[evlatests] ea09 LCP weird birdie

[Rick Perley]

    And another very strange birdie has been found:  -- only on 
baselines to ea09, and only in LCP.  The frequency is very unusual -- 
1813 MHz.  This birdie is of finite width -- wider than the spectral 
resolution (1 MHz).  It is seen on many, but not all, baselines to ea09, 
and on no others. 

    Even more peculiar, and probably related, is a rhymic (sinusoidal) 
variation in amplitude and phase, of magnitude a few percent, seen on 
*all* the baselines to ea09 in LCP, in the uppermost channels of subband 
13 and the lowest channels of subband 14.  (That is, within about 4 MHz 
of 1841 MHz).  Unlike all other 'birdies', this feature appears to have 
the same temporal frequency (in both amplitude and phase) for all 
baselines at one time.  (I'm checking the time variability next).   I 
bet this is not an external birdie at all -- it should have highly 
suppressed by the subband 'notch' if it were -- and is something 
internal which has been amplified to prominence by the bandpass 
correction function. 

    There is a striking similarity of this to the effect I found early 
this year at Ku and K bands, while in A configuration, on some baselines 
and in some subbands -- which has never been fully explained.