A Computer System for Signal Analysis at a Remote Terminal

A computer system which is operated from a remote terminal has been developed at Battelle Memorial Institute, Pacific Northwest Laboratories, to perform Fourier-transform analysis on time data rapidly and accurately. As many as 512 samples can be taken at frequencies up to 20 kHz, or digital data can be read directly into the computer memory. Fourier transforms, cross spectra, and autospectra can be determined for real or complex data. Hardware in the system consists of the computer and its standard peripherals; a general interface, which is a nonstandard peripheral device developed at Battelle-Northwest; and the communication link between the computer and the remotely located user. Software in the system is highly modular and consists of control and mathematical subroutines. Mathematical operations performed are the fast Fourier transform, complex multiplication, and conjugation. Transforms for 512 points can be calculated in five seconds, and a single real signal can be sampled and digitized at 20 kHz. Example calculations show that frequency components with relative amplitude ranges of five decades can be easily recognized. Calculation noise is a factor of a million less than the largest frequency component measured. The remote terminal allows the user with a complex experiment to have full-time direct access to the computer, but the computer room is not cluttered with his special-purpose experimental apparatus.