[evlatests] Results from 7.5 GHz tests

[Rick Perley]

    Michael and Ken took a hour's data on 0217+738, using four sub-bands 
centered at 7180, 7308, 7436 and 7564 MHz -- at the top end of C-band.  
Only six of the 10 antennas connected to WIDAR have wide-band OMTs.  
These are  2, 3, 9, 18, 24 and 28.  The scans were all one minute long. 

    Removing the four unequipped antennas, and flagging the channels 
corresponding to the big RFI birdie at 7273.5 MHz resulted in superbly 
calibrated data.  There are *NO* 180 deg phase flips, and *NO* 1 dB 
attenuator changes. 

    The bandpasses were solved in the usual way, with one solution for 
each 1-minute scan.  Stability was excellent. 

    A 'pseudo-continuum' database was made by coherently summing over 
950 channels, applying the bandpasses and gains. 

    UVFIX was needed to recover the (u,v,w), which mysteriously were all 
set to zero.  (Michael suspects something to do with the 
autocorrelations being present in this database -- the first time this 
has happened.  The autocorrelation spectra all look quite correct.)

    None of the oscillating amplitudes or phases which have plagued our 
earlier C-band data were seen.  But this should not be too great a 
surprise -- all baselines which have shown this feature in the past are 
formed from the four antennas removed from this database (not equipped 
with wide-band OMTs). 

    An image was made with the six remaining antennas.  The nearby 
'lumpy' structure was noted, as usual.  DR = 18,000. 
   
    BLCAL was run, with significant solutions, typically at the 0.1% 
level. 

    The resulting image (with BLCAL applied) was fabulous -- dynamic 
range of 80,000:1. 

    Thus, I conclude:

    1) The oscillating phase/amplitude problem does not affect the DR. 
    2) The closure offsets seen at 4800 MHz are still with us at 7500 
MHz, using the same receivers.    They do not seem to be present in 
X-band data at 8400 MHz. 
    3) These offsets do not significantly change over a time of one  hour. 

    I'd like to see some L and K band data (taken in good weather for 
the latter), of this source.