Each row of the RX_CAL_INFO binary table holds the receiver and calibration temperatures at the indicated frequency under the conditions described by the header keyword values. The EXTVER keyword distinguishes this extension from other RX_CAL_INFO binary tables in the file as described in section 2.1 General (item 4) in the GBT Software Project Note 4.0, ``Device and Log FITS Files for the GBT.''
XTENSION= 'BINTABLE' / binary table extension BITPIX = 8 / 8-bit bytes NAXIS = 2 / 2-dimensional binary table NAXIS1 = 16 / width of table in bytes NAXIS2 = 175 / number of rows in table PCOUNT = 0 / size of special data area GCOUNT = 1 / one data group (required keyword) TFIELDS = 4 / number of fields in each row TTYPE1 = 'FREQUENCY' / label for field 1 TFORM1 = '1E ' / data format of field: 4-byte REAL TUNIT1 = 'Hz ' / physical unit of field TTYPE2 = 'RX_TEMP ' / label for field 2 TFORM2 = '1E ' / data format of field: 4-byte REAL TUNIT2 = 'K ' / physical unit of field TTYPE3 = 'LOW_CAL_TEMP' / label for field 3 TFORM3 = '1E ' / data format of field: 4-byte REAL TUNIT3 = 'K ' / physical unit of field TTYPE4 = 'HIGH_CAL_TEMP' / label for field 4 TFORM4 = '1E ' / data format of field: 4-byte REAL TUNIT4 = 'K ' / physical unit of field EXTNAME = 'RX_CAL_INFO' / name of this binary table extension EXTVER = 3 / extension version TESTDATE= '2001-06-20' / date test data acquired RECEPTOR= 'XL ' / source of IF signal FEED = 1 / feed identifier POLARIZE= 'X ' / channel's polarization BANDWDTH= 2.00E+06 / frequency width in which test was taken (Hz) ENGINEER= 'M. Stennes' / receiver engineer TECH = 'T. Dunbrack' / responsible technician COMMENT low_cal and high_cal indicate selectable calibration levels END
The header keywords describe what part of the receiver was tested, how the test was run, when, and by whom. In the above example, the XL path (RECEPTOR) from beam (FEED) 1 was tested at 175 frequencies using linear (`X') polarization (POLARIZE) with a 20 MHZ bandwidth (BANDWDTH) on June 20th 2001 (TESTDATE) by Mike Stennes (ENGINEER) and Tom Dunbrack (TECH). Also comments by the testing engineer are included.