The GBT Gain Curve at High Frequency

Recent measurements at Q-band (43 GHz) have verified the improved performance of the GBT provided by the updated gravity model that was deployed in the fall of 2014. The measured gain curve is indistinguishable from 1.0 over an elevation range from 15 degrees to 80 degrees. This represents a significant improvement on the previous gain curve from 2009 that showed decreasing efficiency below 40 degrees and above 65 degrees elevation. The current estimated surface errors, under good conditions, is 230 microns for the GBT.