Delay Errors in Single/Double-SB Interferometer Systems Abstract
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ALMA Memo # 561
Delay Errors in Single- and Double-Sideband Interferometer Systems
A. R. Thompson, L. R. D'Addario, D. T. Emerson, P. J. Napier
2006-09-20
In ALMA and most other large synthesis arrays, the instrumental delays that are inserted to compensate for the varying geometric delays are implemented digitally and are variable in increments of fixed minimum value. The incremental nature of the delays results in phase errors that are periodic functions of time that can degrade the signal-to-noise ratio, i.e. the sensitivity of the instrument. Considerations for single- and double-sideband (SSB and DSB) receiving systems are different in some important details. This memorandum is concerned with specification of the minimum delay increments so that the degradation is no more than approximately 1%. It also includes consideration of methods of mitigation that can reduce the effect of the phase errors. Without mitigation, a minimum increment of 1/16 of the sample interval (1/32 of the reciprocal bandwidth) is considered to be satisfactory for ALMA.
View a pdf version of ALMA Memo #561.
