[evlatests] Polarization Results

[Rick Perley]

    Some very interesting polarization results to report from the 3C147 
observation.

    This is a completely unpolarized source, so the polarization 
characteristics reported below are due to the antennas alone. 

    1) Bandpass.  A BPASS was done, and showed the usual sinusoidal 
wobbles, of typically 15 MHz period, and about 5% amplitude.  One 
antenna stands out -- antenna 25, in RCP has a *much* larger 
oscillation, of period 20 MHz, and whopping 12% amplitude.  This 
corresponds to a free-space distance of 7.5 meters -- there is a serious 
mismatch somewhere in the signal path for that IF on that antenna. 

    2) Bandpass Stability.  Plots of the calibrated bandpasses, made 90 
minutes apart, show the bandpass stability to be quite good.  But not 
perfect.  There is on *all* antennas a slowly varying component, of 
about 0.5% amplitude, and 30 MHz period (corresponding to 5 meters 
distance). 

    3) Polarization amplitude.  All baselines showed from 0.4 to 0.8 Jy 
in polarized signal.  The source has 18 Jy of unpolarized intensity, so 
the polarized response is typically 5% of the total -- agreeing with 
what we expect from the antennas alone. 

    4) Polarization frequency structure.  There is a remarkable 
frequency pattern, showing sinusoidal oscillations of remarkable 
modulation -- up to 50% for some baselines.  The period is quite short 
-- about 12.5 MHz, and is the same for all baselines.

    5) Polarization stability.  Both the amplitude, and the 
characteristics of the frequency structure are very constant.  The 
spectral plots of the cross-polarization show no variation in amplitude 
or phase over the 90 minute duration of the observation.