[evlatests] X-Band Mods on EVLA 14 & 16

[Robert Hayward]

Just a heads up to let you know that we are now using VLA-style X-Band 
receivers on both Antennas 14 & 16. This means that they will have lower 
output level than the modified receivers we have bee using.

Specifically, the cascaded post-amps on the X-Band in Ant 14 have been 
removed. On Ant 16, the receiver was replaced with S/N 41. The original 
unit will be returned to the AOC to have the beefier post-amps removed 
and the original amps swapped back in, where upon it will be installed 
on Ant 18 in a couple of weeks.

As a result, the RF Attenuators on the T304's should be set to 0 dB 
(Barry's setup script already does this) and the Output Attenuator will 
end up being in the 10-15 dB range to produce the canonical -33 dBm 
output level.

Finally, we found some curly bits of metal (and 2 bugs) on the vacuum 
window of the X-Band receiver on Ant 16 before we swapped it out. This 
undoubtedly is the cause of the high cross-polarization that Ken was 
seeing last week.