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Tidbinbilla 70-m Radio Telescope Guide to Observations
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Introduction
A limited amount of time is available on the 70-m antenna at the
Canberra
Deep Space Communication Complex (Tidbinbilla) for spectroscopy in
a service observing mode and other single-dish observations. Proposals
should be submitted to ATNF in the normal way for review by the Time Assignment
Committee (TAC). Proposals are prioritised according to the TAC rankings
with the highest priority sources observed first. Spectroscopy observations
will be conducted in service mode so the proposers are not required to
be present at Tidbinbilla although they may do so if desired. PIs are notified
by e-mail when their observations have been made and data are made available
either by FTP or on CD-ROM. Accepted proposals remain active for 12 months.
Proposals to use the 70-m antenna for purposes other than spectroscopy
may also be submitted however please
contact us
before applying to assess
the suitability of your proposal.
Time Allocation
As part of the Host Country agreement with NASA, a fraction of time on
the Tidbinbilla 70-m antenna is allocated for independent scientific activities
sponsored by the Australian Government. In the past this time has been
used mainly for VLBI observations but not all of it has been utilised,
either because it did not coincide with the availability of other LBA antennas
or because the period of the allocation was too short to provide useful
(u,v) coverage. It is this time together with surplus time allocated to
NASA spectroscopy projects that is being made available. Proposers should
bear in mind that the amount of available time is likely to be at the level
of 200 hours per year. If large amounts of time are required for a project,
please consider applying for time directly through the DSN (see
http://dsnra.jpl.nasa.gov/).
Typical allocations are 5 to 12 hrs in length with limited LST ranges.
Therefore projects that can be divided into observation periods of 1hr
or less are more likely to be observed than those requiring long integrations
on a single day.
Likely availability of the 70-m antenna
A high priority for the DSN is tracking spacecraft at Mars. Therefore
it is unlikely that much time will be available for radioastronomy while Mars
is above the horizon. The following figure shows when Mars is visible from
Tidbinbilla through the years 2005 to 2009 (shaded area). Local siderial time is indicated
by the diagonal lines and labeled at the top of the plots.
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2005
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2006
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2007
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2008
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2009
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2010
| 2011
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Click on the images for larger versions. These plots are also available
in postscript formats:
2005,
2006,
2007,
2008,
2009,
2010,
2011.
Receivers
The following table lists the available receiving systems on the 70-m antenna.
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Receiver
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Band (cm)
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Frequency Range (GHz)
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Illuminated Diameter (m)
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Beam FWHM (arcmin)
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Tsys (K)
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Peak Sensitivity (Jy/K)
(a)
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Polarisation
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Instantaneous receiver bandwidth (MHz)
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Status
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L-band
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18
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1.610 - 1.705
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70
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8
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25
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0.9
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LCP
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95
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available
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S-band maser
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13
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2.270 - 2.300
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70
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6.4
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16
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~1
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LCP or RCP (b)
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30
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available
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S-band hempt
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13
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2.200 - 2.300
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70
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6.4
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25
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~1
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LCP or RCP (b)
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100
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available
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X-band
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3
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8.183 - 8.633
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70
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1.8
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25
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~1
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LCP and/or RCP
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100
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available
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K-band
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1
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19.910 - 20.510
21.780 - 22.380
23.610 - 24.210
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70
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0.8
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40
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1.5
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LCP and/or RCP
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280
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available
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(a) With typical atmospheric contribution
(b) Dual circular polarisation S-band observations are possible with one polarisation through the hempt and the other through the maser.
Signal Path
Following down-conversion the signal from any receiver can be split, if
needed, and the centre frequency of those two IFs can be tuned independently.
For example, if high spectral resolution observations of both the 1665
and 1667 MHz OH transitions is required, the signal from the L-band receiver
can be split and the two IFs mixed so that IF1 is centred on the 1665 MHz
transition and IF2 is centred on the 1667 MHz transition. The correlator
could be configured to take 1 MHz bandwidth in each IF with 4096 chans
each.
The 1-cm (18.0 - 26.5 GHz) System
Sensitivity.
For a reference pointing observation, single polarisation:
RMS = 2.6E-3 * G(El) * Tsys / sqrt(W*t/N) Jy
where Tsys is in K (typically 40 to 50K),
W is total bandwidth in MHz
N is number of spectral channels
t is time on source in sec, and
G(El) is the antenna gain as a function of elevation
G(El) is described by the polynomial:
G(El) = R0 + R1*El + R2*(El^2)
where R0 = 3.58788e-1
R1 = 2.87243e-2
R2 = -3.219093e-4
The peak in the gain curve occurs at 44.6 degrees elevation and is
above 0.9 between elevations of 27 and 63 degrees.
Note the above equation does not include a correction for opacity
which in winter is typically 0.05.
There is now a
Sensitivity Calculator to help in planning observations.
Limitations at 1 cm.
Due to limitations in the working ranges of the amplifiers and down-converters
at 1 cm, it is necessary to reduce the 18 to 26.5 GHz band out of the LNAs
to ~600 MHz bandwidth. Below is a list of the available filters and their
frequency coverage:
Filter Frequency
coverage (GHz)
1
19.910 - 20.510
2
21.780 - 22.380
3
23.610 - 24.210
Following down-conversion the bandwidth is limited to 280 MHz to avoid
aliasing in the final mix. Therefore, if simultaneous observations of multiple
transitions is desired it is necessary that they be no more than 280 MHz
apart and within the same 600 MHz bandwidth filter. For example if observations
of both the (1,1) and (2,2) NH3 transitions at 23.694 and 23.722 GHz is
desired, the 600 MHz bandwidth filter number 3 would be selected and the
first local oscillator set so that 23.700 GHz is mixed to the centre of
the 280 MHz filter's range. The resulting signal would be split and the
two second LO's set so that IF 1 is centred on the (1,1) transition and
IF 2 on (2,2). The correlator could be configured to take 16 MHz bandwidth
in each IF with 4096 chans each.
Correlator
Tidbinbilla is equipped with an ATNF Multibeam correlator block capable
of:
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32 or 64 MHz bandwidth with up to 2 polarisation products of up to 2048
channels each
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16 MHz bandwidth or less with up to 4 polarisation products with a total
of 8192 channels (e.g. 2 x 4096 chans).
Available Correlator
Configurations
Below is a list of correlator configurations currently available. If the
configuration you want isn't listed, just
ask.
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Configuration
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No IFs
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No Polarisations
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Bandwidth (MHz)
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No chans per band
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das_xxxx_1_4096
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2
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1
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1
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4096
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das_xxxx_2_4096
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2
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1
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2
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4096
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das_xxxx_4_4096
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2
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1
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4
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4096
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das_xxxx_8_4096
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2
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1
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8
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4096
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das_xxxx_16_4096
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2
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1
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16
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4096
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das_xx_16_4096
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1
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1
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16
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4096
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das_xxyy_16_1024
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1
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2
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16
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1024
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das_xxyy_16_2048
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1
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2
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16
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2048
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das_xxyy_16_4096
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1
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2
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16
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4096
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das_xxxx_32_2048
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2
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1
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32
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2048
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das_xxyy_32_2048
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1
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2
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32
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2048
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das_xxyy_64_2048
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1
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2
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64
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2048
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| das_xx_16_8192 |
1 |
1 |
16 |
8192 |
Observation File Preparation
Once a proposal is approved, an observation file should be submitted
containing all the information necessary to conduct the observations. The file
should consist of one line per source with the fields separated by white
space. An example file is given in below. A web interface to assist in
observation file preparation is also available and is the reccommended
method.
Comments and Questions
Jimi Green is the ATNF Friend for Tidbinbilla. If you have any comments or questions regarding
single-dish observations at Tidbinbilla, please email:
James.Green [at] atnf.csiro.au
