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