Keywords: pako

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### ONOFF

In its first form `ONOFF` is used with TOTAL POWER. Subscans are taken alternating between a position that's considered to be ``ON-source'' and a reference position that's normally assumed to be ``OFF-source'', i.e., free of emission.

The source signal is then calculated as the difference between ``ON'' and ``OFF''.

The basic parameters are the offsets for the ON position, parameters of the options are the offsets for the reference position, the (total) number of subscans, and the time per subscan in [s].

After you enter an ON-OFF setup manually, we recommend to ``save'' it, optionally to a named file:

`SAVE ONOFF [/FILE onoff-1]`

It can then at any later time be reloaded with `@ onoff[-1]`, see `HELP SAVE`.

You may want to save the switching mode seperately or with ONOFF into the same file:

    SAVE SWITCHING /FILE onoff-2
    SAVE ONOFF     /FILE onoff-2 /APPEND

When `ONOFF` is used with WOBBLER SWITCHING (command `SWWOBBLER`), the position offsets must be set to very specific values in TRUE (ANGLE) HORIZON depending on the parameters of `SWWOBBLER`. This is achieved by using the special option `/SWWOBBLER` of the command `ONOFF`.

Subscans are then taken alternating between 2 positions in such a way that: (a) in some subscans (one position of the antenna) the source is in the first of the two Wobbler phases, (b) in the other subscans (the other position of the antenna) the source is in the second of the two Wobbler phases. During the data processing, the source signal is computed as a double difference: 1st the difference of the 2 Wobbler phases; 2nd the difference between `ONOFF` subscans (a) and (b).

This form of `ONOFF` is also called ``Wobbler-Onoff'' or sometimes simply ``Wobbler Switching''.

The combination(!) of `ONOFF` and WOBBLER SWITCHING provides a very high sensitivity in continuum bolometer observations of compact sources, and excellent baselines for spectroscopy.

It has the disadvantage that the (emission-free?) off-source positions are very close to the source (limited by the maximum Wobbler throw). Also, the Wobbler direction is fixed in the horizontal system relative to the telescope, and therefore in the source system the off-source positions rotate around the source position.

For continumm observations, usually a short time per Wobbler phase, s, is used with small Wobbler offsets (throws); for spectroscopy, largest possible Wobbler offsets (throws), up to are preferred, but then the time per phase must be longer, - s.

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