Good Calibration Practices
Typically the standard GBT calibration is good to 10-15%. This increases to 20-30% above 65 GHz. It is possible to achieve better calibration following the suggestions below.
The KFPA receiver has variable noise diodes. It is thus mandatory that all KFPA observations perform a calibration check for each observing epoch so that all of the data can be calibrated on the same flux scale since the noise diode values can change from one epoch to the next.
For best flux density calibration of spectra, it is recommended that you should observe continuum flux density calibration sources at least once during an observing session. To do this, do a Peak/Focus on the calibrator, followed by an observation in the same spectral line setup used for the program sources. This will give the relation of flux density to antenna temperature as a function of frequency that can be applied to the program spectra. If you can observe a calibrator both at the beginning and end of a session, it will also indicate if there have been any changes in the GBT system which need to be taken into account during the observing run. Of course, there may be other outstanding reasons to perform calibration observations more often. If you have concerns over how often you should observe a calibrator you should get into contact with your GBT support person.
