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SETI Range Calculator : Example using GBT parameters 2023
The purpose of this page is to allow you to determine the range at which a possible alien radio transmission can be detected, using your choice of assumptions about frequency, antenna dish size, receiver bandwidth etc.
Radio communications from planets around distant stars.
Complete all the light grey boxes below (by modifying the default values shown) and then click the calculate button to obtain results in the green boxes.
Press calculate and see what is the resulting maximum range, if a signal is to be detected.
Repeat the range calculation several times, experimenting with different powers, bandwidths, antenna sizes etc.
Have fun and good luck.
Here are some GBT parameters corresponding recent SETI searches using the Greenbank Antenna.
Frequency: 1.5 GHz
Diameter receive dish: 100m
Efficiency: 0.72
Receive system noise temperature: 20K.
The alien (ET) transmitter
might be envisioned with a CW carrier to be detected in a 3 Hz bandwidth.
Diameter: 100m.
Transmit power: 650 MW (+ 28.1 dBW)
Try smaller diameters, 1m, 10m etc.
Try powers like 650W, 65kW and 6.5 MW.
Input your idea of what the alien transmitter might use in terms of: Frequency (in GHz) and Transmit Antenna Diameter (in metres). Be cautious about combinations that give extreme gain (more than 80 dBi) as it may (or may not) be difficult for aliens to make such dishes with sufficient surface accuracy. Input an alien Transmitter Power (in watts).
Your receive system will have a bandwidth (in Hz). THe SETI researchers have choosen something like 3 Hz to aloow for dispersion and phase noise and maybe to give a chance for some useful information getting through. Input also your dish diameter (in metres) and system noise temperature (in deg Kelvin). Use the nominal 20K if you don't understand this. Higher values than 20K, such as in the range 50K - 100K, are normal for uncooled LNAs and antennas with less good sidelobes.
Input what Signal to Noise ratio you think you need to detect something. If you have time (e.g. several seconds) to do averaging of a CW (continuous wave i.e. un-modulated) source then a S/N around 0 dB might be adequate. You would detect a 3 dB hump in the noise floor ((S+N)/N=3 dB for a S/N=0dB) once the short term signal and noise variations were averaged out. If you need quick detection with a moving antenna or moving source then a detection threshold S/N = 5 dB or higher might be better. If you are really patient, say 100 seconds or more, a signal that is well below the noise floor is still detectable if you look carefully, as with the default S/N= -12 dB above. This will cause a small hump to build up with long term averaging. Even lower S/Ns are detectable with patience and if you know where to look!
I note that the Search for Technosignatures with the Green Bank Telescope use a S/N threshold of 10. Their S/N calculation is affected by bandwidth and integration time. The meaning of their S/N is explained in the pdf document A Search for Technosignatures Around 11,680 Stars with the Green Bank Telescope at 1.15 - 1.73 GHz. I don't understand it at all but their figure of 10 seems to to have the same meaning as my -12 dB !
I've just found another good document here: The Breakthrough Listen Search for Intelligent Life: 1.1 - 1.9 GHz Observations of 692 Nearby Stars
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I am interested to know if this page gives correct results. If you agree or disagree please send details to me by e-mail Eric Johnston Copyright (c) 2023 Eric Johnston, All Rights Reserved. If you have a web site please add a link direct to this page rather than copying it. Page started: 16 Sept 2023, last amended 23 March 2024. |