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%META:TOPICINFO{author="NicoleRadziwill" date="1088002380" format="1.0" version="1.1"}%
GBT Standard Observing Mode 5
Return to Standard Observing Modes
Purpose: To take spectra of compact sources with modest or weak continuum emission, at frequencies of Ku-band and higher.
Example Application: H2O masers, formaldehyde observations
Description: Beam switching is an observing mode whereby a
chopper alternates the position observed on the sky at some rapid rate, say
1 Hz, in order to remove atmospheric fluctuation. Beam switching can be
useful for observations above 10 GHz. The switch can be a mechanical device
that nods a subreflector or tertiary mirror, or it can be an electronic switch
that alternates the signal received by two feeds in a multifeed receiver
through two IF paths. For the GBT, only electronic beam switching is
available, and it is used in the Ku-, K-, and Q-band receivers. Because of
the arrangement of the electronic beam switch, many observers may choose to
use total power nod observations with equally good, or better, results.
Example Configuration File:
from gbtsetup import *
g = gbtsetup()
g.receiver = 'Rcvr18_22'
g.beam = 'B12'
g.obstype = 'Spectroscopy'
g.backend = 'Spectrometer'
g.nwin = 2
g.restfreq = 22235.08, 22235.08
g.deltafreq = 0, -180
g.bandwidth = 200
g.swmode = "sp"
g.swtype = "bsw"
g.swper = 1.0
g.swfreq = 0.0, 0.0
g.tint = 30
g.vlow = 0
g.vhigh = 0
g.vframe = "bary"
g.vdef = "Optical"
g.noisecal = "lo"
g.pol = "Circular"
g.nchan = "high"
g.setup()
Configuration cases of interest: C17,
C20
More Information About Receivers
Procedure: Identical to dual beam total power observations. |