BACKEND FTS

###
BACKEND FTS

        FTS                         ! Fourier Transform Spectrometer

        The FTS supports two modes:
         -  wide bandwidth, up to ~ 4000 MHz on EMIR (~ 1000 MHz on HERA),
            with a resolution of ~ 0.195 [MHz], or
         -  fine resolution, ~ 0.049 MHz,
            with a bandwidth up to 1820 MHz on EMIR (~ 500 MHz on HERA)

        All parts of the FTS must use the same resolution.

        NOTE: EMIR subbands, IF cables, and Backends

        The output signals from EMIR are transmitted to the spectrometers and
        NBC through 8 IF cables. Each IF cable carries one subband of bandwidth
        4 GHz. This subbands are LO, LI, UI, or UO.

        NBC, 4MHz, WILMA, and VESPA can only(!) be connected to IF cables 1 to 4.
        FTS parts 1 to 4 can also be connected to IF cables 1 to 4.

        The command options RECEIVER /HORIZONTAL and RECEIVER /VERTICAL allow
        to select up to 4 EMIR subbands that will be transmitted through IF
        cables 1 to 4 (compare HELP RECEIVER /HORIZONTAL and the EMIR user
        documentation). This selection can include Outer subbands.

        In addition, the IF cables 5 to 8 carry the 4 Outer subbands
        corresponding to the subbands selected for IF cables 1 to 4. E.g., if
        we select for IF 1 to 4:
        E230 ver UO    E090 ver UI    E230 hor UI   E090 hor UI
        then the IF cables 5 to 8 will transmit:
        E230 ver UO    E090 ver UO    E230 hor UO   E090 hor UO.

        Only FTS parts 5 to 8 can be connected to IF cables 5 to 8.

        BACKEND NBC|WILMA|FTS /DEFAULT will automatically set the maximum
        number of backend parts for all available subbands.

        BACKEND BBC is completely independant of the sub band selections for
        the IF cables.

        NOTE: bandwidth selection with EMIR

        The pako command already allows some flexibility that is not yet fully
        supported by the data handling, e.g., to select only part of the full
        bandwidth.

        NOTE: FTS on HERA

        With HERA, the FTS can be connected to HERA1 and/or HERA2.

        On HERA, the FTS provides some extra bandwidth, which is not
        symmetrical to the point where the line (the commanded frequency) gets
        centered.

        With HERA /width wide, the line gets centered at the center of WILMA
        and 4MHz.  Relative to this point, the FTS in wide mode covers IF
        offset frequencies from < -512 to > +512. In pako the nominal value of
        the bandwidth is 1024, symmetric around the line.

        With HERA /width narrow, the line gets centered at the center of
        VESPA.  Relative to this point, the FTS in fine mode covers IF offset
        frequencies from < -256 to > +360. In pako the nominal value of the
        bandwidth is 512, symmetric around the line.

        It is also possible to connect FTS in fine mode on HERA /width wide or
        FTS in wide mode on HERA /width narrow.  However, in these cases the
        FTS band coverages are very asymmetric to the line. (See HERA and FTS
        documentation for the exact details of the IF ranges).