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Mk5B DOM Phase-cal, State Statistics, and SU Capability

Mk5B DOM Phase-cal, State Statistics, and SU Capability. Roger Cappallo, Brian Fanous Haystack eVLBI Conference 2006.9.18. Mk5B DOM features. 32x32 cross-point switch Delay compensation/tracking to nearest sample Mk4 correlator model packet insertion

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Mk5B DOM Phase-cal, State Statistics, and SU Capability

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  1. Mk5B DOMPhase-cal, State Statistics, and SU Capability Roger Cappallo, Brian Fanous Haystack eVLBI Conference 2006.9.18

  2. Mk5B DOM features • 32x32 cross-point switch • Delay compensation/tracking to nearest sample • Mk4 correlator model packet insertion • 16 tone x 16 ch hi-fi pcal extraction • 16 ch state statistics • VSI-H external interface • Implemented in Xilinx Virtex 2 VP-30

  3. Why use phase cal? • Analog processing of signal from intersection of axes through digitization is dispersive and time-variable • Pcal tones injected into front end serve as phase markers that allow us to subtract out dispersive effects upon channels

  4. Phase cal extractionin the Mk4 correlator • 2 tones extracted by the station unit using 3-level approx. to a sine wave • fourfit uses one of the tones • Additive phases used to precisely align channel phases for coherence • Extracted phases introduce t variable delay; additive phases yield constant delay indistinguisable from the clock setting

  5. Wetzell pcal tone phases

  6. Wetzell pcal amplitudes

  7. Algonquin pcal amps

  8. Algonquin pcal phases

  9. GV difference phases

  10. GV phase residuals

  11. Mk5B phasecal • Implemented in both DIM and DOM • Extracts up to 16 tones from each of 16 channels • Based upon a 256 level data x sinewave product table • Spurious response reduced from 2% to about 2 x 10-5.

  12. Tone Generator

  13. Mk5B phase cal tone shape

  14. (Future) Use of 16 tones in fourfit • Linear fits by channel could use a channel mask or automatic selection by statistical criteria placed on tone amps & phases • Channel to channel variation could obviate the need for a separate single band delay fit • May also be able to eliminate the need for additive pcal offsets, which are time consuming • Multiband ambiguity resolution may be reliable • Could use phase vs. freq to adjust cross power spectra, and increase coherence (and SNR). • However, the Digital Backend development may eliminate the need for extensive pcal processing

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