Q Band receivers are installed on only 10 VLA antennas, whose aperture efficiencies are about 20% and are still being improved by holography and focus adjustments. The optimal layouts for these antennas during each VLA configuration are still being explored. The nominal tuning range for the receivers is 40-50 GHz, but the aperture efficiency falls by about a factor of two between 43 and 49 GHz while the system temperature increases by about a factor of two. The details of the performance across the whole band are still being investigated.
The sky opacity at Q Band is dominated by an atmospheric 
line at 60 GHz so it varies little with the
weather; typical zenith opacities are 0.06 at 43 GHz
and 0.15 at 49 GHz. Plan about 10 minutes to determine the zenith sky
opacity from a total power tipping scan during your observations.
Phase coherence varies greatly from day to night. Under poor day-time conditions, phase referencing on SiO maser sources or self-calibration are essential. Under dry night-time conditions, external calibrations on time scales of 10-20 minutes are also likely to succeed.
Because of the small (1') primary beam size at Q Band,
accurate pointing is critical to Q Band observing and
you should plan to make reference pointing observations at X Band
about once an hour throughout Q Band observing. Reference pointing
scans should take about 4 min. It is important to select
reference pointing calibrators as close as possible to, and definitely
within 
in azimuth and elevation of, your target sources.
The phase calibrator is often a good choice for the reference pointing
calibrator. If possible, choose a pointing calibrator with a smaller
right ascension than your target, so the target drifts through the
reference pointing position during the observation. Avoid observing
sources within 
of the zenith.
As the Q Band system on the VLA is relatively new and the NRAO staff and users are still gaining experience with it, information about Q Band performance and optimal observing strategies is changing rapidly. It is therefore a good idea to consult the Q Band page on the World-Wide-Web (http://www.nrao.edu/doc/vla/html/Qband/qband.shtml) for updated information before finalizing Q Band observing plans.