Receiver Systems Suzy Jackson – based on previous talks by Alex Dunning & Graeme Carrad

The Basic Structure of a typical Radio Telescope CSIRO. Receiver Systems for Radio Astronomy Antenna Receiver ConversionDigitiser Signal Processing / Correlator

Ours look like this... CSIRO. Receiver Systems for Radio Astronomy ATCA 3/7/12mm Parkes 10/50cm MRO PAF

The Receiver CSIRO. Receiver Systems for Radio Astronomy On the outside... Vacuum Dewar Feed Horns

The Receiver CSIRO. Receiver Systems for Radio Astronomy On the inside... Amplifiers Ortho-Mode Transducers

CSIRO. Wide Band Receiver Upgrade of the CASS Compact Array system temperature Integration Time minimum detectable flux Effective Collecting Area Observing Bandwidth

The Australia Telescope Receivers CSIRO. Receiver Systems for Radio Astronomy 10cm-25cm 12mm-18.7mm 6mm-10mm O 2 absorption 2.8mm-3.5mm 4.6cm-6.7cm 3.2cm-3.7cm 2.5cm-7cm Current upgrade L/S C/X K Q W

Parkes Receiver Bands CSIRO. Receiver Systems for Radio Astronomy

Receiving the signal – Feed horns CSIRO. Receiver Systems for Radio Astronomy Feed Signal Waveguide output Captures the focused microwaves into a waveguide output

Feed Horns CSIRO. Receiver Systems for Radio Astronomy Designed to match the focal ratio of the antenna Matches the waveguide impedance to free-air impedance Design compromises: Size & weight Spillover/efficiency Bandwidth Loss

Coupling noise into the System CSIRO. Receiver Systems for Radio Astronomy Feed Signal Noise source Coupler 7mm waveguide coupler Noise coupled in through small holes Noise coupled in through vane 21cm waveguide coupler 12mm noise source

Separating Polarisations – Ortho-mode Transducers (OMTs) CSIRO. Receiver Systems for Radio Astronomy Polariser Feed Signal Noise source Coupler Pol B Pol A Separates incoming signal into two linear or circular polarisations Linear OMTs exhibit higher polarisation purity over broad frequency bands (usually) 12mm Ortho-mode transducer 4cm Ortho-mode transducer 3mm Ortho-mode transducer

Low Noise Amplifiers (LNA) CSIRO. Receiver Systems for Radio Astronomy Polariser Feed Signal Noise source Coupler LNA To conversion System Pol B Pol A High Electron Mobility Transistor (HEMT)

Feed Signal LNA Second Stage Amplifier Third Stage Amplifier T1T1 T2T2 T3T3 Why is the first Low Noise Amplifier so important?

The Conversion System CSIRO. Receiver Systems for Radio Astronomy Contains: more amplification band defining filters frequency conversion level adjustment signal detection band shaping Frequency Conversion Signal Filter To Digitiser Amplifier Level Adjustment

Filters CSIRO. Receiver Systems for Radio Astronomy High Pass Filter Low Pass Filter Band Pass Filter 21cm band filter

Mixing it down – Frequency Conversion CSIRO. Receiver Systems for Radio Astronomy Signal 1 Signal 2 Signal 1 × Signal 2 Mixer (Multiplier) Frequency Power Frequency Power cos(ω 1 t)cos(ω 2 t)=½[cos((ω 1 +ω 2 )t)+ cos((ω 1 -ω 2 )t)] ΔfΔfΔfΔf

Mixing it down – Frequency Conversion CSIRO. Receiver Systems for Radio Astronomy Signal 1 Signal 2 Mixer (Multiplier) Frequency Power Frequency Power cos(ω 1 t)cos(ω 2 t)=½[cos((ω 1 +ω 2 )t)+ cos((ω 1 -ω 2 )t)] ΔfΔfΔfΔf Low pass filter

Mixing it down – Frequency Conversion CSIRO. Receiver Systems for Radio Astronomy Signal 1 Mixer (Multiplier) Frequency Power Frequency Power ΔfΔfΔfΔf Local Oscillator f lo cos(ω 1 t)cos(ω LO t) → ½cos[(ω 1 -ω LO )t] Upper Side Band (USB)

Mixing it down – Frequency Conversion CSIRO. Receiver Systems for Radio Astronomy Signal 1 Mixer (Multiplier) Frequency Power Frequency Power ΔfΔf ΔfΔf Local Oscillator f lo cos(ω 1 t)cos(ω LO t) → ½cos[(ω LO -ω 1 )t] Lower Side Band (LSB)

Mixing it down – Frequency Conversion CSIRO. Receiver Systems for Radio Astronomy Signal 1 Mixer (Multiplier) Frequency Power Frequency Power ΔfΔfΔfΔf Local Oscillator f lo Band pass filter

Single Sideband Mixers CSIRO. Receiver Systems for Radio Astronomy RF Signal 2√2cos(ω 1 t) 2cos(ω 1 t) 2sin(ω 1 t) sin[(ω 1 - ω LO )t] (USB) -sin[(ω LO - ω 1 )t] (LSB) cos[(ω 1 - ω LO )t] (USB) cos[(ω LO - ω 1 )t] (LSB) -cos[(ω 1 - ω LO )t] (USB) cos[(ω LO - ω 1 )t] (LSB) 0(USB) √2cos[(ω 1 - ω LO )t] (LSB)

Single Sideband Mixers CSIRO. Receiver Systems for Radio Astronomy RF Signal 2√2cos(ω 1 t) √2cos[(ω LO - ω 1 )t] (USB) 0(LSB) Signal Local Oscillator Lower sideband Upper sideband

I/Q Mixers CSIRO. Receiver Systems for Radio Astronomy RF Signal 2√2cos(ω 1 t) 2cos(ω 1 t) sin[(ω 1 + ω LO )t] -sin[(ω 1 -ω LO )t] cos[(ω 1 - ω LO )t] +cos[(ω 1 +ω LO )t] -sin[(ω 1 - ω LO )t] cos[(ω 1 - ω LO )t] I/Q Baseband Signal

Or Graphically CSIRO. Receiver Systems for Radio Astronomy RF Signal Frequency Power Frequency ΔfΔf f lo I/Q Baseband Signal Power ΔfΔf

Attenuators – The Volume Knob CSIRO. Receiver Systems for Radio Astronomy Allow the signal level to be varied May be several in the system Usually set automatically Just like some other systems if you turn the signal down too far all you get is noise and if you turn it up to far you get distortion!

CSIRO. Receiver Systems for Radio Astronomy Of course real systems are a little more complicated. They often contain multiple conversions and many amplification and filter stages.... But that’s the gist of it.

What is the rest of the stuff? CSIRO. Receiver Systems for Radio Astronomy What’s this?

Electronics CSIRO. Receiver Systems for Radio Astronomy Supplies and monitors all amplifier voltages and currents Monitors system temperatures and pressures

Cryogenics CSIRO. Receiver Systems for Radio Astronomy 15K section 80K section Helium Lines Helium Compressor Helium Refrigerator Refrigerator in the Parkes 12mm receiver Cold finger

CSIRO. Receiver Systems for Radio Astronomy Copper Radiation Shield 80K Helium Refrigerator cold finger Vacuum Dewar Thermal Isolation waveguide 15K section Low Noise Amplifiers Gap

CSIRO. Receiver Systems for Radio Astronomy ….but why do we need to cool our receivers at all?

How weak is the signal? CSIRO. Receiver Systems for Radio Astronomy Your hand → 1.38× W Hz -1 K -1 × 300K × 1 × 10 9 Hz = 4 × W 10Jy radio source → 10 × W m -2 Hz -1 × 1900m 2 × 1 × 10 9 Hz = 2× W Mobile Phone → ≈ 1W Mobile Phone on the moon→ ≈ 1W ÷ 4π (3.8×10 8 m) 2 ÷ 5×10 6 Hz ≈ 10Jy Effective area of Parkes telescope dish Bandwidth of Digital Filter Bank 3 Boltzmann's constant Lunar Distance 3G transmit bandwidth

Like your hand all the components in the receiver system contribute a thermal noise signal which masks the astronomical signal we are trying to observe. By cooling the receiver we reduce these thermal sources of noise and improve the sensitivity of the receiver by 7-10 times. CSIRO. Receiver Systems for Radio Astronomy

Reduce noise by cooling CSIRO. Receiver Systems for Radio Astronomy Electronic device generates a signal Cold stuff (liquid nitrogen) – good for making ice cream.

Contact Us Phone: or Web: Thank you CSIRO Astronomy and Space Science Suzy Jackson RF Engineer Phone: Web: