[evlatests] How Fast Can We Step?

[Rick Perley]

     With the current system, phase/delay stepping is limited to about 
0.7 Hz (a step every 1.5 seconds).  This is much to slow for sky surveys 
done at high frequencies, where the primary beam crossing time can be 
less than 2 seconds.

     The dominant limitation is in the station board.  Bruce made a 
change to permit faster stepping.

     I ran a short test this morning, using 3C48, and an antenna motion 
of 1 arcminute/second (4 X 'sidereal').  Dump time was 0.1 second.  The 
phase/delay center was moved at four different rates: 1.5 seconds, 1.0 
seconds, 0.75 seconds, 0.5 seconds.  The scans were in RA, and utilized 
the 'back-and-forth' method (for future analysis), going from first null 
to first null.

     Results:

     1) The three slowest rates are all good.  The system easily keeps up.
     2) The fastest rate (2 Hz) gave a mixed result:
            a)  For the W to E motion, the system could not quite keep 
up -- many of the initial delay/phase models were incorrect.
            b)  For the E to W motion, all was fine.  No incorrect 
calculations.

     Bruce says he can speed it up a little more.  Shall we try?

     Rick