  We report on laboratory test results of the Compact Water Vapor Radiometer
(CWVR) prototype for the NSF's Karl G. Jansky Very Large Array (VLA), a
five-channel design centered around the 22 GHz water vapor line. Fluctuations
in precipitable water vapor cause fluctuations in atmospheric brightness
emission, which are assumed to be proportional to phase fluctuations of the
astronomical signal seen by an antenna. Water vapor radiometry consists of
using a radiometer to measure variations in the atmospheric brightness emission
to correct for the phase fluctuations. The CWVR channel isolation requirement
of < -20 dB is met, indicating < 1% power leakage between any two channels.
Gain stability tests indicate that Channel 1 needs repair, and that the
fluctuations in output counts for Channel 2 to 5 are negatively correlated to
the CWVR enclosure ambient temperature, with a change of ~ 405 counts per 1
degree C change in temperature. With temperature correction, the single channel
and channel difference gain stability is < 2 x 10^-4, and the observable gain
stability is < 2.5 x 10^-4 over t = 2.5 - 10^3 sec, all of which meet the
requirements. Overall, the test results indicate that the CWVR meets
specifications for dynamic range, channel isolation, and gain stability to be
tested on an antenna. Future work consists of building more CWVRs and testing
the phase correlations on the VLA antennas to evaluate the use of WVR for not
only the VLA, but also the Next Generation Very Large Array (ngVLA).
