This report describes the interfacing and programming of a minicomputer for Doppler spectrum analysis. The interfaces include analog-to-digital converters for data input and digital-to-analog converters for display of the Doppler spectra on an XY oscilloscope. These interfaces are contained in the computer chassis which has the dimensions of a suitcase. The software that is included in this report is specifically written for 64 point Doppler spectra. The Fast Fourier Transform algorithm is used in the analysis, and the time required to transform a 64 point array is 23 milliseconds. Control of the spectral analysis program is by means of 16 data switches on the front panel of the computer.

A portable 50 MHz transmitter capable of 15 kW peak rf power output at up to 5 percent duty cycles is described. The transmitter and a system synchronizer, also described, are combined with a frequency-coherent receiver, an on-line minicomputer processor with oscillograpic display, and a novel collinear antenna to provide a highly portable VHF Doppler radar system. The system, complete with 5-degree azimuthal beamwidth antenna, weighs about 250 kg, and can be installed in remote locations in a few days. It has been used successfully in studies of equatorial and auroral ionospheric irregularities during the past several years.

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