Radio Astronomy and SETIRadio Astronomy and SETIJenny Bailey G0VQH

Bernie Wright G4HJW

IntroductionHistory of Radio AstronomySETIPractical Radio AstronomyPractical SETIQuestions

Is there anyone out there ?Is there anyone out there ?

The Drake Equation :

LfffnfRN cilep Where

N = The number of civilisations trying to contact usR = The average rate of Star Formationfp = The fraction of stars that are suitable for planet formationne = Number of Earth-like planetsfl = Fraction of Earth-like planets where life develops fi = Fraction of Earth-like planets where life has intelligencefc = Fraction of intelligent species who want to communicate L = Lifetime of a civilisation

Where Should we lookWhere Should we look

Frequency Radio - The ‘Water Hole’

Optical

Gravity Waves

The next big discovery

PolarisationCircular, linear, modulated ?

Direction Targeted search

All-Sky survey

Radio LeakageIntentional messages

RF leakage

ModulationNarrow band signals - preferably pure CW.

The ‘Water Hole’The ‘Water Hole’

SETI ProjectsSETI Projects

Arecibo/Jodrell BankProject ArgusSETI@HomeOptical SETI

How far can we hear ?How far can we hear ?

Distant civilisation wants to signal us.Tx : Assume 1GW into a 300m dish at 1420MHz .

Rx : Assume Project Argus station as receiver - 4m dish. GaAsFET LNA 10Hz channels.

The SETI League, Inc. Link AnalysisUser specifies variables shown in Bold

Transmitter:Frequency = 1420 MHz; 21.1 cm

Transmit Power = 1.0E+09 W = 90.0 dBW = 120.0 dBmEff. antenna diam. = 300 meters = 984 ft

Illum. Efficiency = 85 %Computed Antenna Gain = 1.7E+07 Ap = 72.3 dBi

Antenna Half Power Beamwidth = 7.2E-04 radian = 4.2E-02 degreesEffective Isotropic Radiated Pwr = 1.7E+16 W = 192.3 dBm

Path:Range = 30 parsecs = 97.8 LY = 9.3E+17 m

Free Space Isotropic Path Loss = 394.8 dBIncident Isotropic Power = EIRP - path loss = -202.5 dBm

Receiver:Eff. antenna diam. = 5 meters = 16.4041667 ft

Illum. Efficiency = 50 %Computed Antenna Gain = 2.8E+03 Ap = 34.4 dBi

Antenna Half Power Beamwidth = 4.3E-02 radian = 2.5E+00 degrees

What signal should we look for ?What signal should we look for ?

A signal with Doppler shiftA signal with Doppler shift would indicate non-terrestrial. CW

signal to get attentionA CW beacon would stand out from Galactic noise

Can be seen with low bandwidth receiver

A modulated signal This will spread the signal over a wide bandwidth and make the

signal hard to detect

Should we TransmitShould we Transmit

A signal was sent from the Arecibo Telescope to celebrate its commissioning.

This was controversial because :– The message was very USA-centric. It was argued that

any message should be agreed by all nations.– We should not attract attention to our planet, we might

invite BAD aliens.

How do we search ?How do we search ?

We need to look at as much Bandwidth as possible

The receiver must have a narrow Bandwidth to enhance the sensitivity

Use an ex-PMR FM radio modified to product detect - creating a 25KHz wide SSB receiver

Synthesise narrow receive filters using PC running FFT software to chop the receiver bandwidth into many 10Hz channels.

Average each 10Hz channel over a few seconds to improve receiver sensitivity

Signal VerificationSignal Verification

A signal from a distant star will have the following characteristics :

The signal will come and go with the response of the receiving aerial

The signal will have Doppler shift corresponding to the Earth’s spin and rotation around the sun.