Developing a digital signal Developing a digital signal Work on digital transmission began back in the 1920s, when Bell System researcher Harry Nyquist determined that it was possible to encode an analog signal in digital form if the analog signal was sampled at twice its frequency. Each sample could then be encoded and transmitted, and there would be enough information in the encoded signal for the original voice signal to be reconstructed into a understandable analog signal at the receiving end. The electronics fast enough to sample, encode, and transmit signals didn't exist in Nyquist's time, and it wasn't possible to develop a practical commercial digital system until three Bell Labs researchers, Walter Brattain, John Bardeen and William Shockley, invented the transistor in 1947. This figure shows two voltage levels.
Some transmission systems have three or more levels, which aids in error detection.
A digital signal has fixed amplitude and frequency. Use of this site indicates you accept the Terms of Use and the Privacy Statement . Please contact Bell Labs with any technical comments or questions about this site.