Tidbinbilla 70-m Radio Telescope Guide to Observations

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.

2006 2007 2008 2009 2010
2011 2012 2013 2014 2015

Click on the images for larger versions. These plots are also available in postscript formats: 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015.

Receivers

The following table lists the available receiving systems on the 70-m antenna.


Receiver

Band (cm)

Frequency Range (GHz)

Illuminated Diameter (m)

Beam FWHM (arcmin)

Tsys (K)

Peak Sensitivity (Jy/K) 
(a)

Polarisation

Instantaneous receiver bandwidth (MHz)

Status

L-band

18

1.610 - 1.705

70

8

25

0.9

LCP

95

available

S-band maser

13

2.270 - 2.300

70

6.4

16

~1

LCP or RCP (b)

30

available

S-band hempt

13

2.200 - 2.300

70

6.4

25

~1

LCP or RCP (b)

100

available

X-band

3

8.183 - 8.633

70

1.8

25

~1

LCP and/or RCP

100

available

K-band

1

18.0 - 26.5

70

0.8

40

1.5

LCP and/or RCP

400 (restricted frequencies)
70 (tunable)

available

(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:

  • 32 or 64 MHz bandwidth with up to 2 polarisation products of up to 2048 channels each
  • 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.
 


Configuration

No IFs

No Polarisations

Bandwidth (MHz)

No chans per band

das_xxxx_1_4096

2

1

 1

4096

das_xxxx_2_4096

2

1

2

4096

das_xxxx_4_4096

2

1

4

4096

das_xxxx_8_4096

2

1

8

4096

das_xxxx_16_4096

2

1

16

4096

das_xx_16_4096 

1

1

16

4096

das_xxyy_16_1024 

1

2

16

1024

das_xxyy_16_2048 

1

2

16

2048

das_xxyyxy_16_2048

1

2

16

2048

das_xxyy_16_4096

1

2

16

4096

das_xxxx_32_2048

2

1

32

2048

das_xxyy_32_2048

1

2

32

2048

das_xxxx_64_2048

2

1

64

2048

das_xxyy_64_2048

1

2

64

2048

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

Yanett Contreras is the ATNF Friend for Tidbinbilla. If you have any comments or questions regarding single-dish observations at Tidbinbilla, please email:

Yanett.Contreras [at] atnf.csiro.au


Observers
Public