[Al Skierkiewicz]

Techno et al,
There are all sorts of ways to detect noise and cancel it out or pull data from it. Modern DSP (digital signal processing) can do marvelous things. For just about one hundred dollars there are DSP add ons for ham radios that reduce noise 20-30 dB. In these applications, the DSP is not noise canceling as much as signal enhancing. Noise cancelling for me means multiple loud sounds only one of which you want to hear. You filter out the noise, invert it and add it back in out of phase to "cancel" the unwanted sounds.
Now there are other methods for pulling signals out of a mixed environment. NASA uses these techniques in order to communicate with distant objects like the Mars explorers. It is easy when you have an unlimited power supply or huge antenna array, to crank out enough power to overcome the losses of distance in radio communications. But when you are limited by power and size, you must come up with other ways to insure "no data radio" will hamper you project. By using these techniques, NASA is able to demodulate signals that are below the noise floor. For standard voice communications, you need about 35-40 dB signal to noise for the parties to be understood. If both of you know that a limited vocabulary will be used or are willing to repeat messages until understood, then less than 30 dB S/N is tolerable. For data and morse code (with no DSP) a few dB S/N is OK. When you get to the point where the signal is 10-20 dB below noise, you better have a powerful DSP set and high gain antennas to get the data through.