A PDM-to-digital encoder and translator

Development of the PDM-to-digital encoder and associated translator resulted from a requirement to preserve the accuracy of pulse-duration modulation (PDM) telemetered data. Deterioration of accuracy in the data reduction or “playback” of such data is avoided by digitizing the data directly at the output of the receiver and recording the digitized data in serial form on a standard PDM channel of a magnetic tape recorder such as an Ampex model 309 using Ampex model 303 pulse amplifiers. The pulse duration is measured at the half-amplitude level of the PDM pulses for the digitizing process to minimize the effects of variations in amplitude and rise and fall times. Once the PDM data are digitized, no error is introduced by the PDM circuitry or wow-and-flutter characteristics of the tape recorder. Range timing is recorded on a standard channel adjacent to the PDM channel. A translator is required at the data-reduction facility to convert the digital data recorded on a conventional PDM tape recorder channel into a format suitable for computer or buffer equipment use. The translator, with associated time code reader to read the tape recorded range timing, supplies a time tag with a time resolution of 1 millisecond for each digitized data sample.