[daip] Wrong (u,v) coordinates?

[Arnaud Collioud]

Dear Eric,

After the BLAPP problem, I am encountering a new un-expected problem.
I successfully processed my multi-source S-band VLBI experiment (ending with SPLIT, then FITTP). But when loading the individual data in Difmap (or just looking at it in AIPS by UVPLT), the uv radius values are very low compared to the expected ones.

For example, on a given baseline at a given time, I have these (u,v)-coordinates and uv radius:
At X-band (8.646 GHz)
	u = -20.886 MLambda
	v = -342.66 MLambda
	uvrad = 343.29 MLambda

At S-band (2.309 GHz)
	u = -1.482 MLambda
	v = -24.309 MLambda
	uvrad = 24.3547 MLambda

The X-band values are typical for this kind of session (VLBI). But, the expected S-band values in this case are the X values divided by the frequency ratio (X/S = 8.646/2.309 ~ 3.744).
The real ratio here is around 14.1 (which is almost (X/S)^2 ???).

I suspect a frequency issue.
But where should I look first to control my processing? Did someone already report such a problem?

I put the results of IMHEADER and PRTAB of the FQ table below. I did not notice anything wrong in these...

Thank you very much!
Cheers,
Arnaud

*******************


>imh
AIPS 1: Image=MULTI     (UV)         Filename=IYA09_S.CLN .UV    .   1
AIPS 1: Telescope=VLBI               Receiver=MKIV
AIPS 1: Observer=Bonn Cor            User #=    4
AIPS 1: Observ. date=18-NOV-2009     Map date=03-JUL-2014
AIPS 1: # visibilities   4848889     Sort order  TB
AIPS 1: Rand axes: UU-L-SIN  VV-L-SIN  WW-L-SIN  TIME1  BASELINE
AIPS 1:            SOURCE  FREQSEL  INTTIM  WEIGHT  SCALE
AIPS 1: ----------------------------------------------------------------
LOGFILE FOR USER    4 GETTING LARGE: USE PRTMSG AND CLRMSG NOW!
AIPS 1: Type    Pixels   Coord value     at Pixel     Coord incr   Rotat
AIPS 1: COMPLEX      1   1.0000000E+00       1.00  1.0000000E+00    0.00
AIPS 1: FREQ        32   2.2329900E+09       1.00  2.5000000E+05    0.00
AIPS 1: STOKES       1  -1.0000000E+00       1.00 -1.0000000E+00    0.00
AIPS 1: IF           4   1.0000000E+00       1.00  1.0000000E+00    0.00
AIPS 1: RA           1    00 00 00.000       1.00       3600.000    0.00
AIPS 1: DEC          1    00 00 00.000       1.00       3600.000    0.00
AIPS 1: ----------------------------------------------------------------
AIPS 1: Coordinate equinox 2000.00
AIPS 1: Maximum version number of extension files of type FQ is   1
AIPS 1: Maximum version number of extension files of type CL is   3
AIPS 1: Maximum version number of extension files of type HI is   1
AIPS 1: Maximum version number of extension files of type BS is   1
AIPS 1: Maximum version number of extension files of type AN is   6
AIPS 1: Maximum version number of extension files of type NX is   1
AIPS 1: Maximum version number of extension files of type SU is   1
AIPS 1: Maximum version number of extension files of type FG is   1
AIPS 1: Maximum version number of extension files of type GC is   6
AIPS 1: Maximum version number of extension files of type TY is   6
AIPS 1: Maximum version number of extension files of type SN is  12


*******************

> prtab
localhos  PRTAB(31DEC14)      4     07-JUL-2014  11:58:49    Page    1
IYA09_S.CLN .UV    .   1  Disk= 1    FQ Table version   1
Title: AIPS UV DATA FILE FREQUENCY TABLE
Created by      UVCOP on 03-JUL-2014 15:32:12
Last written by UVCOP on 03-JUL-2014 15:32:12
Ncol 6  Nrow 1    Sort cols:
    Table has     1 keyword-value pairs:
   NO_IF    =            4
   Table format incompatable with FITS ASCII tables

COL. NO.         1              2                 3               4              5             6
     ROW      FRQSEL      IF FREQ            CH WIDTH        TOTAL BAND      SIDEBAND      BANDCODE
F NUMBER                  HZ                 HZ              HZ
       1         1        0.000000D+00       2.500E+05       8.000E+06           1
       1                  3.000000D+07       2.500E+05       8.000E+06           1
       1                  1.200000D+08       2.500E+05       8.000E+06           1
       1                  1.400000D+08       2.500E+05       8.000E+06           1