internal
standby battery charge when ac power is present.