Flux density calibration

For amplitude calibration, the dual-frequency calibration procedure uses the flux density of the quasars which are stored in the data (header) file. The stored values may not necessarily be accurate, and usually require better determination. The FLUX button allows to switch to a different menu for better flux density scale calibration.

After selection of the receiver, a new window appears with the list of flux for the phase and amplitude calibrators of the project.

 

Figure 4: Interface for dual-frequency calibration

The window contains 4 command buttons:

• Solve which solves the unknown fluxes from sources with fixed flux.
• Get Result which accepts the solution from the last Solve
• Store which stores the accepted values into the data file.
• Plot which plots the efficiency curve as function of time.
• Calibrate which switches back to the main calibration procedure.

For each calibrator, 4 lines appear

• Input flux the value used as input for the Solve button.
• Fixed flux a logical variable indicating whether the Input flux value should be used as input, or not, by the Solve button
• Solved flux the flux determined by the last Solve action.
• Flux in file the flux stored in the data file.

The last two items are displayed for information, but cannot be modified directly by the user. They can only be modified through the Solve Get Result and Store buttons of the command window.

Once the user is satisfied with the Flux in file values, button Calibrate can be used to come back to the main calibration procedure.

Iteration for steps EFF. and AMPL. is usually required after adjustment of the calibrator flux densities. PRINT can be done at any time, although it is only essential for a final summary. PRINT gives a rather detail report, including phase noise, amplitude stability, estimate of seeing, etc.... However, these results are reset to unknown for each SELECT operation.