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Round Trip Phase Measurement System

This project outlines requirements, considerations, and temperature effects for a measurement system focusing on IF phase stability analysis, with emphasis on fiber cable wrap, laser/electronics stability, and dispersion in the fiber.

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Round Trip Phase Measurement System

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  1. Round Trip Phase Measurement System Terry Cotter EVLA LO/IF PDR 22-23 January 2002

  2. Requirements • IF Phase Stability Requirements • Short Term <.5ps rms for times <1s • Long Term <6ps linear slope over 30min • IF Phase shift with pointing change • <.7ps across whole sky • <.07ps per degree of slew * specs apply after any RTP correction EVLA LO/IF PDR 22-23 January 2002

  3. Considerations • Fiber cable wrap • Needs to twist fiber not stretch it • Temperature effects on fiber • burial depth • insulating/temperature stabilizing exposed fiber • Laser/electronics stability • Dispersion in the Fiber EVLA LO/IF PDR 22-23 January 2002

  4. Temperature Considerations From EVLA Memo 10 Based on Duhamel’s theorem EVLA LO/IF PDR 22-23 January 2002

  5. Temperature Considerations Bottom line: For just the part buried @1m • Long term stability is .4 ps/s which meets the spec of 1.4 ps/s • Short term stability is .0002 ps/s which far exceeds the spec of .5 ps/s EVLA LO/IF PDR 22-23 January 2002

  6. Temperature Considerations • Do we really needs Round Trip Phase Correction? • YES • Long term stability is near Spec • Short term above ground and in the building • Good monitor of system problems EVLA LO/IF PDR 22-23 January 2002

  7. Other Considerations • Laser Stability • Unknown as to how much of a problem this is going to be • Dispersion in the fiber • Will need to operate RTP system near zero dispersion point of the fiber ~1310nm EVLA LO/IF PDR 22-23 January 2002

  8. EVLA LO/IF PDR 22-23 January 2002

  9. Side Note Two master rack are required, one for back up Round trip phase equipment can be used to monitor the master racks together. EVLA LO/IF PDR 22-23 January 2002

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