A 'pulsar timing array' (PTA), in which observations of a large sample of pulsars spread across the celestial sphere are combined, allows investigation of 'global' phenomena such as a background of gravitational waves or instabilities in atomic timescales that produce correlated timing residuals in the pulsars of the array. The Parkes Pulsar Timing Array (PPTA) is an implementation of the PTA concept based on observations with the Parkes 64-m radio telescope. A sample of 20 ms pulsars is being observed at three radio-frequency bands, 50 cm (ß700 MHz), 20 cm (ß1400 MHz), and 10 cm (ß3100 MHz), with observations at intervals of two to three weeks. Regular observations commenced in early 2005. This paper describes the systems used for the PPTA observations and data processing, including calibration and timing analysis. The strategy behind the choice of pulsars, observing parameters, and analysis methods is discussed. Results are presented for PPTA data in the three bands taken between 2005 March and 2011 March. For 10 of the 20 pulsars, rms timing residuals are less than 1 μs for the best band after fitting for pulse frequency and its first time derivative. Significant 'red' timing noise is detected in about half of the sample. We discuss the implications of these results on future projects including the International Pulsar Timing Array and a PTA based on the Square Kilometre Array. We also present an 'extended PPTA' data set that combines PPTA data with earlier Parkes timing data for these pulsars.

Here, we describe the Compact Array Broad‐band Backend (CABB) and present first results obtained with the upgraded Australia Telescope Compact Array (ATCA). The 16‐fold increase in observing bandwidth, from 2 × 128 to 2 × 2048 MHz, high‐bit sampling and the addition of 16 zoom windows (each divided into further 2048 channels) provide major improvements for all ATCA observations. The benefits of the new system are: (1) hugely increased radio continuum and polarization sensitivity as well as image fidelity; (2) substantially improved capability to search for and map emission and absorption lines over large velocity ranges; (3) simultaneous multi‐line and continuum observations; (4) increased sensitivity, survey speed and dynamic range due to high‐bit sampling and (5) high‐velocity resolution, while maintaining full polarization output. The new CABB system encourages all observers to make use of both spectral line and continuum data to achieve their full potential. Given the dramatic increase of the ATCA capabilities in all bands (ranging from 1.1 to 105 GHz) CABB enables scientific projects that were not feasible before the upgrade, such as simultaneous observations of multiple spectral lines, on‐the‐fly mapping, fast follow‐up of radio transients (e.g. the radio afterglow of new supernovae) and maser observation at high‐velocity resolution and full polarization. The first science results presented here include wide‐band spectra, high dynamic‐range images and polarization measurements, highlighting the increased capability and discovery potential of the ATCA.

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