German Automatic Meteorological Transmitter, WWII Tactical and Technical Trends, No. 16, January 14, 1943 (Lone Sentry)

This meteorological transmitter was found to be located in the open on land, and serves a purpose similar to the larger, floating meteorological stations known to be used by the enemy.

The full equipment comprises a complete low-power, short-wave transmitter, automatically operated by meteorological instruments, to record the temperature and pressure in the locality in which it is stationed. The times and periods of transmission are set on a master clock.

The transmitter is a Lorenz crystal-controlled, four-tube transmitter made in 1940, operating over two wave bands: 17.5 to 6.6 and 6.6 to 5.6 megacycles per second. The tubes are master oscillator, frequency-doubler, and two 15-watt output tubes, in what appears to be a push-pull circuit. Continuous wave or interrupted continuous wave can be transmitted when the transmitter is switched on by the clock mechanism. This transmitter is obviously a factory production and is well mounted in a tubular frame, but the whole is encased in a weatherproof container of doubtful efficiency and "workshop" finish. The clock unit was also in this container, but was sealed in its case with a waxed-wood cover and a waterproof packing.

The meteorological controlling unit is a Morse-sending device; the signals sent being altered by the positions of three contactors, and the contactors being moved by the meteorological instruments. In addition, a further contactor is hand-set, presumably to pick out the recognition signal of the meteorological station. The operating meteorological devices consist of a curved bi-metallic strip for registering the temperature, and two barometers, one with twin capsules (coarse reading), and the second with four barometric capsules (fine reading). It is necessary to provide two barometric devices in order that the full reading may be obtained. It is thought that the first instrument will transmit a signal indicating the nearest millimeter, and the second will provide the decimal part of the local pressure reading. The contactors, operated by a geared-up rack-and-pinion movement, are in the form of 10-finger stars with sharpened points, arranged around the circumference of a circle. The result of a change of temperature or pressure is to alter the position of these points relative to the axis of this circle. The rotor, or contact arm on which these contactors operate, consists of a sector-shaped piece, the circumference of which moves around the circle inscribed by the contactors. The sequence is that the sector first makes contact with the identification signal, then with the coarse barometer, the fine barometer, and finally, the thermometer contactor.

It should be understood that, according to the setting of the contactors, a different signal is picked up by the projecting fingers. Anyone receiving this signal can ascertain the position of the contactor, and hence the temperature or pressure at the moment of transmission, if the key of the coding on the rotor arm is available.

The clock is an elaborate mechanism for performing the simple task of making contact between two leads for the periods of transmission. It consists of an electrically wound clock which registers the time by means of a rotating disk, engraved with the 24 hours. The switch operating devices are secured by means of two thumbscrews around the periphery of this disk. The two leads, "shorted" by the clock, switch on the transmitter and meteorological unit. There are two batteries in the set: one a 24-volt, 69-ampere hour, low-voltage unit, contained in a weather proof metal case, 3 feet 6 inches by 1 foot square; the other, a high-voltage battery consisting of four 90-volt cells connected in series. The latter was of similar type and construction but of 11-ampere hour capacity.