A new one, Piet Lassche has this American Transmitter, it looks like a weather-forecast-balloon device, who knows more about this item?????
Hereby an answer and some pictures from South Africa, from Sten, ZS 2 CFC
Radiosonde T 435 is indeed used for weather...forecasting. The device is carried by balloon ( at this time hydrogen filled ) up to about 10 kms. As long as the balloon can be observed the wind direction at at that height the sonde is can be established. Because it transmits barometric data. Other data send down is temperature and humidity. There are many different designs, this old one is with tubes/valves. Some of those where dropped with a parachute from plane into the eye and or specific points of Hurricanes to get data to learn more about these winds.
It is quite possible that these devices have been used in Europe, not just Germany. I do have the Manual "Radiosonde AN / AMT - 4A " from which the attached pictures are. As you can see on your website is only the "Radio" part and not the sensor part shown. There are many types and makers for these Sondes. They are started from many key places 4 times or so a day to get a picture of higher up winds and conditions, which help in forecasting. This however means that they must have been made by the 100 thousands... I do have a couple of Sondes and allied parts , many - including the handbook come from : www.fairradio.com USA based-the worlds finest surplus...as they say