[evlatests] High frequency sensitivity/tuning

[Rick Perley]

    As part of preparing for a 24-frequency polarization experiment (8 
frequencies in each of K, Ka, and Q bands), I tested system capabilities 
for a short while yesterday afternoon.  Weather was quite poor for high 
frequency operation (thunderstorms, wind, etc.) -- it's remarkable 
things worked as well as they did. 

    Some interesting problems were found:

    a)  K-band. 

    Antennas 15 and 23 did not tune to 20.515 MHz in IFs A and C.  The 
failure occurred both times in two different observations. 
    Antenna 13 has noticeably poorer sensitivity than the others at all 
frequencies -- a factor of at least two worse. 
    Antenna 24 in IF 'B' only has poor sensitivity at the two highest 
frequencies attempted (23.7 and 26.0 GHz).

    b) Ka-band.

    Antennas 9 and 24 have poor sensitivity -- a factor of two or more 
worse than the others -- at all frequencies. 
    Antenna 1, IF 'B' did not tune at all for three of the four 
frequencies it was commanded to:  32.375, 30.575, and 28.775 GHz.  It 
did tune to 26.975 GHz. Curiously (and uniquely!), IF 'A' tuned 
correctly for all four.  (All other apparent failures to tune involve 
both polarizations of a given IF). 
    Antenna 28 gave no fringes at all -- I believe this is a known 
problem. 

    c) Q-Band. 

    It's difficult to make  global assessments, due to weather.  It 
seems clear that antenna 24 is notably less sensitive than others.  This 
is significant since before its recent move, it was the best, or nearly 
the best, Q-band antenna. 

    Much more information will be available after our long polarization 
run, Friday evening.