Pulsar Radio Observations using Software Defined ...

Pulsar Radio Observations using Software Defined Radio Gancio G.M. {1}, Tueros M. {1}, East P.W. {2} 1-Instituto Argentino de Radioastronomía CCT La Plata - CONICET, Buenos Aires, Argentina. 2-British Astronomical Association, Burlington House, London, United Kingdom.

Project Description

Introduction

Using the new digital receiver at IAR1 {1}, based on Software Defined Radio (SDR) technology, we developed a new receiver software for the detection and measurement of pulsars.

To acquire signals from the radio telescope, two SDR receivers were installed in the control room of the radio telescope. ➢ Pulsars observed at 1413MHz with 2MHz Bandwidth. ➢ Up to 100 minutes Observations. ➢ Two SDR for Dispersion Measurements. ➢ SDR at 150MHz Intermediate Frequency. ➢ SDR Clock Synchronization with Time&Frequency GPS Time Base. ➢ Personal Computer for control and Acquisition. Front-End receiver Basic Diagram Linear Polarization

IAR SDR-RTL receiver Vela Pulsar Image (Wikipedia)

Filter Select HI Cryo LNA OH At room Temp

Mixer

SDR systems are radio devices in which components typically implemented on hardware (such as mixers, filters, etc) are implemented in software using a personal computer or embedded computing devices. Unlike a conventional receiver, SDR systems have a reduced RF input stage followed by a fast digital conversion, and the signal is processing is done in software.

Resulting Observations Vela Pulsar (PSR B0833-45 / PSR J0835-4510) ● Rotation speed of 89 milliseconds. ● Located at a distance of 936 years. ● Average intensity 1100mJy. ● Dispersion Measurement of 67.99.

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Noise Injection Calibration

150MHz

LNA Power splitter

Amplitude [relative] .04 .0405 .041 .0415 .042 .0425

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50

100

150 200 Sample [n]

250

150MHz I.F. x2 From Front-End

AMP 150MHz

Local Oscillator O.L From Back-End 1.5GHz I.F. AMP To Back End

Second Polarization

Power Splitter

Control Room Back-End receiver Basic Diagram

SDR RTL2832u x2

Adquisition Computer 1.5GHz O.L. To Front End

X48 RF Multiplier

DDS signal generetor. SDR: Out 28,8MHz O.L.: Out 32,xxxMHz

Disciplined GPS 10MHz Out

Back End Block Diagram

Front End Block Diagram

Software Description The detection of pulsars was performed using the technique of "folding" in which once known the period or frequency of the Pulsar the acquired data is "folded" and averaged in time series, in order to eliminate noise and leave only the signal of interest. The programs involved are: ● Python Script that provides the interface with TEMPO program to know the adjusted value of the period of a pulsar for a certain date. ● Custom Application to process the raw files and "folding" the data, based on already known pulsar period. ● Application to convert the raw format files files into ".fil format" to be processed with the PRESTO tool-chain, (PulsaR Exploration and Search Toolkit) developed by Scott Ransom from NRAO.

Pulsar PSR J0437-4715 ● Discovered by the Parkes Observatory in Australia. ● Rotation speed of 5.75 milliseconds. ● Estimated to be at 509.8 light years. ● Average intensity of 149mJy.

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I.F. To Back End LPFilter 150MHz

Feed-horn

Software Defined Radio

AMP

Time series “Folding” example.

300

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First Vela detection with “rapulsar” software.

Amplitude [Relative] 0 1 2

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Measured Δt=2.76mSec

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Pulsar Vela processed wit PRESTO tool-chain

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Two simultaneous channel detection of Vela with “rapulsar” software , the difference in time correspond to the time delay according the D.M. Value.

Millisecond Pulsar PSR J0437-4715 processed with PRESTO

Acknowledgment

Conclusions

The author wants to give a special recognition to the work and assistance, to develop the software for the presented work to the following people: ● Peter W. East. ● Steve Olney. ● Wolfgang Herrmann.

With a low cost (U$S 20) SDR receiver of only 2 MHz bandwidth we were able to detect several pulsars, proving the validity and flexibility of the SDR concept. Other commercially available SDR systems with bandwidth of 50 to 100 MHz could allow the detection of fainter pulsars, and give a better estimation of their dispersion characteristics.

References: {1} Poster at 58° AAA Hydrogen Observations using Software Defined Radio and the IAR1 Antenna http://tempo.sourceforge.net/ http://www.cv.nrao.edu/%7Esransom/ransom_thesis_2001.pdf http://www.y1pwe.co.uk/RAProgs/AmateurPulsarDetectionF.doc