Analysing the results

When the observations are completed, EARLY will display the results for each antenna. An example looks like this:

Antenna 1

    0     -0.01    -0.01             -0.01    -0.03
    0      0.00     0.00              0.00     0.00
   45      7.69    -0.06              0.04    -0.03
   45      7.69    -0.07              0.04    -0.03
   90      7.69    -0.05              0.00    -0.07
   90      7.68    -0.04              0.00    -0.07
  135      7.71    -0.06              0.09    -0.04
  135      7.70    -0.07              0.07    -0.06
  180      7.73    -7.85              7.77    -0.06
  180      7.74    -7.84              7.78    -0.06
  225      7.73    -7.80              7.76    -7.73
  225      7.71    -7.82              7.75    -7.77
  270      7.75    -7.84              7.75    -7.80
  270      7.75    -7.84              7.73    -7.83
  315      7.75    -7.85              7.81    -7.80
  315      7.73    -7.84              7.78    -7.80
Sampler phase increments (IFs 1-4):   -157.5   -22.5   -22.5    22.5
Accept, revise or next antenna (A/R/N) [A] :

Following the title is the antenna number, and then columns of data indicating the sampler phase offset (in the first column, in degrees) followed by the adjusted delay values for each intermediate frequency (IF, also referred to as a conversion chain).

The values should be either near-zero or near $\pm7.8125$. If they are not, then they will be printed in reverse video. An example of a failed calibration is shown here (NB: most of these fields would displayed in reverse-video):

Antenna 4

    0     -0.01     0.03             -0.04     0.03
    0      0.00     0.00              0.00     0.00
   45      0.97    -0.96              0.95    -0.94
   45      0.98    -0.96              0.96    -0.96
   90      1.95    -1.96              1.92    -1.96
   90      1.94    -1.95              1.94    -1.94
  135      2.91    -2.92              2.89    -2.90
  135      2.92    -2.93              2.90    -2.89
  180      3.90    -3.89              3.86    -3.90
  180      3.92    -3.89              3.90    -3.90
  225      4.87    -4.86              4.85    -4.86
  225      4.86    -4.87              4.85    -4.85
  270      5.84    -5.86              5.82    -5.86
  270      5.86    -5.84              5.84    -5.85
  315      6.82    -6.81              6.81    -6.81
  315      6.83    -6.82              6.80    -6.81
Sampler phase increments (IFs 1-4):     22.5    22.5    22.5    22.5

What we are doing is slowly offsetting the sampler phase, looking for the point at which the antenna flicks from using the early signal to the normal signal. When we find this point, we set the sampler phase the 180 degrees from this point. This ensures that the clock setting is as far from the edge as possible.

When examining the data, the reverse-video flagging is a good guide to how good the data is, although the discerning observer will look at the data and compare his or her estimate of the appropriate offset with the offset recommended by the EARLY program. This means that if the jump occurs at a phase of 180 degrees, then there should be no adjustment made. If the jump occurs at about 0 degrees, then an offset of 180 should be entered.

Your options at this point are:

Accept, revise or next antenna (A/R/N) [A] :

• Accept (the default) means to accept the values that the program is offering for that antenna.
• reviseis the option you should choose if you think you know better.
• next antenna means to skip this antenna and perform no corrections to it. It might be out of the array for some reason during the calibration, but you have no reason to suspect it to have a bad early/normal calibration.

You have to answer this question, for each antenna.

When the EARLY program has finished you will need to run CACAL.

The data is logged in the file $ATCA_LOG:early.log, just in case.