1. BDT Radio – 1a – CMV 2009/09/01 Basic Detection Techniques Radio Detection Techniques Marco de Vos, ASTRON devos@astron.nl / 0521 595247 Literature: Selected chapters from Krauss, Radio Astronomy, 2 nd edition, 1986, Cygnus- Quasar Books, Ohio, ISBN 1-882484-00-2 Perley et al., Synthesis Imaging in Radio Astronomy, 1994, BookCrafters, ISBN 0-937707-23-6 Selected LOFAR and APERTIF documents Lecture slides

2. BDT Radio – 1a – CMV 2009/09/01 Overview 1a (2011/09/20): Introduction and basic properties Historical overview, detection of 21cm line, major telescopes, SKA Basis properties: coherent detection, sensitivity, resolution 1b (2011/09/22 TBC): Single dish systems Theory: basic properties, sky noise, system noise, Aeff/Tsys, receiver systems, mixing, filtering, A/D conversion Case study: pulsar detection with the Dwingeloo Radio Telescope 2a (2011/09/26): Aperture synthesis arrays Theory: correlation, aperture synthesis, van Cittert-Zernike relation, propagation of instrumental effects Case study: imaging with the WSRT 2b (2011/09/27): Phase array systems Theory: aperture arrays and phased arrays, feed properties, sensitivity, calibration. Case study: the LOFAR system Experiment (2011/09/29 TBC): Phased Array Feed flux measurement Measurements with DIGESTIF (in Dwingeloo)

3. BDT Radio – 1a – CMV 2009/09/01 Different wavelengths, different properties

4. BDT Radio – 1a – CMV 2009/09/01 Coherent detectors Responds to electric field ampl. of incident EM waves Active dipole antenna Dish + feed horn + LNA Requires full receiver chain, up to A/D conversion Radio mm (turnoverpoint @ 300K) IR (downconversion by mixing with laser LOs) Phase is preserved Separation of polarizations Typically narrow band But tunable, and with high spectral resolution For higher frequencies: needs frequency conversion schemes

5. BDT Radio – 1a – CMV 2009/09/01 Horn antennas

6. BDT Radio – 1a – CMV 2009/09/01 Wire antennas, vivaldi

7. BDT Radio – 1a – CMV 2009/09/01 “Unique selling points” of radio astronomy Technical: Radio astronomy works at the diffraction limit ( /D) It usually works at ‘thermal noise’ limit (after ‘selfcalibration’ in interferometry) Imaging on very wide angular resolution scales (degrees to ~100  arcsec) Extremely energy sensitive (due to large collecting area and low photon energy) Very wide frequency range (~5 decades; protected windows ! RFI important) Very high spectral resolution (<< 1 km/s) achievable due to digital techniques Very high time resolution (< 1 nanoseconds) achievable Good dynamic range for spatial, temporal and spectral emission Astrophysical: Most important source of information on cosmic magnetic fields No absorption by dust => unobscured view of Universe Information on very hot (relativistic component, synchrotron radiation) Diagnostics on very cold - atomic and molecular - gas

8. BDT Radio – 1a – CMV 2009/09/01 Early days of radio astronomy 1932 Discovery of cosmic radio waves (Karl Jansky) Galactic centre v=25MHz; dv=26kHz

9. BDT Radio – 1a – CMV 2009/09/01 The first radio astronomer (Grote Reber, USA) Built the first radio telescope "Good" angular resolution Good visibility of the sky Detected Milky Way, Sun, other radio sources (ca. 1939-1947). Published his results in astronomy journals. Multi-frequency observations 160 & 480 MHz

10. BDT Radio – 1a – CMV 2009/09/01 Radio Spectral-lines Predicted by van der Hulst (1944):discrete 1420 MHz (21 cm) emission from neutral Hydrogen (HI). Detected by Ewen & Purcell (1951)

11. 1956

12. ESERO Docentendag - CMV 2008/11/05 1956

13. BDT Radio – 1a – CMV 2009/09/01

14. Connecting Europe …

15. BDT Radio – 1a – CMV 2009/09/01 Giant radio telescopes of the world 1957 76m Jodrell Bank, UK ~1970 64-70m Parkes, Australia ~1970 100m Effelsberg, Germany ~1970 300m Arecibo, Puerto Rico ~2000 100m GreenBank Telescope (GBT), USA

16. BDT Radio – 1a – CMV 2009/09/01 EVLA 27 x 25m dish

17. ASTRON/LOFAR/SKA - CMV 2008/10/06 `

18. 18 Dense Aperture Arrays 2500 Dishes Wide Band Single Pixel Feeds Phased Array Feeds 250 Sparse Aperture Arrays 3-Core Central Region Square Kilometre Array

21. 21 Sparse Aperture Array stations (5 x LOFAR) Artist renditions from Swinburne Astronomy Productions SKA 1 baseline design Single pixel feed Central Region Baseline technologies are mature and demonstrated in the SKA Precursors and Pathfinders 250 x 15-m dishes

23. BDT Radio – 1a – CMV 2009/09/01

24. EM waves Directionality (RA, dec, spatial resolution) Time (timing accuracy, time resolution) Frequency (spectral resolution) Flux (total intensity, polarization properties)

25. BDT Radio – 1a – CMV 2009/09/01

26. BDT Radio – 1b – CMV 2009/09/04 Sensitivity Key question: What’s the weakest source we can observe Key issues: Define brightness of the source Define measurement process Define limiting factors in that process

27. BDT Radio – 1b – CMV 2009/09/04 Brightness function Surface brightness: Power received /area /solid angle /bandwidth Unit: W m -2 Hz -1 rad -2 Received power: Power per unit bandwidth: Power spectrum: w(v) Total power: Integral over visible sky and band Visible sky: limited by aperture Band: limited by receiver

28. BDT Radio – 1b – CMV 2009/09/04 Point sources, extended sources Point source: size < resolution of telescope Extended source: size > resolution of telescope Continuous emission: size > field of view Flux density: Unit: 1 Jansky (Jy) = 10 -26 W m -2 Hz -1

29. BDT Radio – 1b – CMV 2009/09/04 Antenna temperature, system temperature Express noise power received by antenna in terms of temperature of resistor needed to make it generate the same noise power. Spectral power: w = kT/λ 2 A eff Ω a = kT Observed power: W = kT Δv Observed flux density: S = 2kT / A eff Tsys = Tsky + Trec Tsky and Tant: what’s in a name After integration:

30. BDT Radio – 1b – CMV 2009/09/04 System Equivalent Flux Density What’s in Tsys? 3K background and Galactic radio emissionTbg Atmospheric emissionTsky Spill-over from the ground and other directionsTspill Losses in feed and input waveguideTloss Receiver electronicsTrx At times: calibration sourceTcal

31. BDT Radio – 1a – CMV 2009/09/01

34. Sampling

35. BDT Radio – 1a – CMV 2009/09/01 Subband separation Wideband input signal 80 or 100 MHz Separate into 512 small sub-bands 156.25 kHz or 195.3125 kHz bandwidths Out-of-band rejection of a sub-band filter > 80 dB. Polyphase pre-filter, followed by FFT Optional near-perfect reconstruction of time-series

36. BDT Radio – 1b – CMV 2009/09/04 Reception pattern of an antenna Beam solid angle ( A = A/A 0 ) Measure of Field of View Antenna theory: A 0 Ω a = λ 2

37. BDT Radio – 2a – CMV 2009/10/06 Grating lobes

38. vdWaals symposium CMV 2007/12/18

40. BDT Radio – 1a – CMV 2009/09/01 Timing Rubidium (Rb) laser reduces variance in the GPS-PPS to < 4 ns rms over 105 sec. The output of the Rb reference is distributed to the Time Distribution Sub-rack (TDS). Reference frequency is converted to the sampling frequency: using 10 MHz reference and Phase Locked Loops (PLL) in combination with a Voltage Controlled Crystal Oscillator (VCXO), the jitter of the output clock signals are minimized. Within a sub-rack all clock distribution is done differentially to reduce noise picked up by the clock traces and to reduce Electro Magnetic Interference (EMI) by the clock.