MUSEUM "WAALSDORP"

The meteorograph contained a bimetallic thermometer, a hair hygrometer and a Bourdon type barometer, each moving a rolling wiper over a series of contacts. These contacts were connected to brushes sliding over a drum rotating at one revolution per second by a tiny electric motor and a worm gear. The drum made of isolating material was on the outside covered with a conducting pattern providing a Morse coding.

This comprised for the thermometer a set of four different Morse letters corresponding to four consecutive contacts, cyclically repeated on each four following contacts. In the same way the hygrometer had two sets of codes of 3 letters corresponding to 3 consecutive contacts. The change from one set to the other was caused by a barometer in passing a contact.
The output of the code drum acted as switch between the battery and a vibrator/ transformer supplying power to the anode of a simple six meter (50 MHz) triode transmitter. The latter was at the same time amplitude modulated with the 600 Hz vibrator frequency. Thermometer and barometer were calibrated while mounted in the meteorograph by bringing the package in an evacuated and cooled tank. The hygrometer was tested separately. The total weight of the meteorograph with one flash-light dry battery of 4.5 volt was 0.465 kg, sufficient for ascents up to five km. For greater heights two batteries were installed, one for anode- and filament-supply and the other for the motor, which increased weight to 0.585 kg. These weights belonged to the lowest anywhere for comparable arrangements.

Signal reception took place with a simple super regenerative receiver allowing distances up to hundred kilometers. Also a special directive antenna was developed to additionally determine the chart angle (azimuth) of the transmission. Registration and data extraction following reception was taken care of by the Military Weather Forecasting Service of which no technical details are available.