Walsh Function Definition for ALMA Abstract
Return to Memo list
ALMA Memo # 565
Walsh Function Definition for ALMA
Darrel Emerson
2007-02-02
ALMA has chosen to use a set of 128 orthogonal Walsh functions, both for the sideband separation using 90-degree phase switching at the first local oscillator, and for spurious rejection using 180- degree phase switching at the first local oscillator with demodulation by means of a digital sign change shortly after the digitizer. A set of orthogonal Walsh functions can be defined and ordered in many different ways (PAL, Natural or Paley ordering, WAL, CAL & SAL sequency ordering) and with different phasing definitions (e.g. Harmuth phasing, or "positive phasing".) It is proposed here that ALMA standardize on a set of Walsh functions in WAL order with positive phasing. A numerical table is included, and is available in machine readable form.
View a pdf version of ALMA Memo #565.
