Installation guide

Troubleshooting
Block Descriptions for Option 501, 502, 503, 504
1-120
Frequency Synthesis Block Description for Option 501, 502, 503, 504
Overview
Frequency synthesis for Option 501, 502, 503, 504 signal generators is made from portions of the following:
• A18 Reference (Option 501, 502, 503, 504)
or A18 Reference (Option 501, 502, 503, 504 with Option 1E5)
• A17 Synthesizer (Option 501, 502, 503, 504)
• A13 Output (Option 501, 502, 503, 504 or Option UNJ)
or A13 Output (Option UNB)
• A23 Motherboard
The Frequency Synthesis Block consists of the A18 Reference and the A17 Synthesizer. Frequency synthesis
begins on the A18 Reference with a 10 MHz reference. The A18 Reference has a
Temperature Compensated Xtal Oscillator (TCXO), while the high stability timebase, A18 Reference
(Option 501, 502, 503, 504 with Option 1E5), has an Oven Controlled Xtal Oscillator (OCXO). Both references
may be phase locked to an external reference or operate stand-alone. The 10 MHz reference phase locks a 1
GHz discrete oscillator on the A18 Reference. The frequency accuracy of the 10 MHz reference is translated to
the final output frequency accuracy. The 10 MHz signal is distributed throughout the signal generator. In the
following description, the main focus will concentrate on the 10 MHz going to the A17 Synthesizer, but the 10
MHz is also routed to the Internal Modulation Source Function Generator located on the A23 Motherboard
and routed to the rear panel. The 1 GHz is routed to the heterodyne circuit located on the A13 Output.
The 10 MHz reference is part of a Phase Lock Loop (PLL) circuit located on the A17 Synthesizer. The PLL
tunes a Voltage Controlled Oscillator (VCO), which is divided or multiplied to achieve the final RF output
frequency.
A18 Reference
Essential to frequency accuracy and low phase noise are clean and stable reference signals. The reference
signals on the A18 Reference are a 10 MHz TCXO or OCXO and a 1 GHz discrete oscillator. To minimize
frequency drift, the 10 MHz TCXO is tuned by a DAC and the OCXO has an oven to maintain a constant
crystal temperature.
If a signal generator with an A18 Reference (Option 501, 502, 503, 504 with Option 1E5) has been without
electrical power, a "Reference Oven Cold" warning is displayed when the signal generator is powered on. The
warning message is controlled by a timer and should go out after five minutes of being connected to ac power.
The 10 MHz reference may be phase locked to an external 2, 5, or 10 MHz reference. The 10 MHz reference is
available at the signal generator's rear panel and may be used to phase lock other instruments in a system.
The 10 MHz reference is routed to the A17 Synthesizer and is part of a PLL which is used to tune a VCO.
The 1 GHz discrete oscillator is split into two paths. One path is divided down to 10 MHz and is then phase
compared to the 10 MHz signal from the A18 Reference; the difference of this comparison is used to drive an
integrator which in turn is used to tune the 1 GHz oscillator and ensure both reference signals are phase
locked together. The other path of the 1 GHz signal is routed to the A13 Output.
A17 Synthesizer (Option 501, 502, 503, 504)
The A17 Synthesizer generates the final RF output frequency. Two proprietary application specific
integrated circuits (ASIC), named Paren and Tesera, are used to tune a VCO on the