This useful Windows program calculates the theoretical lower limit of the signal strength that can be detected by a radiotelescope. Several parameters are required, yielding graphs for various bandwidths and integration times.
This program is Free! courtesy of Dave Halley, the author. Please note: all technical support for this program is provided by its author only. After running the program, see the program About box for contact information. There is no installation program, just download the program to a handy place (such as your desktop) and run it.