K and Q band receiver status

K-band sensitivity/system temperatures:

• As of May 2003, 26 VLA antennas are equipped with new K-band receivers.
• AN 14 is the only antenna having an old K-band receiver.
• AN 13 is currently being upgraded to an EVLA antenna, and will thus soon have a receiver with larger tuning range.

Typical system temperatures are 40-80 K, depending on the weather conditions (100-150 K for the old receiver in AN 14). With 26 new and 1 old receivers in the array, the expected rms noise in an image should be estimated by using K=17 in the VLA Observational Status Summary sensitivity equation.

Below is a plot of the system temperature (solid red line) versus observing frequency. The data was taken during night time in May 2003, under very good weather conditions. This plot shows that the system temperature is stable across the band.

The new K-band receivers have for some time suffered from water contamination during wet weather, when the system temperatures increased up to 50-200 K. Successful leakage repairs have been made of those receivers during the spring and summer 2002.

K-band tuning range:

The nominal receiver range is 20.6 - 25.2 GHz, with the default K-band continuum frequencies near 22 GHz. The band edges are limited by the LO tuning capabilities. This constraint will not be lifted until the EVLA is complete. The plot below shows, at the time of the test, how many antennas which successfully locked at the given frequency (blue dots).

Q-band sensitivity/system temperatures:

As of May 2003, 28 Q-band receivers are now available.

The typical system temperature at zenith is 80 K. The expected rms noise in an image should be estimated by using K=35 in the VLA Observational Status Summary sensitivity equation. Below is a plot showing the system temperature as a function of observing frequency. As is the case for the K-band receivers, the band edges are determined by the LO tuning capabilities.

Q-band tuning range:

The nominal receiver range is 40-50 GHz, with the default Q-band continuum frequencies near 43 GHz. The plot shows (with blue dots) how many antennas which locked at each observing frequency.

Aperture efficiency:

In parallel with the Q-band outfitting, the antenna panels have been readjusted using 43 GHz holography to improve aperture efficiency (see VLA test memo 234). These panel adjustments lead to forward gains for the VLA antennas between 30% and 40% at 43 GHz.