Current Events: Difference between revisions

Revision as of 15:36, 2 January 2008

Current Events

Dec 20, 2007 Antenna Installation Part 1: The pedestal has been put up on the new foundation. The sidearm-counterweight modifications are complete and the antenna has been installed on the pedestal.

Aug 16, 2007 Pedestal Work

The installation of the new dual-offset antenna was delayed several months to allow for some necessary pedestal refurbishment.

Aug 3, 2007 RF Instrument Lab: A new dedicated RF instrument laboratory room was created at the CHILL facility, sporting some of the latest test equipment from Agilent and Tektronix.

July 6, 2007 Pouring a new foundation for the pedestal and radome: The new radome required a larger setback from the site boundaries. Consequently, the site was expanded to the east, and a new foundation was prepared just to the northeast of the previous radar location.

June 1, 2007 Site Preparation: The summer of 2007 is noteworthy for the CSU-CHILL Facility in that we are experiencing the culmination of years of work and planning on the new dual-offset feed antenna. Although this started as a colaboration with Vertex/RSI to develop a new 8.5m Gregorian antenna for the radar, it expanded in scope to build a new foundation and radome to house the system. The site wiring will also be extensively updated and upgraded to a more permanent installation.

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 ;[[Dec 20, 2007 Antenna Installation Part 1]]
-:At last the site preparations are nearly complete and the pedestal was also ready to be fitted with the new antenna.  Kyle Hollwarth, the mechanical designer of the antenna, and a two-man crew came to conduct the preparatory steps prior  to antenna installation.  The original sidearm/counterweight assemblies were modified to accept the additional counterweight required for the heavier antenna. In addition a cross-member I-beam was fitted across the top of the two sidearms.  This resists the possiblity of differential torque between the sidearms stressing the antenna structure.  It also limits the upward elevation movement to 96 degrees or less.  This is required due to the fact that the center of the dish is now offset some 5 or 6 feet above the elevation axis.
+:The pedestal has been put up on the new foundation.  The sidearm-counterweight modifications are complete and the antenna has been installed on the pedestal.
-: In spite of a cold spell at the Greeley site, and several snowfalls, these steps were completed.  The pedestal was rebuilt on the new pad, the antenna was put together on the ground, and finally hoisted into position on the new sidearms.  All that remains at this point is to mount the sub reflector and feedhorn, and finally to check the surface accuracy and antenna geometry by using photogrammetry.  These steps are expected to commence on January 7th, 2008.
 ;[[Aug 16, 2007 Pedestal Work]]
-:Operations were suspended at the end of June to allow for replacement of the main azimuth bearing.  The pedestal is a big heavy item (24,000 lbs) which requires a certain amount of heavy lifting to replace the azimuth bearing.  Fortunately, we were able to use NCAR's Marshall lab high bay garage so much of the work could be conducted inside.  The CHILL pedestal uses a king-post design with a cross-roller main bearing at the top of the king-post, and a radial roller bearing about two feet below to resist the overturning moment.  When the main bearing was removed it was found to have indeed failed and was shedding hardened metal flakes. Since the recirculating oil lubrication in use at CHILL would likely take these metal flakes through the lower bearing also, the entire rotating part of the pedestal was lifted off to expose the lower  bearing.  The lower bearing did show the imprint of the metal flakes on the bearing surface, so a replacement was sought.  This two piece bearing proved impossible to find in stock, but Jack Fox and Karl Schwenz of NCAR's Design and Fabrication Service were able to adapt a standard ball bearing to the kingpost.  This one-peice ball bearing proved more difficult to install than the original, but it is now in place and appears to be working well.
+The installation of the new dual-offset antenna was delayed several months to allow for some necessary pedestal refurbishment.
-:The sliprings have to be removed to replace either of the azimuth bearings.  Upon inspection, it was found that the lower slipring bearing had completely failed and taken out several of the lower brushes as well. Since these sliprings had been in service for 35+ years, they were sent back to the original manufacturer (Fabricast) for refurbishing. The bearings were replaced, the rings were polished, and the brushes were replaced restoring the unit to like-new condition.  The only downside of the refurbishment is that it took about 8 weeks to complete.
 ;[[Aug 3, 2007 RF Instrument Lab]]

Current Events: Difference between revisions

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