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3. Theory of Operation
Introduction
This chapter describes assembly-level operating principles for the 5071A
Primary Frequency Standard and is divided into three sections. All three
sections of this chapter are organized around functional concepts and the
direction of signal flow into, within,
and out-of the instrument/assemblies/modules. Because of this, the
presentation of assemblies and modules may not occur in ascending order of
reference designation number.
All references to internal-battery power, battery status or battery operation,
do not apply for 5071A Option 048. Option 048 does not have an internal
standby battery.
Basic Operating Principles
The operation of the 5071A Primary Frequency Standard is based on
matching the frequency of a synthesized microwave probe signal to the
hyperfine resonance in the ground state of the cesium atom. This resonance
is the basis for the internationally accepted unit of time.
In operation, the frequency of a nominal 10 MHz crystal oscillator is
multiplied by the correct fixed rational number (frequency synthesis process)
to achieve the cesium resonance frequency at 9.192... GHz. This
synthesized frequency is compared (as described later), in a cesium atomic
beam tube to the actual cesium resonance, creating
an error signal proportional to its difference from the true resonance
frequency.
This error signal is processed and fed back to control the 10 MHz crystal
oscillator's actual frequency reducing the error to zero. Thus, if the rational
number is properly chosen and there are no distortions of the cesium
resonance, the crystal oscillator is directed to run at exactly 10 MHz. All
outputs from the 5071A are derived from this controlled 10 MHz crystal
oscillator.
Note
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