The speaking ballon

is a project to show pupil the world of ham radio. It is invented by AATiS e.V. a German club that has many activities in this direction.


The idea is to build payloads for weather ballons with ham radio functions. Different steps - from an easy voice memory connected to a 2m-tx to a 13cm-ATV-tx - were planned and realized in the last 5 years. To follow the flight in position and height a GPS-Rx is on board, the data is sent as AX.25-UI-packet radio-frames and in some cases as voice.

The interesting scenario and the collected data are the connection the pupil in schools.

History of our Speaking Balloon

In 1995 we (Pico, DF8AK and me) met Wolfgang, DL4OAD, the president of AATiS. It was on the Interradio, a ham fair in Hannover and I've just bought my Magellan Trailblazer GPS-Rx. Wolfgang told us about the project and we were interested to develope a speaking pay load.

In 1996 our first model started, but with many problems.

So we decided to redesign the concept and to use a PCB that were produced by a commercial supplier. In 1997 the second launch were made by Mike, DF2OK and it was a success (very good report of this launch - German). Two further starts followed - the last one with a GPS-Rx-problem: No more position information from the Rx.

In 2000 there was the last launch. With a software update to detect the 'sleeping' GPS-Rx and to restart the Rx in this case and some other security features the last flight was a complete success and a nice present for the work.

Technical details

The circuit of the balloon is based on the well known TNC2C, invented by Landolt Computer in 1986 and copied several times since then. We added five parts:

This board is the processing part of the ballon. The weather sensor is a seperate circuit, converting the information of a VAISALA 80-sensor into a NMEA-like serial datastream. This was developed by August, DK5UG. The 2m-transmitter is a special development of GŁnther, DF5FC, to ensure a stable signal in extreme low temperatures. And last, but not least, a Microtracker GPS Rx, with a ceramic patch antenna gives us positional information. All of these external components were used in other balloon projects also.

This is a block diagram of the complete balloon equipment:

still to draw...

As you can see, the hardware is not only able to send, all neccessary stuff for receiving speech or Packet Radio is on board. If you are interested in the circuit details, you can download a picture of it. An eagle-file and some written documentation about addresses, jumper and connectors is also available, please contact me.


Like the hardware, the software is based on TheFirmware for TNC2. You can find an actual version of this on the Nord><Link-Homepage. I took an older version and removed all the stuff concerning the userinferface to gather some EPROM-space for additional functionality.

I added some modules:

 I'm almost sure there is no use in offering you the source of the balloon software. There is no external and only small internal documentation, but, ok, here it is. (later)