Agilent Technologies HP 8719D Service Manual page 344

Source Block: The YIG Oscillator Signals
The source block includes two YIG oscillators and a 3.8 GHz hxed oscillator.
The outputs of these oscillators produce the source signal. In phase-locked
operation, this signal tracks the stable output of the synthesizer. Figure 12-4
illustrates the assemblies in the source block.
Figure 12-4. Simplifled Diiram of the Source Block
The YIG oscillator has a main coil and an FM coil. These are analogous to
the woofer and the tweeter in a stereo speaker: the woofer reproduces low
frequencies and the tweeter reproduces high frequencies Similarly in the YIG
oscillator, the main coil allows large, slow changes in frequency but cannot
respond to high frequency deviations, which are sent to the faster-acting FM
coils.
The tune current from the All phase lock assembly splits into two paths. One
path is lowpass liltered, removing high frequency components, and goes to the
YIG main coil; the other path is highpass filtered, removing low frequency
components, and goes to the YIG FM coils. The filters are matched in stop-band
response, such that one picks up where the other leaves off.
Theory of Operation 12-17