EMC Certification of a Digital Radio Astronomy Receiver: A Case Study

This paper outlines the challenge of practical EMC measurements on a large electronic system destined for a radio astronomy observatory. The digital receiver package of the Murchison Widefield Array (MWA) is used as a case study and progress towards meeting what is probably one of the world's most stringent EMC requirement is describe

Realisation of a low frequency SKA Precursor: The Murchison Widefield Array

The Murchison Widefield Array is a low frequency (80 - 300 MHz) SKA Precursor, comprising 128 aperture array elements distributed over an area of 3 km diameter. The MWA is located at the extraordinarily radio quiet Murchison Radioastronomy Observatory in the mid-west of Western Australia, the selected home for the Phase 1 and Phase 2 SKA low frequency arrays. The MWA science goals include: 1) detection of fluctuations in the brightness temperature of the diffuse redshifted 21 cm line of neutral hydrogen from the epoch of reionisation; 2) studies of Galactic and extragalactic processes based on deep, confusion-limited surveys of the full sky visible to the array; 3) time domain astrophysics through exploration of the variable radio sky; and 4) solar imaging and characterisation of the heliosphere and ionosphere via propagation effects on background radio source emission. This paper will focus on a brief discussion of the as-built MWA system, highlighting several novel characteristics of the instrument, and a brief progress report (as of June 2012) on the final construction phase. Practical completion of the MWA is expected in November 2012, with commissioning commencing from approximately August 2012 and operations commencing near mid 2013. A brief description of recent science results from the MWA prototype instrument is given

The low frequency receivers for SKA 1-low: Design and verification

The initial phase of the Square Kilometre Array (SKA) [1] is represented by a ~10% instrument and construction should start in 2018. SKA 1-Low, a sparse Aperture Array (AA) covering the frequency range 50 to 350 MHz, will be part of this. This instrument will consist of 512 stations, each hosting 256 antennas creating a total of 131,072 antennas. A first verification system towards SKA 1-Low, Aperture Array Verification System 1 (AAVSl), is being deployed and validated in 2017

Reducing the LUF of a reverberation chamber based on the concept of MIMO for electromagnetic emission measurements for radio astronomy applications

The International Centre for Radio Astronomy Research (ICRAR), a joint venture between Curtin University and The University of WA, is involved in a number of radio astronomy projects, and one of the tasks is the testing of equipment for Electromagnetic Compatibility (EMC). In order not to interfere with radio astronomy signals, electrical and electronic equipment close to, or at, radio astronomy sites must have a very low electromagnetic emission. Before an electronic device or system can be installed, it must be tested against stringent emission limits, and for that purpose it is crucial that the test facility has a very good sensitivity. To increase the sensitivity of the EMC measurements it is planned to convert an existing shielded room into a reverberation chamber. Reverberation chambers are in principle suitable for very sensitive emission measurements. However, they have limitations in respect to the frequency range; to test at low frequencies the chamber has to be big, so that the chamber can maintain the uniform field strength within the working volume. Instead of rotating a stirrer only, this paper studies the possibility to extend the usability of a reverberation chamber to lower frequencies by introducing the concept of multiple-input and multiple-output (MIMO) communication channels. This research project employs both measurements and computer simulation using a Finite Element Method (ANSOFT HFSS)

Radio interference evaluations of photovoltaic modules for radio astronomy active antenna

This paper presents a study on potential radio frequency (RF) emissions from photovoltaic (PV) modules, designed to power a typical low-frequency Square Kilometre Array (SKA) antenna element. Both conducted and radiated emissions were investigated to assess the impact of RF emissions on receiver sensitivity. The objective is to develop a method to screen PV modules at the component level. The method is correlated with measured results when a module is powering an antenna element to ensure that any emissions will not degrade receiver performance, while meeting SKA site requirements

EMC applications for military: Reverberation chamber tests

Electrical and electronic equipment installed on military platforms must have very low electromagnetic emission and good immunity for the whole operational frequency range. Reverberation Chambers (RC) are tools for sensitive emission measurements and immunity tests against strong electromagnetic fields, at a lower cost than other techniques. Method of RC should be suitable for testing Military's electronic devices such as radio or radar system. However, RCs must be large for tests at low frequencies; for example, at 80 MHz are conventional RC must have dimensions up to 7 m by 15 m by 8 m. For military concern, the lowest operation frequency can be as low as 2 MHz (underwater communication can be lower). Conventional RCs can only be used above a certain frequency, the lowest usable frequency (LUF), as they require a minimum mode density (number of modes per frequency interval) in order for the stirrer to perform effectively and alter field distributions. Technique of MIMO RC [1, 2] can make RCs usable down to much lower frequencies; it can mean the dimensions of the chamber can be up to 6 times smaller. However, the composite Q-factor of RCs can be rather low at low frequencies, and this affects the sensitivity, and ultimately usability of an RC. This paper studies the possibility to increase composite Q-factor when RC is used at lower frequencies than conventional method

BIGHORNS - Broadband Instrument for Global HydrOgen ReioNisation Signal

The redshifted 21cm line of neutral hydrogen (Hi), potentially observable at low radio frequencies (~50-200 MHz), should be a powerful probe of the physical conditions of the inter-galactic medium during Cosmic Dawn and the Epoch of Reionisation (EoR). The sky-averaged Hi signal is expected to be extremely weak (~100 mK) in comparison to the foreground of up to 104 K at the lowest frequencies of interest. The detection of such a weak signal requires an extremely stable, well characterised system and a good understanding of the foregrounds. Development of a nearly perfectly (~mK accuracy) calibrated total power radiometer system is essential for this type of experiment. We present the BIGHORNS (Broadband Instrument for Global HydrOgen ReioNisation Signal) experiment which was designed and built to detect the sky-averaged Hi signal from the EoR at low radio frequencies. The BIGHORNS system is a mobile total power radiometer, which can be deployed in any remote location in order to collect radio frequency interference (RFI) free data. The system was deployed in remote, radio quiet locations in Western Australia and low RFI sky data have been collected. We present a description of the system, its characteristics, details of data analysis, and calibration. We have identified multiple challenges to achieving the required measurement precision, which triggered two major improvements for the future system

The impact of the ionosphere on ground-based detection of the global Epoch of Reionisation signal

The redshifted 21cm line of neutral hydrogen (Hi), potentially observable at low radio frequencies (~50-200 MHz), is a promising probe of the physical conditions of the inter-galactic medium during Cosmic Dawn and the Epoch of Reionisation (EoR). The sky-averaged Hi signal is expected to be extremely weak (~100 mK) in comparison to the Galactic foreground emission (~10 4 K). Moreover, the sky-averaged spectra measured by ground-based instruments are affected by chromatic propagation effects (of the order of tens of Kelvins) originating in the ionosphere. We analyze data collected with the upgraded BIGHORNS system deployed at the Murchison Radio-astronomy Observatory to assess the significance of ionospheric effects (absorption, emission and refraction) on the detection of the global EoR signal. We measure some properties of the ionosphere, such as the electron temperature (T e ≈ 470 K at nighttime), magnitude, and variability of optical depth (τ 100MHz ≈ 0.01 and δτ≈ 0.005 at nighttime). According to the results of a statistical test applied on a large data sample, very long integrations lead to increased signal to noise even in the presence of ionospheric variability. This is further supported by the structure of the power spectrum of the sky temperature fluctuations, which has flicker noise characteristics at frequencies ≥10 −5 Hz, but becomes flat below ≈10 −5 Hz. We conclude that the stochastic error introduced by the chromatic ionospheric effects tends to zero in an average. Therefore, the ionospheric effects and fluctuations are not fundamental impediments preventing ground-based instruments from integrating down to the precision required by global EoR experiments