A cross‐correlation receiver for radio astronomy employing quadrature channel generation by computed Hilbert transform

Lo, Wei-Chi; Dewdney, P. E.; Landecker, T. L.; Routledge, D.; Vaneldik, J. F.

doi:10.1029/rs019i005p01413

Cited by 9 publications

(6 citation statements)

References 7 publications

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“…Since the in-phase and quadrature visibility outputs are required at only a single value of delay, the convolution degenerates to a simple dot product, requiring multiplication of each value of the correlation function by a matching coefficient from the kernel function. This is a simple and quick operation in the microprocessor (see Lo et al 1984 for details). A small error (of the order of 5%) arises in the derivation of the quadrature visibility because of truncation of the kernel.…”

Section: -Mhz Continuum Correlatormentioning

confidence: 99%

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The synthesis telescope at the Dominion Radio Astrophysical Observatory

Landecker

Dewdney

Burgess

et al. 2000

Astron. Astrophys. Suppl. Ser.

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114

103

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Abstract.We describe an aperture synthesis radio telescope optimized for studies of the Galactic interstellar medium (ISM), providing the ability to image extended structures with high angular resolution over wide fields. The telescope produces images of atomic hydrogen emission using the 21-cm H i spectral line, and, simultaneously, continuum emission in two bands centred at 1420 MHz and 408 MHz, including linearly polarized emission at 1420 MHz, with synthesized beams of 1 and 3.4 at the respective frequencies. A full synthesis can achieve a continuum sensitivity (rms) of 0.28 mJy/beam at 1420 MHz and 3.8 mJy/beam at 408 MHz, and the 256-channel H i spectrometer has an rms sensitivity of 3.5B −0.5 sin δ K per channel, for total spectrometer bandwidth B MHz and declination δ. The tuning range of the telescope permits studies of Galactic and nearby extragalactic objects. The array uses 9 m antennas, which provide very wide fields of view of 3.1• and 9.6 • (at the 10% level), at the two frequencies, and also allow data to be gathered on short baselines, yielding extremely good sensitivity to extended structure. Single-antenna data are also routinely incorporated into images to ensure complete coverage of emission on all angular scales down to the resolution limit. In this paper we describe the telescope and its receiver and correlator systems in detail, together with calibration and observing strategies that make this instrument an efficient survey machine.

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Section: -Mhz Continuum Correlatormentioning

confidence: 99%

“…The C74 correlator was designed to carry out interferometer signal-processing operations in simple software procedures to the maximum extent feasible (Lo et al 1984). Figure 5 is a diagram of the system, showing the distribution of signal-processing functions between hardware and software.…”

Section: -Mhz Continuum Correlatormentioning

confidence: 99%

The synthesis telescope at the Dominion Radio Astrophysical Observatory

Landecker

Dewdney

Burgess

et al. 2000

Astron. Astrophys. Suppl. Ser.

Self Cite

114

103

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“…8.8. The correlation as a function of measured using a correlator with a quadrature phase shift in one input is the Hilbert transform of the same quantity measured without the quadrature phase shift (Lo et al 1984). …”

Section: Simple and Complex Correlatorsmentioning

confidence: 99%

Response of the Receiving System

Thompson

Moran

Swenson

2017

Astronomy and Astrophysics Library

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This chapter is concerned with the response of the receiving system that accepts the signals from the antennas, amplifies and filters them, and measures the crosscorrelations for the various antenna pairs. We show how the basic parameters of the system affect the output. Some of the effects were introduced in earlier chapters and are here presented in a more detailed development that leads to consideration of system design in Chaps. 7 and 8. At some point in the processing chain between the antenna and the correlator output, the form of the signals is changed from an analog voltage to a digital format, and the resulting data are thereafter processed by computer-type hardware. This does not affect the mathematical analysis of the processing and is not considered in this chapter. However, the digitization introduces a component of quantization noise, which is analyzed in Chap. 8. Frequency Conversion, Fringe Rotation, and Complex Correlators Frequency ConversionWith the exception of some systems operating below 100 MHz, in most radio astronomy instruments, the frequencies of the signals received at the antennas are changed by mixing with a local oscillator (LO) signal. This feature, referred to as frequency conversion or (heterodyne frequency conversion), enables the major part of the signal processing to be performed at intermediate frequencies that are most appropriate for amplification, transmission, filtering, delaying, recording, and similar processes. For observations at frequencies up to roughly 50 GHz, the best sensitivity is generally obtained by using a low-noise amplifying stage before the frequency conversion.

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“…These effects are most serious in broad-bandwidth systems, in which the high data rate permits only simple processing. Lo et al (1984) have described a system in which the real part of the correlation is measured as a function of time offset, as described below for the spectral correlator, and the imaginary part is then computed by Hilbert transformation.…”

Section: Quadrature Phase Shift Of a Digital Signalmentioning

confidence: 99%