250 N9030B PXA Signal Analyzer Service GuideLO Synthesizer/Reference TroubleshootingA14 LO Synthesizer Assembly DescriptionA14 LO Synthesizer Assembly DescriptionPurposeThe L.O. Synthesizer assembly provides the power and drive to the A20 YTO(YIG Tuned Oscillator). The A20 YTO is used as the 1st Local Oscillator (1st LO)in the A13A1 Front End Assembly for RF conversion. The A13A1 Front Enddistributes the 1st LO to the various mixers and to the A14 LO Synthesizer forpurposes of phase locking the 1st LO. The frequency range of the 1st LO is 3.8to 8.73 GHz.The RF input signal mixes with the 1st L.O. in one of three possible mixers onthe A13A1 Front End Assembly. For more detailed description on the Front EndAssembly, see Chapter 4, “RF Section Troubleshooting (RF/MicrowaveAnalyzers)” in this service guide.The A14 LO Synthesizer has the following inputs and outputs:— Power Supply inputs— Serial Bus input for LO Control— Sweep input for LO Control— 4800 MHz input signal from A16 Reference Assembly— 100 MHz input signal from A16 Reference Assembly— 1st LO output signal from A13 RF Front End Assembly— Power and drive signals to the A20 YTOThe input signals to the LO Synthesizer Assembly are the 4800 MHz and 100MHz reference signals from the A16 Reference Assembly. These signals areused to phase lock the offset loop on the A14 and the 1st LO. On the A16Reference Assembly, both the 4800 MHz and 100 MHz reference signals arephase locked back to the 10 MHz reference, which is also located on A16.The quality of the phase lock design that locks the 1st LO has a directrelationship on the overall stability of the analyzer. Users can also provide theirown external reference. The frequency accuracy of the user's frequencyreference is directly related to the overall frequency accuracy of the signalanalyzer.
