[evlatests] EVLA Antenna Feed Moisture Condensation Conflaguration

[Charles Kutz]

During the last two maintenance days, the Front End group dried out the 
following antenna feeds: K-Bands in antennas 1,5,11and 25     C-Bands in 
antennas 17, 19,24 and 26    X-band in antenna 25 which also had a small 
flake of aluminum that had fallen out of the feed and was laying on the 
receiver window.

FE also replaced the destroyed center section "o" ring in the K-Band 
feed of antenna 25, this did not result in a leak in this instance.

In all instances, there were drops of water on the receiver window and 
moisture in the very bottom of the feeds. No moisture was observed at or 
near the top of the feeds, which rules out feed leaks as the culprit. 
The problem is due to condensation.

The cryo shop inspected the desiccants on each of the aforementioned 
feeds and replaced them as necessary.

The discrepant antennas, appear to be providing nominal RF performance 
parametrics at this time.




So until the next soggy humid weather scenario occurs,

Cheers