1. BDT Radio – 1b – CMV 2009/09/04 Basic Detection Techniques 1b (2009/09/04): Single pixel feeds Theory: Brightness function Beam properties Sensitivity, sky noise, system noise, Aeff/Tsys Receiver systems, mixing, filtering Case study: the LOFAR Low Band Antenna Reference frequency Bandwidth Beampattern

2. BDT Radio – 1b – CMV 2009/09/04 EM waves Directionality (RA, dec, spatial resolution) Time (timing accuracy, time resolution) Frequency (spectral resolution) Flux (total intensity, polarization properties)

3. BDT Radio – 1b – CMV 2009/09/04 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 Phase is preserved Separation of polarizations Typically narrow band But tunable, and with high spectral resolution For higher frequencies: needs frequency conversion schemes

4. 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

5. 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

6. 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

7. 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

8. BDT Radio – 1b – CMV 2009/09/04 Black-body radiation General: Planck’s radiation law Radio frequencies (hf << kT): Rayleigh-Jeans law (or rather: approximation) B = 2kT/λ 2

9. 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:

10. BDT Radio – 1b – CMV 2009/09/04 Sensitivity Source power from Ta: Source power from flux: Antenna area A, efficiency  a Rx accepts 1/2 radiation from unpolarized source Define scaling factor K K is antenna’s gain or “sensitivity” unit: degree Jy  1

11. BDT Radio – 1b – CMV 2009/09/04 System Equivalent Flux Density Covers Tant, not Tsys Define SEFD: 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

12. BDT Radio – 1b – CMV 2009/09/04 Example: VLA and MFFE

13. BDT Radio – 1b – CMV 2009/09/04 Receiver chain at WSRT

14. BDT Radio – 1b – CMV 2009/09/04 Horn antennas

15. BDT Radio – 1b – CMV 2009/09/04 Inside the MFFE

16. BDT Radio – 1b – CMV 2009/09/04

17. Wire antennas, vivaldi

18. BDT Radio – 1b – CMV 2009/09/04

21. Sampling

22. BDT Radio – 1b – CMV 2009/09/04 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