[evlatests] EVLA2 and EVLA3 C-band Performance

[Emmanuel Momjian]

Test observations at C-band have been carried out yesterday to look at 
the performance of EVLA3 and assess the cross polarization on the 
EVLA2-EVLA3 baseline (i.e. using the two antennas that have the new 
wide-band C-band OMTs).

The observations covered the frequency range 3835-8235 MHz, tuning at 
every 100 MHz and using 50 MHz bandwidth per frequency setting. The 
observed source was 3C147.

Results:

1) Effective System Temperature: Both EVLA2 and EVLA3 have comparable 
values in Tsys/efficiency which are around 70 to 80K (depending on the 
frequency). In the VLA frequency range (i.e ~4.5-5.1 GHz), these two 
antennas are worse by about 10K compared to other EVLA antennas. EVLA3's 
IF D seems to have a problem of its own, as its effective Tsys is worse 
by a factor of 2 compared to the same IF of EVLA2 or compared to the 
other IFs of EVLA3.

2) Cross Polarization: Both RL and LR (normalized with respect to 
parallel-hand polarization) for the baseline EVLA2-EVLA3 have been 
measured between 3.8 and 8.2 GHz. Excluding the edges of the band, the 
measured values are very low, and typically between 3% to 4% (+/- 1%). 
The cross polarization performance seems to meet, and even exceed, the 
project requirements.

Emmanuel