### WOBBLER SWITCHING

During WOBBLER SWITCHING the wobbling secondary mirror is switched between 2 positions, which are offset from the telescope axis by a fixed amount.

Thus there are 2 phases, and the signal is calculated as the difference between these 2 phases.

As the positions in both phases are offset from the telescope axis, in some observing modes, e.g, POINTING, FOCUS, ONOFF, the telescope position needs to be adjusted to compensate — this is done automatically.

WOBBLER SWITCHING is normally used with ONOFF or, for bolometer continuum mapping, with OTFMAP.

Note that for OTFMAP with WOBBLER SWITCHING, special restoration algorithms are needed to recover an image of the source brightness distribution. These are available, e. g., in the MOPSIC software.

If WOBBLER SWITCHING and ONOFF are combined in the standard way, we effectively take data at 3 positions: 1. the source position; 2. the source position + throw (offset in the “true-angle” horizontal system); 3. the source position - throw (offset in the “true-angle” horizontal system), with throw = ABS(wOffset2-wOffset1). Data from 1. are treated as source signal, data from 2. and 3. as off-source reference signal. Note that in the astronomical coordinates, positions 2. and 3. will rotate around the source position 1. Therefore one must normally be sure that the extent of the source is less than throw-beamWidth (/2).