correlators_mar2

correlators_mar2 - Cross Correlators Greg Taylor University...

Info iconThis preview shows pages 1–13. Sign up to view the full content.

View Full Document Right Arrow Icon
Astronomy 423 at UNM Radio Astronomy Cross Correlators Greg Taylor University of New Mexico Spring 2011
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
G. Taylor, Astr 423 at UNM 2 Outline The correlation function What is a correlator? Simple correlators Sampling and quantization Spectral line correlators The EVLA correlator in detail This lecture is complementary to Chapter 4 of ASP 180 and is based on a lecture by Walter Brisken
Background image of page 2
G. Taylor, Astr 423 at UNM 3 The [old] VLBA Correlator
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
G. Taylor, Astr 423 at UNM 4 The Correlation Function
Background image of page 4
G. Taylor, Astr 423 at UNM 5 The Correlation Function If it is an auto-correlation (AC). Otherwise it is a cross-correlation (CC). Useful for Determining timescales (CC and AC) Motion detection (2-D CC) Optical character recognition (2-D CC) Pulsar timing / template matching (CC)
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
G. Taylor, Astr 423 at UNM 6 What is a Correlator? Visibilities are in general a function of Frequency Antenna pair Time They are used for Imaging Spectroscopy / polarimetry Astrometry A correlator is a hardware or software device that combines sampled voltage time series from one or more antennas to produce sets of complex visibilities, .
Background image of page 6
G. Taylor, Astr 423 at UNM 7 A Real (valued) Cross Correlator
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
G. Taylor, Astr 423 at UNM 8 Visibilities What astronomers really want is the complex visibility where the real part of is the voltage measured by antenna . So what is the imaginary part of ? It is the same as the real part but with each frequency component phase lagged by 90 degrees.
Background image of page 8
G. Taylor, Astr 423 at UNM 9 The Complex Correlator
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
G. Taylor, Astr 423 at UNM 10 Time Series, Sampling, and Quantization are real-valued time series sampled at “uniform” intervals, . The sampling theorem allows this to accurately reconstruct a bandwidth of . Sampling involves quantization of the signal Quantization noise Strong signals become non-linear Sampling theorem violated!
Background image of page 10
G. Taylor, Astr 423 at UNM 11 Quantization Noise
Background image of page 11

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
G. Taylor, Astr 423 at UNM 12 Automatic Gain Control (AGC) Normally prior to sampling the amplitude level of each time series is adjusted so that quantization noise is minimized. This occurs on timescales very long compared to a
Background image of page 12
Image of page 13
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 12/13/2011 for the course ASTRO 423 taught by Professor Gregtaylor during the Fall '11 term at New Mexico.

Page1 / 36

correlators_mar2 - Cross Correlators Greg Taylor University...

This preview shows document pages 1 - 13. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online