Agilent Technologies HP 8719D Service Manual page 340

Figure 12-3. Source Functional Group, Simplified Block Diagram
The subsweep sequence takes place in the following steps. The paragraphs
below describe the details of this process, and provide additional information on
the assemblies in the source group.
1. The source is pretuned low. The source signal (SOURCE OUT) is fed to the R
sampler.
2. A signal (VCO OUT) is generated by the VCO in the fractional-N synthesizer.
3. A comb of harmonics (1st LO) is produced in the pulse generator.
4. A synthesizer harmonic (1st LO) and the source signal (SOURCE OUT) are
mixed in the sampler. A difference frequency (1st IF) is generated.
5. The 1st IF signal from the R sampler is fed back and compared to a
reference. A tune current is generated.
6. The tune current is used to set the frequency of the source YIG oscillator.
7. Phase lock is acquired and a synthesized subsweep is generated. The source
tracks the synthesizer.
Theory of Operation 12-13