First Pixel tests with Feed at offset locations

On October 6, 2008 from midnight to 8:00 AM, Steve White, Bob Simon and Glen Langston ran tests of the first pixel of the K band Focal Plane Array. We measured the system performance by peak and focus observations of 3C48 at 19 and 25 GHz with the feed located in the nominal center position and also offset in the cross elevation and elevation positions.

The test report describes the measured intensity as a function of feed offset location.

To summarize the report, we measured the intensity of the reference calibration source, 3C123, as a function of feed position. We made three sets of measurements at two frequencies, 19 and 25 GHz.

The change in gain with feed position was determined by taking the ratio of intensity at the offset positions, divided by the intensity measured at the offset positions. The observations were made with both polarizations and the average gain change is tabulated below. We assumed a 0.01 count uncertainty in each measurement.

Frequency   Offset-Azimuth              Offset-Elevation
  (GHz)     Average                      Average
   19       97.7 +/- 2.5 %               95.2 +/- 2.5 %
   25       99.4 +/- 4.4 %               89.4 +/- 4.5 %

The signal was weaker at 25 GHz, and the measurements were probably effected by the IF spurs in down conversion during the measurement.

-- GlenLangston - 08 Oct 2008