NRAO Home  >  Green Bank  |  Wiki Topic:    GB > Data > PlanOfRecordC42004 > StandardObservingModes > HowToReduceMultiIFData

Changes | Index | Contents | Search | Statistics | Jump to Topic

Multi-IF Data Reduction Considerations

Observers can choose to record more than one frequency band simultaneously. This is referred to as Multi-IF observing. For example, one may observe HI (1.420 GHz) and OH (1.665 GHz) toward the same source simultaneously, recording say a 12.5 MHz spectrum for each IF path.

With Multi-IF observing, the telescope configuration (e.g. switching scheme and backend configuration) is usually the same for each IF, and so the data reduction process is trivial. Simply follow the directions for single-IF observing for each of the IF recordings in the Multi-IF configuration. Typically the procedure for calibration will be identical for each IF observed. Analysis may differ for each IF, depending on the science goals.

It is conceivable to configure with a multi-IF setup and send each IF signal into a different backend. For example, IF 1 may be recording a 12.5 MHz spectrum in the ACS and IF 2 may be recording the continuum using the DCR. In this case, each IF is reduced independently, according to the procedures outlined in the Data Reduction Cases.

Some observers may configure a multi-IF setup such that each IF is recorded by the same backend, centered at the same frequency, and observing the same range of frequencies. There is little advantage in doing this if the goal is to improve signal-to-noise ratio. The only improvement in signal-to-noise will come from averaging out the small noise introduced by the recording equipment. It may be advantageous to use such a setup if one or both of the IF paths are affected by spurious problems, such as bad channels. In this case, the data reduction process may have an additional step, after calibration, to combine the multi-IF recordings into a single spectrum, with the bad channels removed.

-- JimBraatz - 30 Jul 2004