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


A balloon is used to lift the radiosonde into the atmosphere.

Here is a complete radiosonde in the box. Antenna and calibration data are included.

Serial number: 13459

Here is the place for the anode battery.


To the right, barometer and antenna.
To the left, transmitter with the KC3 tube.
In the middle, here is the place for the heater battery.

An instrument is connected to the measuring instruments shaft.

I have here removed the barometer and connected power.
The transmitter worked fine right away.
Voltage is 2 Volt to the heater and 90 Volt to the anode.
I don’t know the original voltage used.
The transmitter worked fine also with 1.5V heater and 60 V anode voltages.
Output voltage to the antenna is 70V RMS.
Frequency out was 2117 KHz on serial number 13459.
My other radiosonde, serial number 6982 had the frequency 1869 KHz.

Here is the barometer. An instrument shows the air pressure.
0 is normal pressure at ground.
360 are vacuum.

Her we can see the measurement system.
The instrument rotates 360 degrees from normal pressure to vacuum.
An isolated wheel is connected to the same shaft.
On this wheel we have 18 metal bars.
A small wheel connects the bars to the transmitter.
This system connects the antenna to ground.
When the air pressure move one of the bars to the small wheel the RF
output is switched of.

Each radiosonde had a calibration chart.
Here we can see the pressure for each of these 18 bars.
When the radiosonde was lunched, a radio receiver at ground was tuned to the
actual frequency. Optical instrumentation is used for detection of the position
of the radiosonde when the signal is turned off by the bars.
Then they can use the air pressure date for calculating exact
data for the artillery.

LA8AK's shema.

Here is my schema.
How this radiosonde transmits the pressure data has been a mystery for many collectors.
You can read about how it works here.