next up previous contents
Next: Overheads Up: Example of calculation Previous: Applying the radiometer

Application of the formulae: one practical example

Assume that one wishes to detect with a S/N of 10 the CO(2-1) line from an extended envelope covering about the telescope main beam (). The expected line width and strengths are 6 MHz (7.8 km/s) and = 0.06 K (note that we assume in these crude calculations that we are still in the Rayleigh-Jeans regime). The line is assumed flat-topped.

We thus need theoretically to integrate during 1h 7h to reach the requested sensitivity. (If we wished to use the autocorrelator, this time would increase by a factor and would be 9 h.)

If we use the wobbling subreflector for these observations, the theoretical observing time will be 7h/R= 7/0.62= 11.3 h, to which we should add the receiver tuning (20min for 1 tuning, but one retuning after shifting the LO would be advised, so 30min) and the preparation steps (25min if this is the first observation).

Robert Lucas
Thu Mar 9 12:14:01 MET 1995