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 # Data Selection CALSOUR Bandpass calibrator sources. QUAL -10.0 Calibrator qualifier -1=>all CALCODE Calibrator code ' '=>all UVRANGE UV range to select TIMERANG Time range to select STOKES Stokes type to select. SELBAND Bandwidth to select (kHz) SELFREQ Frequency to select (MHz) FREQID Freq. ID to select. BIF 0.0 100.0 Lowest IF number 0=>all EIF 0.0 100.0 Highest IF number 0=>all BCHAN 0.0 2048.0 Lowest channel number 0=>all ECHAN 0.0 2048.0 Highest channel number 0=>all SUBARRAY 0.0 1000.0 Subarray, 0=>all ANTENNAS Antennas to select CLEAN map (optional) IN2NAME Cleaned map name (name) IN2CLASS Cleaned map name (class) IN2SEQ 0.0 9999.0 Cleaned map name (seq. #) IN2DISK 0.0 9.0 Cleaned map disk unit # INVERS -1.0 46655.0 CC file version #. NCOMP # comps to use for model. 1 value per field FLUX Lowest CC component used. NMAPS 0.0 4096.0 No. Clean map files CMETHOD Modeling method: 'DFT','GRID',' ' CMODEL Model type: 'COMP','IMAG' 'SUBI' (see HELP re images) SMODEL Source model, 1=flux,2=x,3=y See HELP SMODEL for details. Control options DOCALIB -1.0 101.0 > 0 calibrate data & weights > 99 do NOT calibrate weights GAINUSE CL (or SN) table to apply DOPOL -1.0 10.0 If >0 correct polarization. PDVER PD table to apply (DOPOL>0) BLVER BL table to apply. FLAGVER Flag table version DOBAND -1.0 10.0 If >0 apply bandpass cal. Method used depends on value of DOBAND (see HELP file). BPVER Bandpass table version SOLINT Solution interval (mins) -1 => do whole time range REFANT Reference antenna OUTVERS BP table version to write SMOOTH Smoothing function. See HELP SMOOTH for details. ANTWT Ant. wts (0 => 1.) BPASSPRM Control information: 1: if > 0 use only the autocorrelation data. 2: print level. 3: If > 0 do not divide data by source model 4: If > 0 store phases only in the BP table. 5: If = 0 divide by 'channel 0' before determining BP. If > 1 switch off the channel 0 divide option. 6: min. amp. closure err 7: min. ph. closure err 8: > 0 => scalar average 10: > 1 => normalize ampl. portion of bandpass by area under BP function. Useful for VLBI. 11: > 1, mode to allow calibration and divide by channel 0. Useful for VLBI. Do not use if you don't understand. See HELP CPARM Fit parameters: 1: No. of terms. 2: Max. no. iterations. 3: Convergence tolerance. 4: Pre-average interval (sec) Default: Auto - 5 min. Cross - 15 min. 5: Fit type (1=Re/Im; 2=A/P) 6: BP table for initial val. 7: Fit phase only (1=> with ampl.; 2=> without) 8: >0 => Autoscale 9: >0 suppress data weighting 10:>0 => save as coefficients rather than normal BP table (no spectral index corr.) ICHANSEL Array of start and stop chan numbers, plus a channel increment and IF to be used to select channels to sum to find a 'channel 0'. If all 0, range set to inner 75 percent of observing band. DOSCALE -1.0 2.0 = -1 -> no spectral index correction - 0, 1 -> fit spectral index = 2 -> fit curvature also SPECINDX Spectral index to correct SPECURVE Spectral index curvature 'Channel 0' uv-data IN3NAME Channel 0 uv name (name) IN3CLASS Channel 0 uv name (class) IN3SEQ 0.0 9999.0 Channel 0 uv name (seq. #) IN3DISK 0.0 9.0 Channel 0 uv disk unit # BADDISK 0.0 9999.0 Disks to avoid for scratch

CPASS Task: This task solves for antenna-based complex polynomial bandpasses. The resulting BP tables are applied using AIPS adverbs DOBAND and BPVER, in the same manner as standard bandpasses determined by BPASS. Solutions can be made for cross-power or auto-correlation bandpasses. In fitting data correlated at the VLBA, the antenna-based fringe rotation applied at the correlator is accounted for in the fit. Model images made with both values of IMAGR's DO3DIMAG option are handled correctly, as are multi-scale images. Set NMAPS = NFIELD * NGAUSS. Fitting of standard bandpasses may require a fair number of terms (CPARM(1)) and may therefore take a long time to compute. CPASS is sometimes used on data that have had the time-averaged bandpass function corrected. It then can use a few terms only with weaker sources to find modest time variable portions of the bandpass shape. Unless you normalize the output bandpass with BPASSPRM(5) and/or BPASSPRM(10), it is important that SETJY or GETJY have been used on the calibrator source in advance. This is particularly true if you choose to use the spectral index parameters. Spectral index parameters are used for "known" sources including 3C286, 3C48, 3C147, 3C138, 3C123, 3C196, and 3C295. They are also fit to the fluxes in the SU table for "unknown" sources. To avoid the use of spectral index, set DOSCALE < 0. 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. CALSOUR....List of sources for which bandpass response functions are to be determined. All ' ' = all sources; a "-" before a source name. means all except ANY source named. If the data file is a single source file no source name need be specified. QUAL.......Only sources with a source qualifier number in the SU table matching QUAL will be used if QUAL is not -1. CALCODE....Calibrators may be selected on the basis of the calibrator code: ' ' => any calibrator code selected '* ' => any non blank code (cal. only) '-CAL' => blank codes only (no calibrators) anything else = calibrator code to select. NB: The CALCODE test is applied in addition to the other tests, i.e. CALSOUR and QUAL, in the selection of sources for which to determine solutions. UVRANGE....Range (min, max) of projected baselines to include 0,0 => all baselines (units: klamda) TIMERANG...Time range of the data to be selected. In order: Start day, hour, min. sec, end day, hour, min. sec. Days relative to ref. date. STOKES.....The desired Stokes type of the output data: 'RR','LL',' '. ' '=>all. SELBAND....Bandwidth of data to be selected. If more than one IF is present SELBAND is the width of the first IF required. Units = kHz, 0=> all SELFREQ....Frequency of data to be selected. If more than one IF is present SELFREQ is the frequency of the first IF required. Units = MHz, 0=> all FREQID.....Frequency identifier to select (you may determine which is applicable from the OPTYPE='SCAN' listing produced by LISTR). If either SELBAND or SELFREQ are set their values overide that of FREQID. However, setting SELBAND and SELFREQ may result in an ambiguity, in which case the task will request that you use FREQID. BIF........First IF to select. 0=>all. EIF........Highest IF to select. 0=>all higher than BIF BCHAN......First channel to use in fit. 0=>all. ECHAN......Highest channel to use in fit. All channels are read in and the solution applies to all channels. The outermost channels may be excluded from the fitting process in this way. SUBARRAY...Subarray number to select. 0=>all. ANTENNAS...A list of the antennas for which bandpasses are to be determined.. If any number is negative then all antennas listed are NOT to be used and all others are. The following specify a CLEAN model to be used if a single source was specified in SOURCES: IN2NAME....Cleaned map name (name). Standard defaults. Note: a CLEAN image for only a single-source may be given although it may be in a multi-source file. If the source table contains a flux, then that flux will be used to scale the components model to obtain the stated total flux. This is needed since initial Cleans may not obtain the full flux even though they represent all the essentials of the source structure. IN2CLASS...Cleaned map name (class). Standard defaults. IN2SEQ.....Cleaned map name (seq. #). 0 -> highest. IN2DISK....Disk drive # of cleaned map. 0 => any. INVERS.....CC file version #. 0=> highest numbered version NCOMP......Number of Clean components to use for the model, one value per field. If all values are zero, then all components in all fields are used. If any value is not zero, then abs(NCOMP(i)) (or fewer depending on FLUX and negativity) components are used for field i, even if NCOMP(i) is zero. If any of the NCOMP is less than 0, then components are only used in each field i up to abs(NCOMP(i)), FLUX, or the first negative whichever comes first. If abs(NCOMP(i)) is greater than the number of components in field i, the actual number is used. For example NCOMP = -1,0 says to use one component from field one unless it is negative or < FLUX and no components from any other field. This would usually not be desirable. NCOMP = -1000000 says to use all components from each field up to the first negative in that field. NCOMP = -200 100 23 0 300 5 says to use no more than 200 components from field 1, 100 from field 2, 23 from field 3, 300 from field 5, 5 from field 6 and none from any other field. Fewer are used if a negative is encountered or the components go below FLUX. FLUX.......Only components > FLUX in absolute value are used in the model. NMAPS......Number of image files to use for model. For multi-scale models, set NMAPS = NFIELD * NGAUSS to include the Clean components of the extended resolutions. If more than one file is to be used, the NAME, CLASS, DISK and SEQ of the subsequent image files will be the same as the first file except that the LAST 3 or 4 characters of the CLASS will be an increasing sequence above that in IN2CLASS. Thus, if INCLASS='ICL005', classes 'ICL005' through 'ICLnnn' or 'ICnnnn', where nnn = 5 + NMAPS - 1 will be used. Old names (in which the 4'th character is not a number) are also supported: the last two characters are '01' through 'E7' for fields 2 through 512. In old names, the highest field number allowed is 512; in new names it is 4096. CMETHOD....This determines the method used to compute the model visibility values. 'DFT' uses the direct Fourier transform, this method is the most accurate. 'GRID' does a gridded-FFT interpolation model computation. ' ' allows the program to use the fastest method. NOTE: when using a model derived from data with different uv sampling it is best to use 'DFT' CMODEL.....This indicates the type of input model; 'COMP' means that the input model consists of Clean components, 'IMAG' indicates that the input model consists of images. 'SUBI' means that the model consists of a sub-image of the original IMAGR output. If CMODEL is ' ' Clean components will be used if present and the image if not. SUBI should work for sub-images made with DO3DIM true and sib-images of the central facet made with DO3DIM false, but probably will not work well for shifted facets with DO3DIM false. Use BLANK rather than SUBIM in such cases. CALIB will set a scaling factor to correct image units from JY/BEAM to JY/PIXEL for image models. If the source table contains a flux, then that flux will be used to scale the components model to obtain the stated total flux. This is needed since initial Cleans may not obtain the full flux even though they represent all the essentials of the source structure. SMODEL.....A single component model to be used instead of a CLEAN components model; if abs (SMODEL) > 0 then use of this model is requested. SMODEL(1) = flux density (Jy) SMODEL(2) = X offset in sky (arcsec) SMODEL(3) = Y offset in sky (arcsec) SMODEL(4) = Model type: 0 => point model 1 => elliptical Gaussian and SMODEL(5) = major axis size (arcsec) SMODEL(6) = minor axis size (arcsec) SMODEL(7) = P. A. of major axis (degrees) 2 => uniform sphere and SMODEL(5) = radius (arcsec) DOCALIB....If true (>0), calibrate the data using information in the specified Cal (CL) table for multi-source or SN table for single-source data. Also calibrate the weights unless DOCALIB > 99 (use this for old non-physical weights). The calibration is applied prior to the bandpass determination. GAINUSE....version number of the CL table to apply to multisource files or the SN table for single source files. 0 => highest. DOPOL......If > 0 then correct data for instrumental polarization as represented in the AN or PD table. This correction is only useful if PCAL has been run or feed polarization parameters have been otherwise obtained. See HELP DOPOL for available correction modes: 1 is normal, 2 and 3 are for VLBI. 1-3 use a PD table if available; 6, 7, 8 are the same but use the AN (continuum solution) even if a PD table is present. PDVER......PD table to apply if PCAL was run with SPECTRAL true and 0 < DOPOL < 6. <= 0 => highest. BLVER......Version number of the baseline based calibration (BL) table to appply. <0 => apply no BL table, 0 => highest. FLAGVER....specifies the version of the flagging table to be applied. 0 => highest numbered table. <0 => no flagging to be applied. DOBAND.....If true (>0) then correct the data for the shape of the antenna bandpasses using the BP table specified by BPVER. The correction has five modes: (a) if DOBAND=1 all entries for an antenna in the table are averaged together before correcting the data. (b) if DOBAND=2 the entry nearest in time (including solution weights) is used to correct the data. (c) if DOBAND=3 the table entries are interpolated in time (using solution weights) and the data are then corrected. (d) if DOBAND=4 the entry nearest in time (ignoring solution weights) is used to correct the data. (e) if DOBAND=5 the table entries are interpolated in time (ignoring solution weights) and the data are then corrected. BPVER......Specifies the version of the BP table to be applied. <0 => no bandpass correction done. ** NOTE - AIPS does not now have a way to "concatanate" ** BP tables. Thus, if one determines a BP table having ** applied a BP table, one has no way to get that net ** calibration applied to the data. Nonetheless, it may ** be of interest, for example, to use DOBAND=1 for ** example and then to see what is left as a ** time-variable BP, examining it with BPLOT. SOLINT.....the interval over which to average the data before solving for the bandpasses (MINS). (0 => scan, -1 => whole timerange) REFANT.....the antenna to use as a reference in the least squares solution. OUTVERS....the version of the BP table to fill. (0 => 1) SMOOTH.....Specifies the type of spectral smoothing to be applied to a uv database . The default is not to apply any smoothing. The elements of SMOOTH are as follows: SMOOTH(1) = type of smoothing to apply: 0 => no smoothing To smooth before applying bandpass calibration 1 => Hanning, 2 => Gaussian, 3 => Boxcar, 4 => Sinc To smooth after applying bandpass calibration 5 => Hanning, 6 => Gaussian, 7 => Boxcar, 8 => Sinc SMOOTH(2) = the "diameter" of the function, i.e. width between first nulls of Hanning triangle and sinc function, FWHM of Gaussian, width of Boxcar. Defaults (if < 0.1) are 4, 2, 2 and 3 channels for SMOOTH(1) = 1 - 4 and 5 - 8, resp. SMOOTH(3) = the diameter over which the convolving function has value - in channels. Defaults: 1,3,1,4 times SMOOTH(2) used when input SMOOTH(3) < net SMOOTH(2). Note that any use of SMOOTH in CPASS will require that the same SMOOTH values be used when accessing any data to be calibrated by the BP table produced by CPASS. ANTWT......Antenna weights for up to 30 antennas. (0=>1.0) BPASSPRM...Control information: (1) > 0 => fill BP table with autocorrelation data only, ignoring the phases. (2) print level (3) > 0 => do not divide data by a model of the source. The default is that the data will be divided by a source model, the model used will be (in order of decreasing priority): (1) the flux density specified in the SU table (2) a point source model (SMODEL) (3) CLEAN components, If BPASSPRM(5) = 0 the data will not be divided by a source model. (4) > 0 => store only the phase of the complex bandpass function in the BP table. You may want to do this if, for instance, your data have been normalized by the autocorrelation data as is possible at the VLA. (5) = 0 => divide the line data by 'channel 0', this is a useful operation if you wish to determine your antenna based bandpasses from uncalibrated data. Channel 0 is a 'VLAism' for the vector averaged center 75 percent of the observing band. If IN3NAME is specified CPASS will use an external channel 0, else it will generate one internally. Note that this is on a record by record basis and, if you have good phase stability, it might be better to do the normalization on the SOLINT average instead; see CPARM(8). (6) If > 0, then the values of any amplitude closure errors whose abs. percentage value exceeds BPASSPRM(6) will be printed. (7) If > 0, then the values of any phase closure errors whose value exceeds BPASSPRM(7) degrees will be printed. (8) If > 0, then the amplitudes will be scalar averaged before determining the solutions. (10) If > 0 then will normalize the amplitude portion of the bandpass function by the area under the curve (to force the area to = 1.0). This is useful for VLBI data where a useful 'channel 0' is sometimes difficult to obtain. (11) If > 0 will then allow the user to apply calibration and divide by channel 0. This is disallowed in normal useage, however VLBI users need this because they need to apply delay and fringe rate solutions to the data before dividing by channel 0 (delay is especially important). CPARM..... Parameters relevant to the least-squares fit: (1) No. of terms to use in the polynomial expansion. 0 -> 20 (2) Maximum number of iterations allowed. 0 -> 50 (3) Convergence limit. 0 -> 0.001 ***Convergence is a real issue, you may need to set CPARM(2) and CPARM(3) fairly high.*********** Failure to converge will be reported but the solution will be saved anyway. (4) Pre-average interval (seconds). CPASS pre-averages the uv-data over sub-intervals of each solution interval to improve the SNR before the bandpass fit. For VLBA data the pre-average interval should not be very long compared to the time-scale over which the fringe-rate is changing significantly at each antenna. For low-SNR VLBA data, however, it is more important to pre-average over a longer interval when solving for cross-power bandpass solutions. For VLA data the pre-average interval can be set to a large value so that the entire solution interval is averaged before the fit. Default: Autocorrelation bandpass - 5 min. Cross-correlation bandpass - 15 min. The data are not averaged beyond scan boundaries no matter what the pre-averaging value is. (5) Fit type: 0 -> 2 1: Chebyshev expansion of (Re, Im). 2: Chebyshev expansion of (Amp, Phs). (6) BP table to use for initial estimates of the polynomial coefficients. Must be of compatible type to the present fit. (7) Fit phase only ? (1 => fit for phase only using initial amplitude solutions; 2 => fit for phase without reference to amplitude data. (8) If >= 0 then auto-scale the data before the fit to unit amplitude and zero mean phase. See also BPASSPRM(5). With data of good phase stability, the scan average will produce a much less noisy normalization than the record-by-record divide by channel 0. ***** You must use one (or both) of these normalizations; the fitting routine in CPASS does not work on un-normalized data. ***** (9) The fitting is done using data weights. If CPARM(9) <= 0, the pre-average is used to find an rms for each baseline and channel and the data weight is set based on this rms tempered some by the input weight. If CPARM(9) > 0, the pre-average rms is ignored. If CPARM(9) > 1.5, the data weights are set to one everywhere (except flagged data of course). (10) > 0 => Save the results as the Chebyshev polynomial coefficients, otherwise convert to a normal Real/imaginary BP table. When applying BP tables with interpolations, whatever is stored in the BP table is interpolated. This option allows you to interpolate coefficients rather than bandpasses. ICHANSEL.. Array of start, stop, and increment channel numbers plus an IF used for channel selection in the averaging to compute a channel 0. Up to 20 sets if channels/IF may be entered. The first having ICHANSEL(2,i) <= 0 terminates the list. ICHANSEL(4,i) is the IF number, with <= 0 meaning all IFs. If an IF has no ICHANSEL set for it, then the inner 75 percent of that IF is used. Note that these are absolute channel numbers; they are not relative to BCHAN. DOSCALE....Controls whether spectral index corrections are made. DOSCALE < 0 => do no spectral index correction. DOSCALE >= 0 => do spectral index correction, using SPECINDX and SPECURVE for the first calibrator or using known parameters, or fitting fluxes in the SU table. DOSCALE >= 2 => fit spectral index and curvature for unknown sources. Do this only for well-determined fluxes over a wide frequency range. SPECINDX...The fit bandpasses are corrected for a calibrator spectral index. The calibrator flux is assumed to be frequency^SPECINDX so the bandpass is multiplied by (freq/f0) ** SPECINDX when SPECINDX is not zero. If SPECINDX = 0 and the calibrator source is one of 3C286, 3C48, 3C147, 3C138, 3C123, 3C196, or 3C295 (the standard "known" ones) SPECINDX and SPECURVE will be set to the known (Perley 20xx) values from SETJY. If SPECINDX=0 and the source is not one of the known ones, then a spectral index (with curvature if DOSCALE=2) is fit to the fluxes in the source table. SPECURVE...If SPECINDX is not zero, a curvature term may be added to the above correction as A = log(f/f0) * SPECINDX + log(f/f0)^2 * SPECURVE(1) + log(f/f0)^3 * SPECURV(2) + log(f/f0)^3 * SPECURV(2) and then multiply by 10^(-A/2.) where the 2 is because the BP tables are voltages rather than powers. f0 is taken to be 1.0 GHz by convention and all logs are base 10.0. The following specify a uv-file which can be used as an external 'channel 0'. If all the IN3* adverbs are blank, then the task will determine channel 0 from the line data itself, unless BPASSPRM(5) = 1, in which case no channel 0 division will be done. IN3NAME....Channel 0 uv name (name). Standard defaults. IN3CLASS...Channel 0 uv name (class). Standard defaults. IN3SEQ.....Channel 0 uv name (seq. #). 0 -> highest. IN3DISK....Disk drive # of Channel 0 uv 0 => any. BADDISK....A list of disks on which scratch files are not to be placed. This will not affect the output file.

CPASS: Task to determine the instrumental bandpass response Documentor: A. J. Kemball Related Programs: BPASS, CALIB, POSSM, LISTR, SPLIT, TVFLG OVERVIEW This purpose of this task is to determine the antenna-based instrumental bandpass response, modeled as a complex polynomial expansion, using either autocorrelation or cross-correlation calibrator data. This task is closely related in function to BPASS, which in contrast determines the bandpass response on a channel by channel basis. CPASS offers an alternative bandpass calibration method which may be useful in some cases. In fitting the polynomial bandpass response function, CPASS correctly models the antenna-based fringe rotation applied to both autocorrelation and cross-correlation data by the VLBA correlator, and is therefore useful for determining bandpass solutions for high-frequency VLBA data. It has also proved useful in deriving bandpass solutions for narrow-band VLBA data. MODES OF OPERATION CPASS has two major modes of operation: i) AUTOCORRELATION BANDPASSES In this mode CPASS uses only the autocorrelation data in determining the bandpass response function for each antenna. The phase response of the resulting solutions is zero. This mode is selected by setting BPASSPRM(1) = 1. ii) CROSS-CORRELATION BANDPASSES In this mode CPASS factorises the baseline-based cross-power data on the specified continuum calibrator sources into antenna-based complex bandpass response functions using a non-linear least squares method. This is analogous to self-calibration except the solution at each antenna is a parametrized bandpass response. The phase response of the reference antenna is zero in this case and this mode is selected by setting BPASSPRM(1) = 0. In solving for cross- power bandpasses a phase-only solution may be performed with an existing AC bandpass solution used to fix the amplitude response. GENERAL CONSIDERATIONS The effect of calibrator source resolution can be minimized by dividing the uv-data by a pre-determined source model or by the so-called "channel-zero". These options are selected using BPASSPRM(3) and BPASSPRM(5) respectively. The polynomial bandpass solutions are written to the standard BP tables used by BPASS and are applied using adverb DOBAND in the standard manner. Multiple solutions can be appended to the same BP table by running CPASS several times with the same output BP table specified by OUTVERS. The uv-data can be selected, calibrated, edited and smoothed prior to the bandpass solutions using the standard AIPS adverbs for this purpose (i.e. DOCALIB, GAINUSE, FLAGVER, BIF, EIF, SMOOTH etc.). Comments on some specific adverbs follow: SOLINT: SOLINT defines the time interval to use in determining each bandpass solution. The default (SOLINT = 0) determines a bandpass solution for each scan defined in the NX table. Setting SOLINT = -1 will determine only one bandpass solution for each antenna for the entire run. REFANT: REFANT defines the antenna to be used as the reference in the least squares solution. A useful choice is an antenna with good SNR, at the center of the array that was present for a significant fraction of the observing run. OUTVERS: The version of the BP table to fill. The default (OUTVERS = 0) will cause a new table to be generated. Solutions can be appended to an existing BP table but BPASS and CPASS solutions cannot be stored in the same table. SMOOTH: Specifies the type of spectral smoothing that can be applied to the data before the bandpasses are determined. See HELP SMOOTH for more details. ** WARNING ** If SMOOTH is specified then all channels of the database must be present in a single file, it will not work properly if for instance you have split your data into 4 files each of 16 channels. The rest of CPASS will work with no problem in that mode but the SMOOTH option will result in corrupted data. See the HELP section for a full description of the BPASSPRM parameters. PARAMETERS CONTROLLING THE LEAST SQUARES FIT The least squares fit is controlled using parameters specified in adverb CPARM. This task uses a NETLIB routine by S.G. Nash (Siam J. Numer. Anal. 21 (1984) which uses a truncated Newton algorithm. CPASS can be somewhat slow when solving for a large number of free parameters. The convergence can be monitoring by setting the print level using BPASSPRM(2)=1, and CPASS re-started with different least squares parameters to improve this if necessary. A description of the least squares parameters is given below: CPARM(1)...Number of terms to use in the polynomial expansion for the bandpass response function at each antenna. Reasonable values to use here are in the range 10-30. This number cannot exceed the number of frequency channels in each IF. Default: 20 CPARM(2)...Maximum number of iterations allowed. The least squares solution will terminate after this number of function evaluations. Default: 50 CPARM(3)...Convergence limit. This is the fractional convergence tolerance. Default: 0.001 CPARM(4)...Pre-average interval (seconds). CPASS pre-averages the uv-data over sub-intervals of each solution interval to improve the SNR before the bandpass fit. For VLBA data the pre-average interval should not be very long compared to the time-scale over which the fringe-rate is changing significantly at each antenna. For low-SNR VLBA data, however, it is more important to pre-average over a longer interval when solving for cross-power bandpass solutions. For VLA data the pre-average interval can be set to a large value so that the entire solution interval is averaged before the fit. Default: Autocorrelation bandpass - 5 min. Cross-correlation bandpass - 15 min. CPARM(5)...Fit type. The task can solve for bandpass functions where either (Re,Im) or (Amp,Phs) are each expanded separately as Chebyshev series. The (Amp,Phs) solution is recommended, and the former may only be necessary if residual delays have not been removed before the bandpass fit. Default: 2 (amplitude and phase). CPARM(6)...In solving for a cross-power bandpass, a pre-existing AC bandpass solution can be used either as a starting point for the fit or to fix the amplitude response of the bandpass solution. This BP table must have been fit using the same fit type (CPARM(5)) as is presently being used. Again, A&P is recommended. Default: 0 (do not read a BP table for initial values) CPARM(7)...This parameter determines whether phase alone is fitted. CPARM(7) = 1 will fit for phase only using the amplitude response specified in CPARM(6). CPARM(7) = 2 will fit for phase alone without reference to the amplitude response. Default: 0 CPARM(8)...Auto-normalization. This parameter enables auto-scaling of the data to unit mean amplitude and zero mean phase after each pre-average interval. This is necessary to correct for calibrator resolution not previously removed. Default: 1 (auto-scaling enabled). CPARM(10) Option to save coefficients in the BP table (used to be the only choice). > 0 save coefficients, <= 0 save an evaluated real and imaginary bandpass of the "normal" sort. All calibration routines plus POSSM can handle either. The time smoothing and averaging is done over whatever numbers are in the BP table, and it is more intuitive to average normal bandpasses rather than Chebyshev polynomials. These parameters will be consolidated and revised as further experience is gained with the algorithm.