RadioImaging

From ElecWeb

Radio Imaging Research Consortium

This New Zealand wide collaboration involves the development of new instruments to map the radio sky. Principle Researchers:

• Victoria University, (Dr Melanie Johnston-Hollitt, Dr Chris Hollitt.)
• University of Otago, (Dr Tim Molteno, Assoc Prof Colin Fox, Mr. Patrick Suggate, Mr Ian Scott)
• Auckland University of Technology. (Dr Slava Kitaeff, Mr. Achala Perera, Mr Dave Crofts)

We have been developing Transient Radio Events Sensor Network for deployment in New Zealand since 2006. This sensor network will allow us to register, map and possibly image transient radio events at 15-20 MHz frequency band. The most essential part of this network is a comprehensive electronic device Digital Receiver Sensor (DRS) has been developed at Center for Reconfigurable Systems of AUT.

Inaugural meeting of the SKA Research Consortium will be held on the 18th June.

Overview

We live in the ocean of electromagnetic waves (EMW) of manmade and natural origin. While manmade EMW have a predefined nature, EMW of natural origin carry important information about local and global environments. Many natural origins of EMW have been detected and studied at all ranges of electromagnetic spectrum, from radio up to Υ-rays. Most of detected and then studied EMW signals have either continuous, repetitive, or of predictable time patterns. The techniques developed to detect such EMW are also selective in time, as well as in frequencies and space. This means that those EMW phenomena which could be originating short or/and seldom irregular bursts of electromagnetic radiation are still undetected and unidentified, and so remain unstudied, or poorly comprehended. Such events have been dubbed transient and are considered as an important source of new science. While an unlimited search in the time, space and frequency domains will remain unfeasible for some time yet, some work can already be undertaken, thanks to digital technologies.

Device Development

Figure 1. DRS Mark I prototype.

Digital Radio Sensor (DRS) device in its essence is a dual-channel direct sampling digital receiver. It carries high accuracy GPS and thermally stabilized oscillator what allows synchronization multiple independent DRSs and time-stamping the data with the accuracy up to 25 ns. The device is equipped with 1Gb Ethernet interface for uploading data, full speed USB 2 interface for connecting to a PC or external HDD, and SD card interface for buffering data in a flash memory. The “hart” of DRS is Altera’s Cyclone III FPGA device, which provides pre-processing and packaging the data. DRS has the capability to carry plug-in sensor devices such as environmental sensors. DRS has been designed as a modular device, so RF part is separate from digital. ADC allows IF sampling up to 400 MHz if necessary for down conversion. Current RF module design id three-stage variable gain low noise amplifier and filter providing the frequency band 15-20MHz. Additional low noise pre-amplifier module has been designed for the cases when DRS can not be installed sufficiently close to the antenna. Three-stage amplification provides up to 120 dB gain in total. The antenna can have one of two configurations: a) cross-polarized broadband active dipole or b) two-element interferometer. Figure 1 features Mark I prototype. Mark II prototype is expected to be ready for testing in July 2009.

High Performance Computing

Signal Processing for the Transient Radio Events Sensor Network is done digitally inside the FPGA. Further collection of the data and post-processing of the data requires high performance computing facilities.

Site Selection

A preliminary survey of sites for radio-frequency interference (RFI) has been carried out. Based on this survey some promising areas have been identified. The South Island of New Zealand is blessed with wonderful radio-quiet sites far from any large urban areas and protected by the natural landscape. Considerable work has been done already and promising sites have been identified in the Mackenzie Country as well as other remote regions of South Island.