Prelimiting Bandpass Filtering on Fading Radio Circuits

On channels subject to multipath propagation, the prelimiting bandpass filtering technique is shown to be a factor of great importance in determining the over-all performance. Minimum-loss, fiat-topped filters create serious transient effects which add greatly to the error rate in data transmission. Because of adjacent channel requirements, an over-all Gaussian response is not applicable. A practical solution is considered to be a rounded-top filter composed of a series of synchronous-tuned single circuits in cascade. Tests and observations are described, leading to the application of these filters on an independent side band (ISB) telegraph circuit. A threefold improvement in the error rate of 45-baud printer operation resulted, as well as reduction of distortion for timedivision multiplex operation.