Mk5B DOM Phase-cal, State Statistics,
and SU Capability
Roger Cappallo, Brian Fanous
Haystack eVLBI Conference2006.9.18
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 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
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 10-5.
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
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