[evlatests] PDif compression tests, continued

[Rick Perley]

    Keith and Brent put attenuators in at the L-band receiver ouputs in 
antennas 5, 6, and 15 to place the power levels at the input to the T304 
to within the nominal range.  We then ran last night the L-band 'Cygnus 
A' test to test whether the PDif compression on these antennas was 
repaired.  These values were taken with the T304's attenuators set to 
the standard levels. 

    Answer:  PDifs are much better now, but still not at the correct 
values -- small compression remains. 

    We have comparable data for ea05 and ea06.  Below is the 'before and 
after':

    BEFORE:
   Antenna          A           B            C           D
------------------------------------------------------------
    ea05             .75           .76         .59         .72
    ea06             .92           .70         .86         .85

    AFTER:
    ea05             .96           .95         .80         .88
    ea06             .96           .93         .90         .96
------------------------------------------------------------

    So, there is a marked improvement for both, but a significant 
compression still occurs (particularly for ea05 in LCP). 

    For the record, I give below the PDif compression values, on Cygnus 
A, for all antennas. 

    Antenna         A             B           C            D
---------------------------------------------------------------------------
    ea01             .82           .84         .86          .87
    ea02             .88           .87         .77          .81
    ea03             .91           .95         .71          .87
    ea04             .81           .87         .80          .84
    ea05             .96           .95         .80          .88
    ea06             .96           .93         .90          .96
    ea07             .96           .95         .96          .93
    ea08             .90          1.00        .94        .92
    ea09             .95           .91          .98        1.00
    ea11            1.00           .98        1.00       1.00
    ea12              .91           .89         .93          .93
    ea13             1.00         1.00        .75          .78
    ea14              .99           .93         .94         .95
    ea15              .99           .96         .97       1.00
    ea16              .93           .88         .90          .91
    ea17             1.00         1.00        .97       1.00
    ea18               .85           .77        .55         .67
    ea19             PDif on Cyg A too noisy!
    ea20              .88           .85         .85         .88
    ea21              .77           .78         .88         .75   
    ea22              .88           .86         .73         .80
    ea23            ???            .91         .77          .85
    ea24              .81          .76         1.00       1.00
    ea25              .51          .55          .75          .67
    ea26              .86          .91          .91          .88
    ea27             1.00        1.00        1.00        1.00
    ea28               .97        1.00          xxx       xxx
---------------------------------------------------------------------

    Notes:   ea19's compression is very small, but is hard to determine 
accurately, since the noise in PDif is extremely high -- especially on 
the observations of Cyg A.  The fluctuations, while on Cyg A, exceed a 
factor of four -- many times higher than for other antennas.  But, while 
on cold sky, the PDif fluctuations are about 25% -- higher than normal.  
Something is rather odd with this antenna. 
     ea23A's switched power does not seem to be working at all.
    ea28C and D (LCP) switched power not functioning correctly.