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Phase cal extraction in the Mk4 correlator

Phase cal extraction in 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

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Phase cal extraction in the Mk4 correlator

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  1. 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

  2. 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.

  3. Mk5B phase cal tone shape

  4. Wetzell pcal tone phases

  5. Wetzell pcal amplitudes

  6. Algonquin pcal phases

  7. Algonquin pcal amps

  8. GV difference phases

  9. GV phase residuals

  10. (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 • 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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