Giga-tronics GT 9000, Operation & Maintenance Manual

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3.2.4 Dual-Loop Indirect Synthesis
The output of a synthesized signal generator is phase-locked to a stable reference signal, such as
that produced by a crystal oscillator to give the generator output the stability and accuracy of
the reference. However, this can be difficult to achieve in broad-band generators.
Giga-tronics employs a dual-loop synthesis technique to produce stable and spectrally pure
frequencies over a wide frequency range. The two loops are (1) the output loop, which
phase-locks the synthesizer output frequency to a reference frequency, and (2) the reference
loop, which phase-locks the reference frequency to the timebase. The timebase or master
reference is a highly stable 10 MHz source built into the instrument. An external source can be
easily substituted for it at the option of the user (see Figure 3-5).
Figure 3-5. The output loop
Theory of Operation
Manual No. 120AM00250, Rev C, September 1998
3-5