To add 2.4 and 33 GHz observing bands at the Cassegrain focus we must rearrange the feeds on the VLA feed ring and install a new feed enclosure. A structure more like the VLBA feed cone will likely be used. Support of multi-band performance (§1.2.6) would entail additional modifications.
Modifications to the antenna quadrupod and FRM are needed to support the proposed higher-efficiency prime focus systems: the 600 MHz system, a broadband UHF system, or a cooled 800-1200 MHz receiver. For the first two options, the quadrupod must be lengthened to allow siting these systems at the prime focus (at present, the 330 MHz feed is out of focus). For the 800-1200 MHz system, we need to study how to optimize the desire for sensitivity (e.g., to search for redshifted HI in emission or absorption) versus the added weight of a refrigerator. Lightweight (Sterling) refrigerators will alleviate the problems. The effect of modifications to the quadrupod structure and the FRM, together with the weight of a feed and cooled receiver, could conceivably cause excessive gravitational deformation of the primary reflector. This must be checked by structural analysis.
Performance in the 40-50 GHz band requires some effort to improve the surface quality, pointing accuracy, and tracking accuracy of the antennas that are not now outfitted for this band. The methodology for measuring and adjusting the primary reflectors is now well understood.