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An improved sweep-frequency ionosphere recorder was needed to carry out the expanded program of observation planned for the IGY. The resulting equipment included improvements in output power, receiver sensitivity, purity of output signal, and other details, over earlier equipments. The basic principles of operation are described and the transceiver-type of circuitry explained. The operating characteristics are: frequency range, 1-25 mc; output power, 10-30 kw peak pulse power; pulse length, 50 Â¿sec; repetition rate, variable from 10-70 pulses per second. An elaborate control and programming system is provided which can be used to operate the equipment on an unattended automatic basis. The "virtual height" of the ionospheric layers, as a function of frequency, is recorded on photographic film by two camerasÂ¿a 35-mm uniformlymoving-film unit, and a frame-by-frame 16-mm camera, which produces time-lapse motion pictures of the changes which occur. A brief history of the development of the sweep-frequency recorder technique is given.