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
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.
- 08 Oct 2008