A14/A13 Fractional-N; A12 Reference; A7 Pulse Generator; A11 Phase Lock - HP 8753D Option 011 Service Manual

band is not phased locked nor does it use the ALC. It is the basic ampli ed output of the
fractional-N synthesizer.
The source functional group consists of the individual assemblies described below.

A14/A13 Fractional-N

These two assemblies comprise the synthesizer. The 30 to 60 M z VCO in the A14 assembly
generates the stable LO frequencies for fundamental and harmonic mixing.

A12 Reference

This assembly provides stable reference frequencies to the rest of the instrument by dividing
down the output of a 40 M z crystal oscillator. In low band operation, the output of the
fractional-N synthesizer is mixed down in the A12 reference assembly. (The 2nd LO signal
from the A12 assembly is explained in Receiver Theory.) The A12 is also the origin of the
super low band portion of the 8753D source.

A7 Pulse Generator

A step recovery diode in the pulse generator produces a comb of harmonic multiples of the
VCO output. These harmonics provide the high band LO (local oscillator) input to the
samplers. In low band and super low band the operation the pulse generator is turned o .

A11 Phase Lock

This assembly compares the rst IF (derived from the source output in the A4 sampler) to a
stable reference, and generates an error voltage that is integrated into the drive for the A3
source assembly.

A3 Source

This assembly includes a 3.0 to 6.8 G z YIG oscillator and a 3.8 G z cavity oscillator. The
outputs of these oscillators are mixed to produce the RF output signal. In Option 006 (30
k z to 6 G z) the frequencies 3.0 to 6.0 G z are no longer a mixed product, but are the
direct output of the YIG Oscillator. The signal tracks the stable output of the synthesizer.
The ALC (automatic leveling control) circuitry is also in the A3 assembly.
12-10 Theory of Operation RAFT
3/21/106 15:14
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