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A radio polarimeter spectrometer

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Hall, PJ (1984) A radio polarimeter spectrometer. PhD thesis, University of Tasmania.

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Abstract

For several years it has been apparent that a requirement in
radioastronomy is a device capable of providing high time resolution
polarization spectra of a wide bandwidth. This thesis describes
such an instrument. The new polarimeter spectrometer is based on
two surface acoustic wave (SAW) spectrum analysers operating in a
coherent (phase preserving) mode. The method of spectrum analysis
is a high sensitivity one, the analysers being more akin to filterbank
types than to swept-frequency instruments.
A wideband analog multiplier has been developed, permitting
the spectrum analyser outputs to be correlated directly to yield
cross-spectral or polarization data. As well, the usual problem
with SAW analysers - the high output data rate - has been overcome
with the development of a fast digital spectrum integrator. This
device allows the SAW intermediate-frequency processor to be
interfaced to a general purpose computer, resulting in a real-time
signal processing system with great versatility.
The prototype SAW processor produces polarization spectra
over a bandwidth of about 30 MHz with frequency and time resolutions
of 650 kHz and 2.4 uS. When interfaced to a typical computer,
Stokes polarization spectra with a time resolution of about 150 uS
are available. After allowing for non-continuous operation of the
prototype spectrum analysers, the radiometer efficiency of the
complete processing system exceeds 70%. Most techniques used in the
development of the first polarimeter spectrometer are applicable to
larger scale instruments.
Although primarily the report on a project in applied signal
processing, this thesis contains three other main sections. Firstly,
an extensive and up-to-date review of SAW spectrum analysis and
associated techniques is included. Secondly, the results of a
series of numerical simulations are given. The simulations relate
to the performance of post-detection digital integrators when quantizing
envelope-detected, inverse bandwidth noise.
In the third major section of the thesis, data from initial
scientific observations conducted using the new instrumentation are presented. The SAW and digital processors, together with other
items of hardware constructed in the course of the research project,
were used in conjunction with the 14 m steerable radio telescope
at the Llanherne (Hobart) observatory. As well as confirming
laboratory radiometer efficiency measurements, the first astronomical
data from the new system have been used to demonstrate changes in the
rotation and dispersion measures of the Vela pulsar, PSR 0833-45.
The rotation measure change is in general agreement with a
trend deduced by earlier workers. The change in dispersion
measure is only the second confirmed for any pulsar, the first changes
being reported more than 10 years ago for the Crab nebula pulsar.
The present variation is over 100 times the order of the Crab pulsar
changes and amounts to more than 1% of the Vela pulsar dispersion
measure reported by investigators in 1970. The new data support the
hypothesis of relative motion between PSR 0833-45 and a magnetized
filament in the Vela supernova remnant.

Item Type: Thesis (PhD)
Keywords: Radio astronomy, Spectrum analysis, Polariscope, Spectrometer
Copyright Holders: The Author
Copyright Information:

Copyright 1984 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 1985.

Date Deposited: 08 Dec 2014 23:58
Last Modified: 27 Mar 2017 23:46
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