[evlatests] set-and-remember test results

[Rick Perley]

    Tests of the 'set-and-remember' observing mode were done Friday 
afternoon.  The test was to observe 3C84 for one hour, switching between 
C and X bands every 30 seconds.  A pretty stern test.  Ideally, there 
will be no amplitude changes (that cannot reasonably be accounted for by 
atmospheric or pointing effects) throughout each band's observations. 

    Results:

    A) At C-band, the gain stability looks quite good, with one notable 
exception:  Antenna 26 has two different amplitude states in RCP, and at 
least 3 in LCP (plus some other bizarre phenomena).  In RCP, the two 
states are separated by 1 dB in power. 
    The weather must have been rather poor -- there are small (< 1%) 
changes in cross power on most antennas, acting on plausibly atmospheric 
timescale, well correlated between the two polarizations. 

    B) At X-band, the situation is much more confused.  Most antennas 
behave as at C-band, with somewhat larger (but still small) amplitude 
changes well correlated between polarizations.  I would again interpret 
these as the effects of a bad weather day.  But there are some 
spectacular exceptions:
    Antenna 15 has two amplitude states, in both polarizations.  But the 
step in amplitude is 15%, corresponding to 1.2 dB -- rather farther from 
1 dB than I had expected.  Is this reasonable? 
    Antenna 26 is quite bizarre, with four different amplitude states, 
again separated by rather more than 1 dB. 
    Antennas 14, 16, 18, 23 and 24 are showing apparent gain stability 
variations which are not plausibly atmospheric (they change in 
synchronism with the switching), and are different between the two 
polarizations. 

    The ordering of the IFs at X-band is still reversed, as noted earlier.