Switching Modes

  The DAS can be used in all the normal switching modes ( PSSW, BMSW, FSW, NSW, USW).

To change between Fast Frequency Switching ( FSW - only available with RxB3i) and Secondary chopping ( BMSW), the switches on the box above the AOSC in the computer room must be set correctly. This applies to both the DAS and the AOSC. In Frequency switch mode, the DAS requires a blanking signal, which is generated by this box. It is currently set to 50 msec blanking. In beamswitch mode, the Secondary mirror can generate the blanking, although this is currently disabled, and the internal blanking from this box is used. The maximum beamswitch rate should be small enough that the SMU blanking period is much less than the time at each beam, in order to minimise overheads; 1Hz is a good compromise between overheads and baseline stability. The LED's on this box show the blanking and BMSW/FSW rate.

For Fast Freq Switch (ie using RxB3i), the switches should be set to FREQ SWITCH and INTernal BLANK. For Beam Switching, set them to SMU REF and INTernal BLANK (and normally this is the mode they should be left in).