Notes

Outline

OVSA Experience of Relevance to FASR Frequency-Agile Interferometry

Outline of Talk Quick Overview of OVSA Multi-frequency calibration Simplifications Complications Conclusions

Quick Overview of OVSA 7 Antennas 2 large (27 m) 5 small (2 m) Frequency Agile Tune in any sequence to any of 86 frequencies in range 1-18 GHz 10 ms sample time (takes 8 s to tune to 40 frequencies in each of RCP and LCP)

Slide 4

Outline of Talk Quick Overview of OVSA Multi-frequency calibration Simplifications Complications Conclusions

Multi-frequency Calibration The system phase on each individual baseline is random with frequency

Multi-frequency Calibration II However, the difference in phase for a given baseline, from one time to the next, follows a linear frequency dependence.

Outline of Talk Quick Overview of OVSA Multi-frequency calibration Simplifications Complications Conclusions

Slide 9

OVSA Example Calibrate once every 2 hours Ref calibration

Outline of Talk Quick Overview of OVSA Multi-frequency calibration Simplifications Complications Conclusions

Slide 12

Slide 13

Outline of Talk Quick Overview of OVSA Multi-frequency calibration Simplifications Complications Conclusions

Conclusions for FASR Take advantage of the smoothness of most frequency-dependent phase changes. Expect phase changes ~f  for atmosphere and cables, ~f -2 for the ionosphere.  Frequency-independent phase offsets are also possible. Lobe ambiguities need not be a driver for time between phase calibrations (although linearity of phase changes will be). Care must be taken to calibrate frequency-to-frequency amplitudes (self-cal is no help).