Mk5B DOM Phase-cal, State Statistics, and SU Capability Roger Cappallo, Brian Fanous Haystack eVLBI Conference

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

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

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 Extracted phases introduce t variable delay; additive phases yield constant delay indistinguisable from the clock setting

Wetzell pcal tone phases

Wetzell pcal amplitudes

Algonquin pcal amps

Algonquin pcal phases

GV difference phases

GV phase residuals

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

Tone Generator

Mk5B phase cal tone shape

(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