====== Beam Switching ======

Single dish observations are explicitly differential: the signal from the On position (target+sky) is compared with the signal from the Off position (sky only). Beam switching is (usually) used for observations of compact sources. 
The wobbling (chopping) [[cso:telescope:secondary]] moves the secondary mirror to deflect the beam back and forth between the target and a nearby blank sky position. Beam switching is combined with [[onoff]] to symmetrize the response.

==== UIP commands ====

  - Start the secondary mirror \\ ''__UIP__> **secondary //throw// //frequency//** ''
    * //throw// is the the beam separation [arcsec]. 
    * For the switching //frequency// [Hz], avoid 1.00 Hz. Use an odd value instead, such as 0.534 Hz.
    * Tune the secondary mirror wobbler while the telescope is stationary or sidereal tracking.
    * Set the //PIDG// knobs to the suggested values.
  - Take a scan \\ ''__uip__> **chop //N//** ''
    * //N// is the number of repetitions.