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cso:instruments:heterodyne:chop [2014-01-22 18:57]
cso:instruments:heterodyne:chop [2014-04-09 21:35] (current)
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 +====== 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. ​
cso/instruments/heterodyne/chop.txt · Last modified: 2014-04-09 21:35 by sradford
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