; PCCOR ;--------------------------------------------------------------- ;! Corrects phases using PCAL tones data from PC table ;# Task UV VLBI CALIBRATION ;----------------------------------------------------------------------- ;; Copyright (C) 1995-1999 ;; Associated Universities, Inc. Washington DC, USA. ;; ;; This program is free software; you can redistribute it and/or ;; modify it under the terms of the GNU General Public License as ;; published by the Free Software Foundation; either version 2 of ;; the License, or (at your option) any later version. ;; ;; This program is distributed in the hope that it will be useful, ;; but WITHOUT ANY WARRANTY; without even the implied warranty of ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the ;; GNU General Public License for more details. ;; ;; You should have received a copy of the GNU General Public ;; License along with this program; if not, write to the Free ;; Software Foundation, Inc., 675 Massachusetts Ave, Cambridge, ;; MA 02139, USA. ;; ;; Correspondence concerning AIPS should be addressed as follows: ;; Internet email: aipsmail@nrao.edu. ;; Postal address: AIPS Project Office ;; National Radio Astronomy Observatory ;; 520 Edgemont Road ;; Charlottesville, VA 22903-2475 USA ;----------------------------------------------------------------------- PCCOR LLLLLLLLLLLLUUUUUUUUUUUU CCCCCCCCCCCCCCCCCCCCCCCCCCCCC PCCOR Corrects phases using PCAL tones data from PC table INNAME Input UV file name (name) INCLASS Input UV file name (class) INSEQ 0.0 9999.0 Input UV file name (seq. #) INDISK 0.0 9.0 Input UV file disk unit # TIMERANG Timerange of a calibrator 1-4 = start day,hr,min,sec 5-8 = end day,hr,min,sec Has to be specified!!! SNVER -1.0 46655.0 Output SN table, 0=>new table INVER -1.0 46655.0 Input PC table, 0=>last one REFANT 0.0 20.0 Ref. antenna, 0=>the first SUBARRAY 0.0 9999.0 Subarray; 0 => all. FREQID Freq. ID to select; 0 => 1. CALSOUR Calibrator source name; blank => any CUTOFF Cable correction: 1 => switch off 0 => switch on BIF 0.0 100.0 Lowest IF number 0=>1 EIF 0.0 100.0 Highest IF number 0=>NIF Use BIF=EIF=0 except for special cases (see help) DELCORR 0.0 1.0 1 => zero MBDELY. Use zero always except for special cases (see help) ---------------------------------------------------------------- PCCOR Type: Task Use: PCCOR corrects for instrumental phase and delay offsets using pulse-calibration data already loaded in the PC table. Adverbs: INNAME.....Input UV file name (name). Standard defaults. INCLASS....Input UV file name (class). Standard defaults. INSEQ......Input UV file name (seq. #). 0 => highest. INDISK.....Disk drive # of input UV file. 0 => any. TIMERANG...Time range of the calibrator to be used. In order: Start day, hour, min. sec, End day, hour, min. sec. Days relative to reference date. SNVER......Desired output SN table. 0 means create a new SN table. INVER......Input PC table. 0 means the last one in the data. REFANT.....Reference antenna, 0 => the first in the antenna list SUBARRAY...The subarray to use. 0 => all FREQID.....Frequency identifier to select (you may determine which is applicable from the OPTYPE='SCAN' listing produced by LISTR). Process each freq. id. separately. CALSOUR....Calibrator source name CUTOFF.....Cable correction: 1 => switch off; 0 => switch on This option was requested by geodesy people. Use zero if you do not have a special idea. BIF........Start IF number to use. 0 => 1 EIF........End IF number to use. 0 => Max available IF in the data Selection of IFs is required if two bands are observed simultaneously. For example X/S observations typically used in astrometry/geodesy. In this case PCCOR should run twice selecting IFs for the each band. The two SN (SN1, SN2) tables will be created with REAL=1, IMAG=0 for unused IFs. CLCAL should be applied twice to combine the two SN table in one CL table. Use the following CLCAL adverbs for the two passes: Pass 1: SNVER=SN1, GAINVER= CL1, GAINUSE=CLTEM, SN1 is PCCOR output SN table of the first IF group. CL1 is input CL table usually with REAL=1 IMAG=0 CLTEM is the output CL table of the first pass. Pass 2: SNVER=SN2, GAINVER= CLTEM, GAINUSE=CLOUT, SN2 is PCCOR output SN table of the second IF group. CLOUT is the output CL table of the both pass. Use BIF=0 EIF=0 in all other cases!! DELCORR......If DELCORR=1, MBDELY is equal zero in the output SN table. table. Multi band delay (MBDELY) of the output CL table will include the sum of the two SN tables MBDELYs. So it does not correspond to the either first IFs or second IFs. If you want to have MBDELY for one of the two IFs, you need to zero MBDELY in the relevant SN table. The zeroing of MBDELY can be done under control of DELCOR. The column MBDELY of a CL table is not used in the calibration procedure but used in the astrometry/geodesy projects to restore the total delay. ----------------------------------------------------------------------- PCCOR: Corrects instrumental phase and delay offsets using pulse-calibration information in the PC table. Documenter: L.R. Kogan RELATED PROGRAMS: FITLD, FRING, PCLOD METHOD Pulse-calibration tones are injected into the VLBA receivers and, in conjunction with the cable calibration system, can be used to measure and track instrumental variations in delay and phase between separate baseband converters. If the pulses are separated by 1 microsecond in time then the corresponding tones are separated by 1 MHz in frequency. The measured phases of the tones allow the connection of the phase across the all IFs. The phase difference between two tones in the same IF allows to estimate the instrumental single-band delay for that IF. The measurement of single band instrumental delay is however subject to ambiguity due to the 2pi*N ambiguity in measured phase. The visibilities of a calibrator are used to resolve this ambiguity. The ambiguity is solved in for each polarization, IF and antenna relative to the reference antenna. The adverbs, TIMERANG, CALSOUR and FREQID select both UV and PC table calibrator data. The phase ambiguity, as measured for the calibrator scan, is used to correct the entire experiment. Each pulse-calibration (PC) table entry is read, corrected for the ambiguity, and an SN table record is written containing single- and multi-band instrumental phase and delay corrections for each IF and polarization. The application of this SN table, using CLCAL, eliminates instrumental phase and delay offsets between individual IF's. Further details of how the pulse-calibration data may be applied are contained in VLBA Scientific Memo. #8, by Craig Walker. COMMENTS Two tones per IF are used by PCCOR to find the instrumental delay. It is not necesarry to have more than two tones per IF for this purpose. If more than two tones exist, the most left and the most right ones are selected. Each FREQID must be processed separately. The selection criteria TIMERANG, FREQID, SUBARRAY are used only for the calibrator during ambiguity solve. Having resolved the ambiguity the task converts each PC table's row to a SN table row. The calibrator has to be observed at all antennas during the selected time range, or some antennas will not be corrected. The calibrator visibilities are averaged (vector) during the time range. The time range of the calibrator scan should be large enough to provide a good SNR but small enough to insure that the fringe rate does not decorrelate the signal. A reasonable compromise is around one minute. If there is no a time interval included all antennas, then some antennas are not corrected. The relevant rows at the SN table has REAL = 1; IMAG = 0. PCCOR can be repeated with another time interval and/or calibrator to provide correction of the antennas which have not been corrected. Use parameters ANTENNA in CLCAL to correct the missing antennas. Some antennas (VLA for example) do not have pulse cals at all. The output SN table does not have a row for such antennas. To avoid the complete loosing of such antennas use CLCAL with OPCODE = 'CALP'. The option 'CALP' is identical to 'CALI' except that uncalibrated data is passed through instead of being discarded.