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cso:instruments:heterodyne:onoff [2013-11-14 03:05] sradford created |
cso:instruments:heterodyne:onoff [2014-04-09 21:33] (current) sradford |
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+ | ====== Position 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). In position switching, the telescope points back and forth between the target and a nearby blank sky position. | ||
+ | |||
+ | ==== UIP commands ==== | ||
+ | |||
+ | - Position switching with reference positions 300 arcsec (5 arcmin) away in azimuth. \\ ''__uip__> **oo_scan //N// /step 300 /altaz** '' | ||
+ | * The telescope will move symmetrically \\ ''+OFF ON ON -OFF'' | ||
+ | * //N// is the number of repetitions of this pattern. | ||
+ | * Because the sky brightness does not change, moving in azimuth results in better subtraction. | ||
+ | - Position switching with reference position chosen to avoid emission regions, etc. \\ ''__uip__> **oo_scan //N// /designated_off ** '' | ||
+ | * The telescope will move asymmetrically \\ ''OFF ON'' | ||
+ | * //N// is the number of repetitions of this pattern. | ||
+ | * The reference position must be specified in the source [[cso:telescope:uip:catalog|catalog]] as //target//:off_position. | ||
+ | |||
+ | There are other possibilities. For details, consult the online help, \\ ''uip> ** help oo_scan ** '' | ||
+ | |||
+ | ==== Caveats ==== | ||
+ | |||
+ | * If the [[cso:telescope:secondary]] is wobbling, it will be stopped before an ''oo'' scan, then restarted. |