Using your own PC to analyse the recorded signals - which are mostly just random noise
Alien transmit frequency GHz
Alien transmit antenna diameter m
Alien transmit antenna gain dBi
Alien transmit power W
Alien transmit EIRP dBW
Receive antenna diameter m
Receive system noise temperature(antenna+LNA) K
Receive antenna gain dBi
Receive antenna G/T dB/K
Bandwidth Hz
Required overall link carrier to noise ratio C/N dB
Path (spreading) loss dB
Range km
Range AU (1AU=Earth to Sun distance)
Range light seconds
Range light minutes
Range light years


Input your idea of what the alien transmitter might use in terms of:

 Frequency (in GHz) and Transmit Antenna Diameter (in meters).

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).

Choose something more than 0.1 Hz to avoid dispersion and phase noise and to give a chance for some useful information to get through. 

Input also your dish diameter (in meters) and system noise temperature (in deg Kelvin). 

Use the nominal 50K if you don't understand this. 

Input what Carrier to Noise ratio you think you need to detect something.

If you have time to do long averaging of a CW (continuous wave i.e. un-modulated) source then a C/N = 0 dB might be adequate.

You would detect a 3 dB hump in the noise floor ((C+N)/N) once the short term noise was averaged out.

If you need quick detection with a moving antenna or moving source then a detection threshold C/N = 5 dB or higher might be better.