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) Secondary mirror 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 Position Switching to symmetrize the response.

UIP commands

  1. 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.
  2. 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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