On 26aug00 an sband transmit experiment ended at
3:00 hours. The temperature in the rotary floor room had risen from 74
degF to 82 degF. The air conditioning in the room got the temperature back
down to 74 degF at 6:00 hours. The outside air temperature was about 73
At 4:00 hours a calibration run at cband was started on J0318+164 doing position switching. 1 minute on,offs were done with a 1 minute move between the positions. The cal was fired for 10 seconds on/off at the end of each off position. The scale factor to convert from correlator counts to Kelvins was computed every 3 minutes from the cal data (cal[K])/(calOn-calOff[corCnt]). Since the attenuators were not changed during the run, this value should be a constant unless the gain or the size of the cal changed. The data showed a large drift in this value over the entire run. The system temperature measurements using the cal showed no long term drift which implies that the drift was in the gain and not in the calValue itself (the cal diodes are also temperature stabilized.
When calibrating spectra, we assume that the cal scale factor is constant for the integration. Assuming the cal is not changing, then the error in the calibration is the change in the cal scale factor over the integration (or maybe 1/2 that). In our case for 1 minute on /offs it ranges from 0 to 2%. Most position switching is 5 minutes on/off. This would last for 4 of the 1 minute measurements. Even during a normal observation (without an sband xmit experiment) you could get a 2% change over a 5 minute on/off.
We are only measuring the air temperature in the rotary floor room. There is also gain downstairs. The temperatures of the devices that are affecting the gain can change at a different rate than the air temperature (they probably change more slowly). A small part of the change can come from the za change during the cal on/off.
processing: x101/cb/aug00/26aug00.pro and then tempstab.pro