[evlatests] Phase Jumps and the Flukes

[Rick Perley]

    A test was run today to test Barry's hypothesis that changing 
frequencies by a value selected so that the Fluke synthesizes are 
incremented by a multiple of 10 MHz will result in no phase jumps.

    Barry is correct. 

    Here are the details.

    The first 30 minutes of the 60 minute test alternated between two 
frqeuencies, 1465 and 1445 MHz for IF #1, and 1385 and 1405 MHz, for IF 
#2.  These values were selected so that the frequency change could be 
set by the Flukes alone (i.e., the L6 settings were made identical).  
Specifically:
   
       1465/1385:      L6:  3640 and 3560,    Flukes:   121.975 and 221.775
       1445/1405:      L6:  3640 and 3560,    Flukes:   101.975 and 241.775.

    (Ken reminded me that it is insufficient to change the frequency by 
10 MHz, as the Flukes running the B and C IFs increment by half that set 
for A and D). 

    During this first 30 minutes, I alternated back and forth, with a 
one minute integration. 

    The second 30 minutes were spent in the same way, but with a pair of 
frequencies that were NOT different in frequency by a multiple of 20 
MHz, but which also used the same L6 setting.  Specifically

       1465/1385      L6:  3650 and 3560      Flukes:  121.975 and 221.775
       1450/1390      L6:  3650 and 3540      Flukes:  106.975 and 226.775

    For all observations, the BW was 6.25 MHz. 

    Results:

    For the first pair of frequencies (which differed by 20 MHz), all 
phases are rock steady.  There are no jumps. 

    For the second pair of frequencies, there are many 'global' phase 
jumps -- all of them of the exactly 180 degree variety.  The 
characteristics of these 180-degree jumps are identical to those 
reported earlier (in the five or seven L-band frequency tests:)
       All VLA antennas jump identically. 
       The RCP and LCP sides, for a given IF, jump identically.
       The two IFs do not jump in synchronism.  For example, for IF1 at 
1465 MHz, the VLA was in the 'up' phase statesfor eight of the 13 
observations, and in the down (by 180 degrees) state for five.  But IF 
#2, at 1385 MHz, the 'up' state was seen in four scans, the 'down' in 
nine.  Meanwhile at the other frequency pair (1385 and 1390 MHz for IF 1 
and 2, respectively), the patterns were quite different:  IF1:  7 ups 
and 6 downs;  IF2:  5 ups and 8 downs.  There seems to be no correlation 
between changes between up and down between IF pairs or frequencies. 

      It is interesting to note that the 72-degree regular phase 
advancement (or retardation) noted in my multiple, cyclic frequency 
tests two weeks ago, is entirely absent.  The only jumps in this 
database are by 180 degrees.  Given the manner in which the Flukes were 
commanded, it seems pretty clear that the 180 degree family of phase 
phenomena originate with the Fluke synthesizers.