Calculation of exponential propagation step responses - accurately for three base frequencies

In the travelling wave approach for calculating transmission line transients an exponential fitting for the propagation step (or impulse) response, has the advantage of allowing to perform the required convolutions recursively. Originally, this involved an inverse Fourier Transform from frequency to time domain, followed by an exponential fitting. This paper describes a procedure for obtaining the step responses directly from the frequency domain, thus avoiding the inverse Fourier Transform, and using only three base frequencies, one of which is 60 Hz. The output is accurate for these frequencies and has little error for others. Consequently, switching operations, which in many cases consist of a transition from steady states involving 60 Hz, can be accurately calculated. The program has been tested for a large variety of actual transmission lines.