VLA Test/Observation Coordination Meeting B.G. Clark August 18, 2005 1. EVLA Antenna 16 has had four working IFs. The hardware situation remains somewhat unstable, so that the first thing to do for any test time is to find out what is working. A four IF system is being installed in antenna 14. There is some possibility it may work today. R. Perley reports on K band tipping curves obtained in late June. At frequencies of 18.4, 23.5, 26.1 GHz, the system temperature, extrapolated to zero atmosphere, was 35, 30, 33 K, and zenith opacities were 0.02, 0.05 and 0.03 respectively. The higher opacity at 23.5 GHz reflects water vapor absorption. Actual antenna efficiencies depend on observations of planets, which have not yet been made. At Q band frequencies of 40.5, 43.4, and 48 GHz, the corresponding system temperatures were 39, 50, and 61 K, and zenith opacities of 0.055, 0.07, 0.11. The higher opacity at 48 GHz reflects the oxygen absorption band. A rather inadequate observation of Jupiter yields an efficiency of about 30%. P. Napier reports that the round-trip phase meters have been installed on antenna 16. The comparison of the two meters, with the same inputs, indicates that they agree to about 0.4 ps (7d at 50 GHz) over 30m. There are, of course, large diurnal (presumably thermal) effects noted, and a single episode of antenna movement resulted in a change of about 7 ps (120d at 50 GHz). More measurements and tests to come. 2. 200 MHz system R. Perley reports on current status. On only one antenna has a careful measurement been made of the effect of the system on the 327 MHz system. On this antenna, the presence of the 200 MHz feed (with its leads shorted), actually seems to improve the 327 MHz performance, increasing the efficiency and making the beam rounder. The beam of the 200 MHz feed is much as one would expect from an out-of-focus feed. It is much better looking than the 327 MHz beam (because it is out-of-focus by a smaller fraction of a wavelength) or the 75 MHz beam (which has too few wavelengths across the dish). The digital TV stations on channels 9 and 10 make things very difficult at the high end of the band. At the bottom end of the band, there might be a reasonably clear band of up to two MHz between the audio and visual carriers of channel 8, which might be available for non-spectroscopic observers. This channel apparently is not occupied by a DTV station in New Mexico at the moment.