This is a radiosonde used by the German army.
It is important for the field artillery to know the air pressure in the atmospheres.


Radiosonde that measures both pressure and temperature.
Will try to find out how this works.
The tube on the top is the temperature sensor.


The radiosonde lay in the original box.
Original advertising from 1941 are used as packaging.
Here is also the original calibration documents..


Have here removed the lid.
Triode tube is mounted inside the transmitter coil.
Metal Box is for batteries.
Two 1.5Volt batteries deliver 3.0 volts to the transmitter..


Now beginning to understand how the radiosonde works.
Temperature sensor is made of bimetal.
The movements of this is connected to a butterfly capacitor.
This changes the transmitter frequency.


In this picture you can see both the barometer and temperature gauge.
Here is also the calibration document for pressure measurements.
Pressure measurement is designed as on my second radiosonde.
Transmitter signal is interrupted for a short period at the pressure in the calibration document.


It is both pressure and temperature calibration documents.
The users of these radiosonde used this calibration documents to get the actual measurements data.
Disruption of radio signal measures the pressure.
The frequency of the transmitter measures the temperature.

I have here drawn electrical schema for the radiosonde.
Power is two 1.5Volt battery's.
A vibrator generat 100 volts AC at 1000Hz.
This will turn on the tube on each positive half period.
This will also generate a AM modulation tone.
This is IMPORTANT for the radio operator whichwill follow the frequency of the radiosonde.

The barometer is connected to the tube anode.
The signal will be grounded at each of the 16 pressures described in the test document.
Radio operator must log the exact time for this interruption.

The butterfly capacitor is connected to a bimetal temperature sensor.
When the temperature goes down, the butterfly capacitor will rotate.
From minimum two maximum frequency in 30 degree rotation. On 60 degree the frequency is minimum.
Down to-70C the capacitor will rotate many turns.
Radio operator must follow and log the exact time for this frequency variations.

Test documents are used to get temperature and pressures data in a normal form.