SPW /FREQUENCY

    [NOEMAOFFLINE\]SPW /FREQUENCY Fcent dF

    Define a spectral window from Fmin=Fcent-dF/2 to Famx=Fcent+dF/2 in  the
    current  frequency frame (as defined with SET FREQUENCY command).  Fcent
    and dF must be in GHz.  Fmin and Fmax must be in the same baseband.