A6 Frac-N; A9 Yig Driver; A28 Yig Oscillator (Yo); A29 20 Ghz Doubler - Agilent Technologies PSG Series Service Manual

Troubleshooting
Reference/Synthesis Loop Block Description

A6 Frac-N

One function of the A6 Frac-N is to provide a means to set the YIG Oscillator to any frequency. This is
accomplished on the A6 Frac-N by using a dividing technique that can set the A6 Frac-N VCO signal to any
frequency. The A6 Frac-N VCO output is used as the phase reference for the comparator on the A5 Sampler.
Small changes in the divide number result in small changes in the A6 Frac-N VCO output frequency and
small changes in the YIG Oscillator frequency.
In FM mode, rates 230 Hz and below, FM is accomplished by combining the FM signal and the VCO tune
signal and driving the main coil. For rates above 230 Hz, FM is accomplished using the FM coil circuit on the
A9 YIG Driver and the FM coil in the YIG Oscillator.

A9 YIG Driver

The function of the A9 YIG Driver is to provide the YIG oscillator with the correct power supply and turn
voltages. Coarse tuning s achieved by the A18 CPU setting the pretune DACs to the value needed to tune the
YIG oscillator close to the desired frequency. Correction voltage from the A5 Sampler is summed with the
pretune voltage on the A9 YIG Driver to fine tune the YIG oscillator. For higher rate FM operation, the FM
signal is scaled and the gain calibrated on the A9 YIG Driver before being used to drive the FM coil in the YIG
oscillator.

A28 YIG Oscillator (YO)

The YIG oscillator (YO) output frequency is controlled by the amount of current through the main and FM
coils. The main coil is used for setting CW frequencies and for FM rates 230 Hz and below. The FM coil is used
for rates greater than 230 Hz. The YO operates over a frequency range of 3.2 GHz to 10 GHz.

A29 20 GHz Doubler

Internal to the A29 20 GHz Doubler are two couplers used to pick off some of the 3.2 to 10 GHz signal. One
coupled output is routed to the A6 Frac-N and the other coupled output is routed to the A5 Sampler. The
signal to the A5 Sampler provides the feedback needed to generate the fine tune correction voltage used to
control the accuracy of the YIG oscillator frequency.
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