[evlatests] 4band, interference and ea14

[Rick Perley]

In the (distant) past, a similar effect was commonly noted at 4-band.  
The accepted explanation was either that:

     1) An exceptionally bad antenna is radiating to the others. This 
would be most prominent in D configuration.
     or
     2) The supposedly incoherent LOs are sufficiently close in 
frequency that, for periods of seconds to tens of seconds, there is 
insufficient phase slip between them to destroy the cross-correlation.

     I recall that #2 was in fact the theory I came to embrace, as it 
was usually noted that the baselines with strong combs were independent 
of antenna location.

     You could test this by looking at the phase of the line 
cross-correlation.  If from a single source (i.e., theory #1), the phase 
should slip with the fringe rate.  But if from different LOs with 
slightly variable phases, the phase relation will be 'different'.  (I'm 
not prepared to define 'different', other than it won't be strictly the 
same as the fringe phase).

     Rick


Interestingly the 5MHz comb frequencies correlate on baselines to 14 (as 
they do on 12-19). Since the 5MHz clock is supposed to be incoherent 
from antenna to antenna, there must be a general source of the comb 
frequencies, especially 60MHz, which is being broadcast around the site. 
Could this be one very bad antenna ? ---Frazer 
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