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## 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:

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 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.

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.

## 3.3 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 8.1-8,7 GHz), spectral-line or broadband noise observations may be made simultaneously for each of the bands.
• ual 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 DFB4, BPSR and HIPSR, 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.

## 3.4 Signal Path

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

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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:

• DFB4: spectral-line, pulsar, continuum and polarimetry, for one IF dual polarization observations
• APSR: coherent dedispersion recorder for pulsar observations (one IF dual polarization).
• HIPSR: a new reconfigurable digital backend for the Parkes multibeam receiver with a maximum of 13 IFs, dual polarisation. HIPSR is capable of running many different firmware modes, so can be used for both high resolution, wide bandwidth spectral-line observations (see below), and high time resolution pulsar observations. As of writing, there is only one mode of operations supported: this is BPSR high time resolution pulsar modes, used in the HTRU survey. HISPEC is a 8192 channel, 400 MHz bandwidth spectrometer for H{\sc i observations and is currently not supported. Please contact Jimi Green for more information.

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