BDT Radio – 1b – CMV 2009/09/04 Basic Detection Techniques 1b (2011/09/22): Single dish systems Theory: basic properties, sky noise, system noise, Aeff/Tsys, receiver systems, mixing, filtering, A/D conversion Case study: LOFAR Low Band Antenna

BDT Radio – 1b – CMV 2009/09/04 Basic Detection Techniques Visit to Dwingeloo for APERTIF measurements 2011/09/29 13:00-15:00 NS to Beilen: 13:31-13:58 NS fm Beilen: 16:59-17:28 Transport Beilen – Dwl vv will be arranged by ASTRON Call (Diana van Dijk) in case of problems Host is Laurens Bakker APERTIF System Engineer)

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

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

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) = W m -2 Hz -1

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

BDT Radio – 1b – CMV 2009/09/04 Black-body radiation General: Planck’s radiation law Radio frequencies (hv << kT): Rayleigh-Jeans law (or rather: R-J approximation)

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:

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

BDT Radio – 1b – CMV 2009/09/04 System Equivalent Flux Density K is only related to Tant, not to 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

BDT Radio – 1b – CMV 2009/09/04 Example: EVLA (slides Rick Perley, jul 2010)

BDT Radio – 1b – CMV 2009/09/04 Example: EVLA (slides Rick Perley, jul 2010)

BDT Radio – 1b – CMV 2009/09/04 Example: EVLA (slides Rick Perley, jul 2010)

BDT Radio – 1b – CMV 2009/09/04 Example: MFFE

BDT Radio – 1b – CMV 2009/09/04 Example: MFFE

BDT Radio – 1b – CMV 2009/09/04

Receiver chain at WSRT

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

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

BDT Radio – 1b – CMV 2009/09/04 Wire antennas, vivaldi

BDT Radio – 1b – CMV 2009/09/04

ESERO Docentendag - CMV 2008/11/05 High time resolution data (LOFAR // Nancay Decametric Array) Blow-up: 0.2 seconds showing complex structure

BDT Radio – 1b – CMV 2009/09/04