As of Tue Jan 16 10:02:53 2018

DFCOR: Task applies differential corrections to CL 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 #
SOURCES                            Source list ' '=>all.
CALSOUR                            Reference source list.
                                   Only one is allowed
STOKES                             Stokes type to process
SELBAND                            Bandwidth to select (kHz)
SELFREQ                            Frequency to select (MHz)
FREQID                             Freq. ID to select, 0=>all
BIF               0.0      100.0   Lowest IF number 0=>all
EIF               0.0      100.0   Highest IF number 0=>all
TIMERANG                           Time range to use.
ANTENNAS                           Antennas to correct.
SUBARRAY          0.0     9999.0   Subarray;  0 => 1.
GAINVER                            Input CL table 0=>high
GAINUSE                            Output CL table: not =
                                   GAINVER -> high+1
OPCODE                             Operation code.
CLCORPRM                           Parameters (see HELP DFCOR).
BADDISK           0.0     9999.0   Disks to aviod for scratch
CALIN                              Input file with the list of
                                   antennas, times and relevant
                                   atmosphere vertical delay.
                                   Used only with OPCODE='ATMO'


Task:  This task makes a differential  corrections to a CL table.
  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.
  SOURCES....list of sources to process.
             '*' = all; a "-" before a source name
             means all except ANY source named.
  CALSOUR....Reference source list. Only one is allowed
  STOKES.....The desired Stokes to correct.
             'R', 'L', 'I', '  '=> all available
  FREQID.....Frequency identifier to select (you may determine
	     which is applicable from the OPTYPE='SCAN' listing
	     produced by LISTR).
  BIF........First IF to process. 0=>all.
  EIF........Highest IF to process. 0=>all higher than BIF
  TIMERANG...Time range of the data to be used. In order:
             Start day, hour, min. sec,
             end day, hour, min. sec. Days relative to ref.
  ANTENNAS...A list of the antennas to be modified.  If any
             number is negative then all antennas listed  are
             NOT to be modified.  All 0 => use all.
  SUBARRAY...The subarray to modify. Do only one at a time.
  GAINVER....Input CL table version. If GAINVER is equal zero or
             greater than the total number of the CL tables
             then GAINVER is equal to the last existing CL table.
  GAINUSE....Output CL table version.  If GAINUSE not equal GAINVER
             (after GAINVER default applied), then a new CL table is
             created and the input CL table version (GAINVER) is
             copied to version=(high+1).  This adverb allows you to
             correct a CL table in place or to create a new one, but
             not to overwrite an existing one other than the input.
  OPCODE.....Operation code (see also EXPLAIN DFCOR)
             Right now only optype 'ATMO' works at the differential
             'POLR' => Modify Right-Left phase difference using
                       phases in CLCORPRM (deg); up to 20 IFs
                       may be processed at a time.  Note that
                       with 'POLR' the antenna table is also
                       modifed.  'POLR' should only be used once.
             'PHAS' => Rotate phase of residual gain by
                       CLCORPRM (deg); up to 20 IFs may be
                       processed at a time
             'RATE' => Rotate phase of residual gain versus time.
                       CLCORPRM(1) degrees constant term.
                       CLCORPRM(2) = rate of change of phase
                       CLCORPRM(3) - (6) = day, hr, min, sec at
                         which the "zero" phase (CLCORPRM(1)) is
             'OPAC' => apply atmospheric opacity amplitude
                       corrections using zenith opacity of
                       CLCORPRM(1) nepers.
             'ADEL' => Correct phases, delays and rates for
                       neutral atmospheric delay.
                       CLCORPRM(1) = total pressure (mbars) at
                         station, NOT at sea level.
                       CLCORPRM(2) = partial pressure of water.
                       CLCORPRM(3) = Temperature (C)
                       CLCORPRM(4) = Tropospheric lapse rate
                                  (K/km) (should be negative)
                       CLCORPRM(5) = Height of tropopause (km)
                       CLCORPRM(6) = Scale height of water
                                  vapor (km).
             'GAIN' => Correct using polynominal gain curve for
                       antenna gain as a function of the zenith
                       angle (ZA) in degrees.
                       correction = CLCORPRM(1) +
                          ZA * CLCORPRM(2) +
                          ZA * ZA * CLCORPRM(3) ...
             'CLOC' => Correct residual delay and model parms
                       for the effects of a linear clock drift
                       at a particular antenna.
                       CLCORPRM(1) = rate of change of station
                         clock (nanosec/day)
                       CLCORPRM(2) = clock value at the "zero"
                         time specified by CLCORPRM(3)-(6)
                       CLCORPRM(3) - (6) = day, hr, min, sec at
                         which the "zero" clock (CLCORPRM(2)) is
                       CLCORPRM(7) : correction has three modes,
                         if = 0 then the clock drift is added
                         as a small correction and CLCORPRM(2)
                         is ignored.
                         if = 1 then the total correction set
                         by the CLCORPRMS is added.
                         if = 2 then the values present in the
                         CL table are replaced by those defined
                         by CLCORPRM(1)-CLCORPRM(6).
             'PANG' => Add or remove parallactic angle
                       corrections from CL table entries.
                       CLCORPRM(1) > 0 => Add corrections
                       CLCORPRM(1) =< 0 => Remove corrections
             'PONT' => Correct for predictable pointing offset
                       of an antenna. CLCORPRM(1) is the linear
                       rate of change of antenna gain as the
                       pointing drifts.
             'IONS' => Make ionispheric Faraday rotation
                       corrections using one of several models.
                       CLCORPRM(1) = Model type:
                       1 = Chiu model, CLCORPRM(3) = Sunspot no.
             'ANTP' => Correct antenna and/or source position;
                       antenna / source corrections are values to be
                       added to the old positions in meters / sec of arc.
                       The antenna (only one) must be specifyed in
                       the case of antenna correction.
                       The source (only one) must be specified in
                       the case of source correction.

                       !!!!!!!!!!!!!!!!!!! ATTENTION !!!!!!!!!!!!!!!!!!
                       Starting June 2001 DFCOR corrects the AN or/and
                       the SU table, if the relevant correction of the
                       antenna or/and the source is carried out.
                       So the application of the corrected CL table is
                       required to match the data.
                       Once DFCOR has been run, then the CL table must
                       not be deleted and the correction can be undone
                       only by doing it again with opposite sign.
                       If you might forget applying this, then use the
                       task SPLAT to apply it immediately.

                       1 = "X" correction in meters.
                       2 = "Y" correction in meters.
                       3 = "Z" correction in meters.
                       4   no longer used
                       5 = Correction in the picture plane towards
                           the RA direction in sec of arc.
                           So it is RA correction, muliplied
                           by COS(DECL).
                       6 = Declination correction in sec of arc
                       7   no longer used
             'PCAL' => MkIII manual phase cal; replace the gain
                       correction in the CL table with unit
                       vectors with phases given in CLCORPRM.
                       CLCORPRM(1) corresponds to BIF etc.
                       Phases are given in degrees.
             'PCFX' => Patch up missing phase cals.  CLCORPRM
                       gives the expected relationship between
                       phase cals and uses any non blanked
             'SBDL' => Add a delay to the IF residual delays.
                       Values given in CLCORPRM correspond to
                       IFs BIF, BIF+1,... EIF in nanosec.
	     'MBDL' => Change the multiple band delay by
		       introducing the corresponded slope at
		       phase vs IF frequency dependence.
		       Values given in CLCORPRM correspond to
                       IFs BIF, BIF+1,... EIF in nanosec		
             'SSLO' => Correct the phase only for an incorrect
                       frequency used to calculate the phase
                       at the VLA.  CLCORPRM(1) gives the
                       frequency error in MHz.
             'ANAX' => Correct the delay, rate and phase for
	               antenna axis offset.
		       CLCORPRM is an array of axis offsets in
		       meters corresponding to the antenna list
                       given. Note that with 'ANAX' the antenna
                       table is also modifed.
             'ATMO' => apply atmospheric delay corrections using
                       zenith delay for the antennas and times given
                       in the input file. The values of zenith delay
                       should correspond to the desired correction.
                       The corrections for the interferometer delay
                       and phase are added (with sign) to the relevant
                       columns of the CL table, which in turn are
                       added to the data when calibration is applied.
                       Example 1. The correlator did not provide any
                                  atmosphere correction.  Since, the
                                  the atmospheric delays are positive,
                                  the corrections entered in the
                                  CALIN should be negative.
                       Example 2. The correlator model used 210 cm
                                  for the zenith delay.  The true
                                  zenith delay was 220cm.  Thus,
                                  DFCOR has to make additional
                                  additive correction of -10cm, and
                                  the CALIN entry should -10cm.

                       If CALSOUR.NE.'' then

                       DFCOR reads the CL table twice.

                       First time the data corresponded to the given
                       calibrator (CALSOUR(1))
                       are read and the relevant delays and rate of
                       delays recalculated from the input file of zenith
                       delays. The found delays and rate of delays
                       are stored at the array together with the arrays
                       of time and antennas.

                       Second time the data corresponded to the given
                       source list (SOURCE) are read and the relevant
                       delays and rates of delay are calculated from the
                       input file of zenith delays. Then the stored delays
                       and rates of delay for the calibrator are
                       interpolated to the time of the CL table row and
                       the interpolated values are subtracted of the
                       calculated source delays and rate of delays.
                       The differences are recorded to the CL table

  CLCORPRM...Parameters: see above.
  BADDISK....A list of disks on which scratch files are not to
             be placed.  This will not affect the output file.
  CALIN......Input file (used at OPCODE = 'ATMO')
             The first (ascii) data record should specify NLINES,
             the number of the lines at the file.
             Then, NLINES records must follow, each with three numbers:
                   The station number;
                   The time in dd hh mm ss; for example 01 13 26 35.3
                   The zenith delay error in cm;
                   The values given at the zenith delay error correspond
                   to the desired correction.
                   Therefore the given zenith delay error should be
                   subtructed from the full zenith delay.
                   The example of a line:  2 01 13 26 35.3  5.3
                   The line is for antenna 2; The time corrersponds
                   to day=1; 13hours; 26 min; 35.3sec;
                   The delay at zenith is 5.3cm


DFCOR:  Task to apply corrections to a CL table corresponding to the
difference of the source (SOURCE) and the reference source (CALSOUR(1))
Documentor: L.R. Kogan

This task will compute various corrections and apply them
directly to a calibration (CL) table.  The operation to be done
is determined by OPCODE.  Details and/or additional information
for the various models is given below.

     This option causes corrections to be made to remove the
systematic phase offset between the right and left hand
polarization systems.  The phase offsets are passed in CLCORPRM
in degrees and are typically determined from running LISTR on
polarization calibrated data on a source with known polarization
angle.  Up to 10 IFs specified by BIF and EIF may be processed
in a single run with the corresponding phase values in
CLCORPRM(1) - CLCORPRM(10).  Specified phase corrections are
made to the left hand polarization.
     Because the feed polarization parameters must be modified
as well as the Calibration table this option will cause the AN
table corresponding to the specified subarray to be modified as
well as the specified CL table.
     NB: the modification of both the CL and AN table are
cumulative so a given correction should be made only once.
Thus, if multiple CL tables in the same subarray are to be
corrected OPCODE='PHAS' with STOKES='L' should be used for each
IF separately for CL tables after the first run with
OPCODE='POLR'.  (If the AN table gets messed up, correct all
relevant CL tables and then rerun PCAL; further runs of CLCOR to
correct the R-L phase difference will be unnecessary.)

     This causes the specified phases to be rotated by
CLCORPRM(I) degrees.

     This causes the specified amplitudes to be corrected for
atmospheric opacity using a zenith opacity of CLCORPRM(1)
nepers.  This operation does not modify the total model values.
Exact values of the zenith opacity depend on the weather,
especially at higher frequencies, but typical values are given
in the following:
     327 Mhz  0.007
     610 Mhz  0.007
     1.4 GHz  0.008
     2.3 GHz  0.01
     5.0 GHz  0.01
     8.4 GHz  0.01
     10  GHz  0.012
     15  GHz  0.02
     22  GHz  0.05
     40  Ghz and up are highly dependent on the weather.

     This causes the phases, delays and rates to be corrected
for a model atmosphere.  The model used is a two term round
earth approximation.  The parameters passed are CLCORPRM(1) the
total atmospheric pressure in millibars at the station, NOT
refered to sea level and CLCORPRM(2), the partial pressure of
water vapor in millibars.
     Pressure in mm. of Hg. can be converted to millibars by
multiplying by 1.33322.
     Measurments of Dew point can be converted to relative
humidity using the following table:

         Relative Humidity ( percent) from temp and DP.

DP depression               Dew Point deg C
 temp-DP deg C    -10       0      10      20      30

      0            100     100     100     100     100
      1             92      93      94      94      94
      2             86      87      88      88      89
      3             79      81      82      83      84
      4             73      75      77      78      80
      5             68      70      72      74      75
      6             63      66      68      70      71
      7             59      61      63      66      68
      8             54      57      60      62      64
      9             51      53      56      58      61
     10             47      50      53      55      57
     12             41      44      47      49
     14             35      38      41      44
     16             31      34      37      39
     18             27      30      33      35
     20             24      26      29      32
     22             21      23      26
     24             18      21      23
     26             16      18      21
     28             14      16      19
     30             12      14      17

     The partial pressure of water vapor is obtained by
multiplying the relative humidity (as a fraction) times the
vapor pressure of water obtained from the following table:

     Temp (C)   Pressure(mbars)   Temp (C)   Pressure(mbars)
     --------  ----------------   ---------  ---------------
      -40           1.29
      -30           3.81             -25         6.35
      -20          10.35             -15        16.55
      -10          26.00              -5        40.17
        0          61.05               5        87.23
       10         122.78              15       170.36
       20         233.78              25       316.72
       30         424.28              35       562.29
       40         737.59
   Information from Handbook of Physics and Chemistry published
by The Chemical Rubber Co. 46th ed.

     The tropospheric lapse rate is the rate at which the
atmosphere cools with increasing height.  The model used assumes
that the temperature declines linearly to the tropopause and
then is constant.  Accurate values can be derived from
radiosonde data or approximate values can be obtained from the
following table.  An accurate value of the height of the
tropopause may be derived from radiosonde data; typical values
can be obtained from the following table (Davis et al. 1985,
Radio Science 20, 1593):

      Latitude     Lapse rate (K/km)    Height of tropopause(km)
         30 N         -4.7 to -5.9                 16
         45 N             -6.5                     11.2
         60 N             -3.9                      8

     The scale height of the water vapor may be determined from
radiosonde data (default = 2.2 km).

     This causes the specified amplitudes to be corrected by a
factor determined from a polynomial gain curve as a function of
zenith angle (in degrees).  The coefficients are specified by
CLCORPRM and up to 20 terms are allowed. This allows for
correction of amplitudes for the zenith angle (i.e. elevation)
dependent behavior of the antenna gain.
     The amplitudes are modified by:
                 ZA*ZA*CLCORPRM(3) ...

     This causes the residual delays and model values to be
corrected for a linear clock drift at a particular antenna. The
parameters needed are :
     1)   clock rate (nanosec/day) ...... CLCORPRM(1)
     2)   "zero" clock (nanosec) ........ CLCORPRM(2)
     3)   time of "zero" clock
            measurement          ........ CLCORPRM(3) -
     4)   correction mode        ........ CLCORPRM(7)
               if = 0 then the clock drift is added
               as a small correction and CLCORPRM(2) is
               if = 1 then the total correction set
               by the CLCORPRMS is added.
               if = 2 then the values present in the
               CL table are replaced by those defined
               by CLCORPRM(1)-CLCORPRM(6).
          Mode = 2 gives the user the opportunity to set the
          residual delay manually.


    This option add or removes the phase of the parallactic
angle to/from the residual phases of the specified CL table
entries.  The AIPS polarization calibration routines expect
that this correction has NOT been made to the raw data; if the
parallactic angle corrections has been applied, then this
option with CLCORPRM(1) .le. 0 will remove it.  The parallactic
angle correction may be added using CLCORPRM(1) .gt. 0.
    Note: the above definitions of applying or removing the
parallactic angle correction assumes that the phase of the
first polarization (RCP for VLA, VLBA) decreases with
increasing parallactic angle.  This involves the definition of
RCP.  If the opposite definition of RCP and LCP is used, then
the sense of applying or removing the parallactic angle
correction given above is removed.

     This causes the specified amplitudes to be corrected for
any gross predictable pointing error. The antenna gain
correction factor is specified by a time at which the pointing
was set correctly (i.e. the antenna gain is correct) and a
linear drift factor. The TIMERANG parameters define the time at
 which pointing was done, CLCORPRM(1) specifies the rate of
change of antenna gain (per hour). The inverse of this will be
applied to the CL gain entries in order to correct the amplitude

     This option causes ionispheric Faraday rotation
corrections to be computed and applied to the CL table.
Several methods are available for determining the Faraday
rotation correction; the method selected is indicated by the
values given in CLCORPRM.
     The group and phase delays introduced by the ionospheric
plasma are also computed and applied to the CL table.

     CLCORPRM(1):  Electron density model type:

CLCORPRM(1) = 1 => Chiu model.

     The electron column density will be computed using a Chiu
model using software provided by Chris Flatters.  The model is
described in Chiu, 1975, J. At. Terr Phys. 37, 1563).
CLCORPRM(3) gives the sunspot number.
     Sunspot numbers may be obtained from Solar-Geophysical
Data published by NOAA.  Daily sunspot numbers are available
and can vary considerably; actual daily sunspot numbers are
preferable to smoothed, averaged or predicted values.  The
sunspot number for the day approximately 3 days before the
observation is the appropriate value to use.  Moderately
accurate predicted monthly smoothed values are available a
year in advance.
     For those who are in a hurry or don't care, the following
table gives observed monthly averaged values until May 1989
followed by the predicted, smoothed values until 1990.  The
estimated uncertainty (90 percent) in the smoothed values is given in
parentheses under the predicted value.

   International Relative Monthly Sunspot Numbers

Year  Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

1980  164 163 161 159 156 155 153 150 150 150 148 143
1981  140 142 143 143 143 142 140 141 143 142 139 138
1982  137 133 129 124 120 117 115 109 101  96  95  95
1983   93  90  86  82  77  70  66  66  68  68  67  64
1984   60  56  53  50  48  46  44  40  34  29  25  22
1985   20  20  19  18  18  18  17  17  17  17  17  15
1986   14  13  13  14  14  14  14  13  12  13  15  16
1987   18  20  22  24  26  28  31  35  39  44  47  51
1988   58  65  71  78  84  94 104 114 121 125 130 138
1989  142 145 150 153 157 163 166 169 176 181 183 185
                         ( 5)(11)(16)(19)(21)(23)(24)
1990  186 187 185 180 174 170 168 166 159 151 144 139
1991  138 134 130 129 130 128 124 119 114 113 115 115

     This option will correct phases for an incorrect antenna
and source position; delays and rates are also corrected.
The corrections to be added to the old values for the x,y,
and z components are given in meters as CLCORPRM(1),
CLCORPRM(2) and CLCORPRM(3). If the coordinates are in a right
handed system then CLCORPRM(4) should be 1.0 or larger.
The corrections to be added to the source position at the picture
plane are given in sec of arc as CLCORPRM(5) for RA direction and
as CLCORPRM(6) for declination.
    The position of antennas are determined in different coordinate
systems for VLA and VLBI.  The X-axis is located in local meridian for
VLA and in Greenwich meridian for VLBI and EVLA.  So CLCORPRM(7) has
to be >0 for VLA and =0 for VLBI/EVLA.
    Note: only one FQ ID is processed per run; if there are
several FQ ID then DFCOR must be run several times.
   A correction for antenna position errors should be made before
further calibration is done.  First,  run DFCOR with OPCODE='ANTP'
using GAINVER=1; GAINUSE=2 to copy CL table 1 to version 2 and then
correcting for the antenna position error(s).  Then run CALIB applying
CL table 2 (DOCAL=1; GAINUSE=2).  Use SNPLT to examine the results to
be sure that the correction was done properly.  When using CLCAL the
input CL table should be version 2 (GAINVER=2).  If there are adequate
observations of calibrators then LOCIT can be used to determine
antenna position errors.

     This option allows entering complex gain corrections
directly into the CL table.  This operation is mostly of use in
the settiong of MkIII VLBI manual phase cals so only the phase
can be specified.  If the amplitudes also should be changed then
TABED can be used to multiply the real and imaginary parts of
the complex gains by the appropriate value.
     Note: the phases in the CL table are corrections to be
added to the data and thus have the opposite sign from the
Haystack convention.  Up to 20 IFs can be entered with
CLCORPRM(1) corresponding to IF BIF, CLCORPRM(2) to BIF+1 etc.
Phases are given in degrees.
     Note: for some reason phase cals read by AIPS are 144
degrees more positive that those decoded by the Haystack
software.  To obtain the sedired results add 144 degrees to any
manual phase cals used in the Haystack system.

     This option is similar to 'PCAL' except that any unblanked
phases are left unchanged.  Any blanked phases are replaced by
the value expected based on any unblanked phases and the
relationship between the IF given in CLCORPRM.  In the case that
all phases are blanked then this option is the same as 'PCAL'.
     This option is intended for use when some phase cals are
present for a given antenna but are missing for some IFs.  This
option allows using the good values and estimating the missing

     This option allows adding values to the IF residual delays.
This correction will not effect the current values of the total
model delay and is intended primarily for correcting MkIII data
for the antenna based difference between the multi-band and
single-band delays.  Individual IF values can be entered but it
is usually assumed in the MkIII system that this is a constant
value for all IF.  In this case fill CLCORPRM with the desired
correction.  Values are given in nanoseconds and will be added
to the current correction, i.e. subtracted from the data when
this table is applied.  The values in CLCORPRM correspond to IFs
BIF, BIF+1, ... EIF.
Having applied this correction the new CL table application
will change the slope of phase frequency dependence inside
the each IF. The change of the slope at each IF is determined
by the value of corresponded parameter CLCORPRM(I). This option
does not change the phase difference between different IF's.

     This option changes the multiple band delay by introducing
the corresponded slope at phase vs frequency dependence. The same
phase is added for all channels of the given IF. Values of
CLCORPRM are given at nanoseconds. The added phase is determined
by the next formula  FI[I]=TWOPI*CLCORPRM[I]*DF[I], where DF[I]
is a difference between the frequency of the given IF and
residual one. The values of multiple band delays CLCORPRM[I] can
be different for different IF, although it is constant typically.
The values CLCORPRM[I] for all IF have to be installed even if
they are the same for the all IF.
The delay corresponded to the first IF - CLCORPRM[1] is substituted
at the modified CL table at MBDELAY1(2) collumn.

     The VLA has four separate 'IFs'.  In normal observing,
the frequencies of these are locked together into pairs.  Each
pair forms an AIPS IF.  In normal observing, the phase
calculation, or finge stopping, is done correctly.
     However, for some spectral line observing, it is desirable
to have the separate VLA IFs of a pair at the same center
frequency, but with different bandwidths.  In this case, the
Signed Sum of the LOs is different and the two frequencies can
not be locked together.  The VLA has only sufficient hardware to
control one IF of each pair, so the fringes for the other cannot
be stopped correctly.  In general, this leads to decorrelation.
However, if the frequency difference is sufficiently small, it
is merely results in a residual phase error, which changes
slowly with time.
     This option is to allow a post facto correction to be made
to the phase only.  Note that the delay is calculated correctly.
The VLA IFs that are affected are 'B' and 'C'.  By convention,
'A' and 'D' are always fringe-stopped correctly.
     Since the error depends upon the antenna location, the
possibility that the antenna coordinates are defined in a left-
handed system is allowed for, even though the VLA uses a right-
handed system.

The correction for SSLO is calculated at each CL table entry
time as follows:

     If A is the antenna position vector and S is the unit
source position vector, then the calculated phase correction
(dph) is

     dph = 2 * pi * [ integer part of ( A . S * dfq / c)]

where dfq is the frequency correction in Hz calculated from

     The new value of the complex gain in the CL table (gnew) is
calculated from the old value (gold) as:

     gnew = gold * exp (i * dph)

or, in cartesian coordinates:

     xnew = xold * cos(dph) - yold * sin(dph)
     ynew = xold * sin(dph) + yold * cos(dph)

where g = x + i * y

     This option changes the delay, rate and phase in accordance
with an antenna axis offset. CLCORPRM(I, I=1, NANTSL) is the
axis offset of antenna I in meters. The AN table is modified
also. Two type of antenna mounts (altazimuth and equatorial)
are supported.