basic detection techniques
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BDT Radio – 1b – CMV 2009/09/04
Basic Detection Techniques
1b (2011/09/22): Single dish systemsTheory: 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 measurements2011/09/29 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 0521 595119 (Diana van Dijk) in case of problems
Host is Laurens BakkerAPERTIF 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) = 10-26 W m-2 Hz-1
BDT Radio – 1b – CMV 2009/09/04
Reception pattern of an antenna
Beam solid angle (A = A/A0)Measure of Field of View
Antenna theory: A0 Ωa = λ2
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)
de
hdP
kTh 1/
TkP
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/λ2 Aeff Ωa = kTObserved power: W = kT Δv
Observed flux density: S = 2kT / Aeff
Tsys = Tsky + TrecTsky and Tant: what’s in a name
After integration: B
TTT
recsky
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 KK is antenna’s gain or “sensitivity”
unit: degree Jy1
aTkGP
SAGP a21
k
A
S
TK aa
2
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 emission Tbg
Atmospheric emission Tsky
Spill-over from the ground and other directions Tspill
Losses in feed and input waveguide Tloss
Receiver electronics Trx
At times: calibration source Tcal
][2
JyA
Tk
K
TSEFD
a
syssys
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
BDT Radio – 1b – CMV 2009/09/04
Receiver chain at WSRT
Recv.Recv.
Equal.Equal.
IVCIVC
ADCADC
Recv.Recv.
Equal.Equal.
IVCIVC
ADCADC
west east
TADU
TADU
LOLO LOLOVLBIVLBI PuMaPuMa
CorrelatorCorrelator
Ref. Ref.
BDT Radio – 1b – CMV 2009/09/04
Horn antennas
BDT Radio – 1b – CMV 2009/09/04
Inside the MFFE
UHFlow UHFhigh 92 49 13 18/21 6 3.6
swsw
LO1 lowSynth.
LO1 lowSynth.
swsw
1200-2200 MHz
1 GHzIF1 IF1
LO1 highSynth.
LO1 highSynth.
swsw
2200-9600 MHz
1 GHz
1 GHz
LO2Synth.
LO2Synth.
900 MHz
2x IF out100 ± 80 MHz
Cryogenic
BDT Radio – 1b – CMV 2009/09/04
Wire antennas, vivaldi
BDT Radio – 1b – CMV 2009/09/04
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
to receiver
1..16on/off delaystep
on/off delaystep
BDT Radio – 1b – CMV 2009/09/04
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