"The 53.5-MHz radar of the Max-Planck-Institut für Aeronomie (SOUSY-VHF-Radar) was specifically designed for the study of the dynamics of the troposphere, stratosphere, and mesosphere including turbulence and other small-scale phenomena. Transmitter and receivers were designed for a pulse width and altitude resolution of the order of 75–150 m. Such high resolution corresponds to sampling rates of the order of 2 million complex samples per second. Maximum sensitivity calls for the use of coded pulse schemes (pulse compression). The digital decoding and processing requirements of such a high information rate are beyond the capabilities of a general purpose digital computer and demanded a special purpose preprocessor. A programable preprocessor was designed and built, and it is the subject of this paper. It can decode an arbitrary sequence and perform coherent integrations for as many as 1024 altitudes. The coherent integration reduces the data rate into the computer to reasonable values. Also, by performing the coherent integration before decoding (they are linear operations and can be permuted), the necessary decoding operations in the preprocessor are reduced by 2 orders of magnitude. The master controller for the device is programed by a 1024 4-bit instruction PROM. There are 16 different instructions allowing the necessary flexibility for different code and sampling schemes. The transmitter and analog-to-digital converter are also controlled by the same device. Stratospheric and mesospheric echoes obtained with the help of this device are presented for illustration. The detection of layers as thin as 150 m or less at both stratospheric and mesospheric heights justified the efforts to achieve the maximum resolution possible."
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