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cso:instruments:heterodyne:chop [2014-01-22 18:57] sradford |
cso:instruments:heterodyne:chop [2014-04-09 21:35] (current) sradford |
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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. | ||
