2. Planning Your Observations

2.1 Applying for Observing Time

Proposal forms and submission deadlines can be found here, while current and archived observing schedules can be found here.

Information regarding system capabilities not listed here can be addressed to parkes-operations@csiro.au

2.2 Radio-Frequency Interference Considerations

An introduction to RFI observed at the observatory and surveys performed is available here.

2.3 Observing Modes

Spectral and continuum-line observations can be performed with all currently-available receivers and back-ends. Possible observing modes include:

• TRACK: Simply track the position for the specified length of time.
• SCAN: The telescope scans from one end to the other at a requested rate.
• MX: The position is tracked in turn by each beam (Multibeam receivers only.)
• MXCAL: Observe a calibrator with each beam in turn (Multibeam receivers only.)
• SPOT: Scan across a source for the purposes of defining pointing offsets and calibration parameters.
• Equatorial-Horizontal Mixed Scans: Here the telescope can perform AZ-EL "spider" scans (..., -90, -45, 0, 45, 90, ...) referenced to an RA/DEC position. The scans are conducted along the Great Circle passing through the source. Mapping an area in AZ-EL centred on the RA/DEC position is also possible.

There are three methods of switching. Not all methods are available with all receivers/back-ends.

• Position Switching: Using the TRACK mode, the telescope alternates between an on and off-source position where the latter is assumed to be free of line emission. This mode is typically used for observing molecular lines such as Ammonia and Maser lines. Point-by-point mapping can be done with this mode.
• Frequency Switching: During an observation, the observing frequency alternates between a pair of frequencies. Both slow and fast modes are available. This mode is often used for SCANNING on-the-fly observations which look at spatially-extended emission such as wide (Galactic HI) and narrow hydrogen recombination spectral lines. The second (switched) frequency is used as a reference spectrum which aids in data reduction and can increase signal to noise by at least a factor of two over the position-switching mode. The total frequency switch can be either “in-band” or “out-of-band”. The size of the throw depends on the nature of the emission you are seeking. The throw should be at least 2-3 times the width of the widest profile you might expect in your data. You should also be aware if you are observing multiple spectral lines within a bandpass, some of the data processing applications such as LIVEDATA produce ghosts which may overlap and be confused with real spectra. For estimating the size of the required throw, for wide Galactic HI observations, a frequency throw of about 3 MHz with an 8 MHz bandwidth is the norm.
• Beam Switching This is currently restricted to Multibeam receivers (MX mode). The position is tracked in turn by each required beam of the Multibeam system. This mode is ideal for observing sources such as single galaxies (or multiple if all lie within the beam). When a beam is not looking at the source we assume it’s collecting a reference spectrum from blank sky. The prior and following scans are used to form the bandpass calibration.

2.4 Preparing Schedule Files

For the majority of programs, you will be using the Telescope Control Software (TCS). The TCS graphical user interface (TCS GUI) is written in Glish/Tk and runs on a Solaris workstation. A glish client runs on the same host as the TCS GUI which serves as a communications channel between the TCS GUI and the (Linux) controller.

There are two ways to use TCS. The first is to select observing parameters from the TCS GUI via widgets and entry boxes. The second (and recommended) is to use schedule files which are loaded values become the default parameters on the TCS GUI. Until accustomed with the system, first-time users are strongly urged to use schedule files. Detailed information on keywords used in schedule files and examples can be found in the TCS documentation

Some of the main items to worry about in your schedule file(s) are as follows, but note this is not an exhaustive list!

• Project I.D.: PXXX (i.e. your project code)
• Project Name: as desired
• Correlator configuration, i.e., DFB3 "sdfb3_256_8192" for a spectral mode 256 MHz BW and 8192 channels or "sdfb3_tb16_64_512" for a time-binning mode 16-bins, 64 MHz BW and 512 channels
• receiver: your receiver
• Cycle time: e.g. 8 [sec]
• Time bins: 1 (spectral mode); number of time bins (time-binning). E.g. 16
• Doppler tracking
• feed angle: normally 0.0 (from -90 to 90)
• Parallactic angle tracking: ENABLED/DISABLED
• Frequency: central frequency
• Bandwidth [MHz]
• #channels
• Polarization products: some examples: 2 => for spectral mode, total intensity only. 3 => for full Stokes parameters (typically in time-binning).
• frequency switching: SIGNAL (no freq sw), SLOW (for freq sw) then set the frequency offset [MHz]
• Tsys recording: add "enable becc" to your schedule (or type it in the TCS "Command" field).

There are online utilities to assist in the preparation of schedules for position–switching, beam–switching, tracking (with or without frequency switching) and on-the-fly mapping. These can be found on the Parkes utilities page. Note that these tools DO NOT cater for Pulsar observations.

2.5 Sensitivity

When preparing your observing proposal, you are required to estimate the expected brightness and sensitivity of your source for your particular Correlator/receiver combinations. For spectral-line observations, sensitivity per bandwidth channel can be estimated from the following equations of line brightness and line flux respectively:

In the above, G is the gain (Jy/K) for a receiver defined from tab:rxprops, npol is the number of polarisations(2), BW is the bandwidth [MHz], nchan is the number of channels and is the on-source integration time in seconds. is the beam efficiency factor: = 0.7. For continuum, we need to calculate the sensitivity over the whole bandwidth. The continuum line brightness and line flux respectively become:

For both the line and continuum flux, the source is assumed to fill the main beam which has efficiency = 0.7. 1-sigma theoretical RMS noise estimates for line and continuum observations can be estimated by using the on-line Sensitivity Calculator.

2.6 Parkes Receiver Fleet

Click on the receiver links below in tab:rxprops to show information regarding receiver information such as characterization tests, gain-elevation curves and pointing accuracy. Please note this information is being uploaded when receivers are installed and may not be available at the present time.

----------------------------------------------------------------------------
Receiver   Band     Range   Diameter  FWHP    Tsys  Sen[a]    Pols[b]  Bandw 
           [cm]     [GHz]      [m]    [']     [K]   [Jy/K]             [MHz]
----------------------------------------------------------------------------
70cm         
            70     0.44        64    30      65       2       2xL       36
1050cm      
            50     0.70-0.764  64    30      40      1.7?     2xL       64
            10     2.60-3.600  64     7      30      1.5?     2xL     1000
MB20   
            21     1.23-1.53   64    14      23.5    1.5     26xL      300
H-OH         
            21/18  1.2-1.8     64    14      25.5      1.3    2xL      500
Galileo      
            13     2.20-2.5    64     9.2    20      1.9      2xC      300
                   2.15-2.27   64     9.2    20      1.9      2xC      120
                   2.29-2.3    64     9.2    19      1.4      2xC       10
AT S-BAND[c]       
            13     2.2-2.5     64     9.2    79      1.9      2xL      300
AT C-BAND[c]        
             6     4.5-5.1     64     4.2    50      2.2        C      500
AT X-BAND[c]        
             3     8.1.8.7     64     2.7    54      2.1    2xL|C      500
             3/13  8.1-8.7     64     2.4    60      2.1      2xL      500
                   2.2-2.5     64     9.2   100      2.0        C      300
METH6     
                   5.9-6.3     64     3.3    50      2.2      2xC      300
                   6.4-6.8     64     3.3    50      2.2      2xC      300
METH12
             2.5 12.0-12.4     64     2.0    50      3.5      2xC      250
Mars[d]       
             3     8.0-8.9     64     2.45   25      1.7      2xC      500
13MM[e]       
             1.3  16.0-26.0    55    1-1.4   60      4.5      2xL     1000
                  21.0-22.3                                   2xC     1000
KU-BAND      
             2.2  12.0-15.0    64     1.3   140      5.8      2xL      500
K-BAND    
             1.3  21.0-24.0    55     1.5   105      3.5      2xC      500
---------------------------------------------------------------------------
[a] Calculated with typical atmospheric contribution.
[b] L = linear, C = circular, NB = narrowband.
[c] Dual linear feeds at S,C,X bands, /4 plates avaliable for band centers.
[d] Full bandwidth by special arrangement.
[e] See section on this receiver below.

Table 2.1: Parameters for the Parkes receiver fleet.

2.6.1 Receiver Calibration Signal

Most of the Parkes receivers including allow injection of a calibration noise signal into the receiver waveguide ahead of the ortho-mode transducer (OMT). This is generally a more satisfactory method than injecting after the OMT or after the LNAs as these elements can then be modelled using the calibration signal.

The calibration signal is generally injected through a coupler in the circular waveguide oriented at 45 degrees to the linear probes of the OMT. Thus the cal can be closely represented by a 100% linearly-polarised signal with an accurately known feed angle.

The amplitude of the cal signal is adjustable by inserting or removing fixed attenuators between the noise source and the coupler. Changing the level requires access to the receiver in the focus cabin and takes of order 30 minutes. The cal can be switched on or off remotely as required, using an observer-selectable waveform. Typically the cal is run as a continuous low-level NAR (Noise-Adding Radiometer) with the cal level approximately 10% of Tsys, for a time-averaged increase of 5%. The frequency of the switching signal is typically between a few Hz and 500Hz.

The H-OH receiver has an optional quarter-wave plate which can be inserted in the circular waveguide between the feedhorn and the OMT to achieve circular polarisation on the sky. The quarter-wave plate is inserted before the cal injection so in this case the cal signal resembles a 100% circularly-polarised signal on the sky but the cal signal alone cannot be used to model the precise properties of the quarter-wave plate.

The 13MM receiver also has an optional quarter-wave plate used with the narrow-band VLBI feed covering the 22 GHz water transition. As with the H-OH receiver, the cal injection occurs after the polariser (between the polariser and the OMT).

The MARS (8.4 GHz; X–band) receiver has a built-in (non-removable) waveguide circular polariser also with cal injection between the polariser and OMT.

The C-band and X-band receivers in the AT Multi-band receivers also have quarter-wave plates ahead of the cal injection.

The GALILEO receiver has cal injection into circular waveguide but uses a circularly-polarised OMT (cal signal resembles 100% linear on sky).

The 50cm receiver in the 1050CM package injects a cal signal using a directional coupler after each LNA (strictly, after the 4-port hybrid used to combine the signal from each pair of opposing probes and LNAs). A splitter is used to generate two identical cal signals from the same noise source.

2.7 Conversion System

The Parkes Conversion System (PCS) is summarised as follows:

• It is possible to observe simultaneously two widely separated spectral line features within a receiver passband. Alternatively, in the case of a dual band receiver (eg. The S-X receiver covering 2.2-2.5 GHz and 8.0-9.2 GHz), spectral line or broadband noise observations may be made simultaneously for each of the bands.
• Dual polarisation is available for each of the observing frequencies, necessitating a total of four conversion channels. However, as the modules are paired, only two independent Local Oscillator (LO) systems are needed.
• The input bands are 300-750 MHz (UHF-band), 1.2-1.8 GHz (L-band), 2.2-3.6 GHz (S-band), and 4.5-6.1 GHz (C-band). Observations outside these bands, for example at K-band (22 GHz) are accommodated using an extra conversion on the receiver package or using LOs in the focus cabin and/or upstairs control room.
• Wherever possible signals generated by the local oscillator system should not fall within any signal or intermediate frequency (IF) bands to reduce the incidence of internally generated interference [2]. Unfortunately, due to the very wide S-band (2.2-3.6 GHz), one of the LO frequencies may fall inside the band for some observing frequencies.
• Frequency switching may be used for observations of a single spectral line. For C-band inputs, frequency switching is available for two spectral lines simultaneously.
• In order to ensure the conversion system is capable of supporting simultaneous use of Digital Filter Banks, Multibeam Correlator, BPSR, APSR, Pulsar Analogue Filter Banks, and CASPSR, a number of buffered outputs for each output bandwidth have been provided. Each of the 4 channels has 4 of 64 MHz, 3 of 128 MHz, 3 of 256 MHz, and 2 of 900 MHz bandwidth (BW) outputs available. One complete set of outputs for each channel (64, 128, 256, and 900 MHz BW) have been provided at the front of the conversion rack. The remaining system outputs are cabled to bulkhead connectors in the rear of the rack for permanent connection to the DAS and an RF Switch Matrix. The latter operates the standard connections from the conversion system to the several correlators/backend units. It is operated by software and in most cases the connection Conversion System output to backend is automatically instated by the observation control software (TCS: Telescope Control System).

An in–depth discussion of the PCS (including block diagrams) is available here.

2.8 Signal Path

An overall outline of the Parkes observing system is shown in fig:signalpath-overview.

.

Figure 2.1: Overview of the Parkes observing system.

Single-beam spectral–line observations have back-end options using 4, 8 or 64 MHz bandpass capabilities of the 2–bit Multibeam correlator, or patching in an ATCA–style bandpass filter to provide 16 or 32 MHz bandpass capability. Wider bandwidths (>64 MHz) are available using the 8–bit Digital Filterbanks (DFB3/DFB4), but it is also possible to achieve smaller bandpasses with DFB3/DFB4 (ie., 8, 16, 32 MHz).

For Pulsar observations, it is possible to switch simultaneously record data on several back ends at once.

2.9 Standing Wave Reduction

For Parkes, characteristic small-scale ripple with periodicity 5.7 MHz arises from multiple reflections in the 26m space between the vertex at one end, and the focus and/or underside of the focus cabin at the other. fig:standwave shows 22 GHz observations of a strong Ammonia source, G316.819, showing strong (1,1) and (2,2) transitions for 4 minutes (exact multiple of 60 seconds). The two observations were taken one after the other, the first (upper panel) with no special ’de-rippling’ measures, the lower taken in a mode where the receiver is moved cyclically up and down in the translator Y-axis to ’smear out’ the ripple with amplitude 6.3mm peak-to-peak (/2) and period 60 seconds. This technique is available for use with higher-frequency receivers only and proposers should contact Parkes Operations (parkes-operations@csiro.au) before submitting proposals.

Figure 2.2: Upper panel showing characteristic 5.7 MHz standing wave interference

with lower panel showing a cleaner spectrum obtained with receiver cycling.

2.10 Correlators

A number of correlators/backend units are available:

• DFB3: spectral line, pulsar, continuum and polarimetry, for up to two IFs dual polarization observations
• DFB4: spectral line, pulsar, continuum and polarimetry, for one IF dual polarization observations
• Multibeam Correlator: multi beam correlator for spectral line observations for up to 14 IFs dual polarization.
• BPSR: multi beam digital backend for pulsar observations (up to 13 IFs dual polarization).
• APSR: coherent dedispersion recorder for pulsar observations (one IF dual polarization).
• AFB: Analogue Filter Banks, analogue multibeam backend for pulsar observations (up to 13 IFs).

Please check the Parkes Correlator Guide for information on capabilities or email parkes-operations@csiro.au to ascertain requirements.

2.11 Dish Surface Quality

A 4 GHz holographic survey of the dish surface was performed prior to the 1995 upgrade of the focus cabin. Other surveys at 3.95 GHz (June 1996) and 12.75 GHz (July 1996) were performed after the installation of the new focus cabin. Details of the readjustment of the inner 44m of the Parkes reflector in December 1996 is also also available here. As part of the NASA Mars tracking contract in 2003/2004, the Parkes Telescope’s surface was upgraded to make it more reflective and sensitive at X-band ( 8.5 GHz). The surface upgrade improved the telescope’s performance by about 1 dB (or 25%). A technical guide is available.

This document was generated by Stacy Mader on October 13, 2011 using texi2html 1.82.