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3. Receivers and Correlators

3.1 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:

$T_{rms} (mK) \sim {{T_{sys}} \over {\sqrt{npol {BW \over chan} \delta T}}}$

$S_{rms} ({mJy \over beam}) \sim T_{rms} G / \eta_b$

In the above, G is the main–beam gain (Jy/K) for a receiver defined from tab:rxprops, npol is the number of polarisations(1), BW is the bandwidth [MHz], nchan is the number of channels and $\delta T$ is the on-source integration time in seconds. $\eta_{b}$ is the beam efficiency factor: $\Omega_{mb} \over \Omega_{tot}$ = 0.7. For continuum, we need to calculate the sensitivity over the whole bandwidth. The continuum line brightness and line flux respectively become:

$T_{rms} (mK) \sim {{T_{sys} \over {\sqrt{npol BW \delta T}}}}$

$S_{rms} ({mJy \over beam}) \sim T_{rms} G / \eta_b$

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

3.2 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[a] Sens[b] Pols[c]  Bandw 
           [cm]     [GHz]      [m]    [']     [K]     [Jy/K]           [MHz]
----------------------------------------------------------------------------
1050cm      
            50     0.70-0.764  64     30     40        1.1?     2xL       64
            10     2.60-3.600  64     6.4    35        1.1      2xL     1000
MB20   
            21     1.23-1.53   64    14.2    28        1.1     26xL      300
H-OH         
            21/18  1.2-1.8     64    14.8    25        1.2      2xL      500
GALILEO      
            13     2.20-2.5    64     9.2    20        1.3      2xC      300
                   2.15-2.27   64     9.2?   20?       2.1?     2xC      120
                   2.29-2.3    64     9.2?   19?       1.4?     2xC       10
AT S-BAND[d]       
            13     2.2-2.5     64     9.2?   79?       1.9?     2xL      300
AT C-BAND[d]        
             6     4.5-5.1     64     4.5    50        1.3        C      500
AT X-BAND[d]        
             3     8.1.8.7     64     2.4   110        1.2    2xL|C      500
             3/13  8.1-8.7     64     2.4   110        1.2      2xL      500
                   2.2-2.5     64     9.2?   79?       1.9?       C      300
METH6     
                   5.9-6.8     64     3.4    55        1.4      2xC      300
MARS[e]       
             3     8.1-8.5     55     2.45   30        1.7      2xC      500
KU-BAND      
             2.2  12.0-15.0    64     1.9   150?       1.6?     2xL      500
13MM
             1.3  16.0-26.0    55    1-1.4   95        2.2      2xL     1000
                  21.0-22.3                                     2xC     1000
---------------------------------------------------------------------------
[a] Includes typical atmospheric, ground and galactic contribution at Zenith.
[b] Calculated over main-beam and using Omega_MB / Omega_A = 0.7.
[c] L = linear, C = circular, NB = narrowband.
[d] Dual linear feeds at S,C,X bands, lambda/4 plates avaliable for band centers.
[e] Full bandwidth by special arrangement.
A '?' indicates yet to be confirmed, use with caution.

Table 3.1: Parameters for the receiver fleet.

Most receivers 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.

For more information on particular receivers, please refer to individual links above in Table tab:rxprops.

3.3 Conversion System

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

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

3.4 Signal Path

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

JPEG/signalpath-overview

.

Figure 3.1: Overview of the Parkes observing system.

Single-beam spectral–line observations have back-end options using 4, 8, 16, 32, 64, ... MHz bandpass capabilities of the 8–bit digital filterbank, DFB4. For Pulsar observations, it is possible to switch simultaneously record data on several back ends at once.

3.5 Correlators

A number of correlators/backend units are available:

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

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Last updated by Stacy Mader on October 14, 2017