We have not yet been able to come up with working two way communications between the balloon and the ground station. Current practice is to transmit from the balloon only, using 50baud RTTY on 434.075MHz USB (upper side band) at a maximum power of 10mW. Rather surprisingly we have managed to receive data over 500km despite the low power of the existing system.
We want the element14 community to develop a project that will enable reliable two way communication, line-of-sight, over a distance in excess of 50km. The communication requirements are very low in terms of the volume of data that needs to be sent and received and may be as low as one character per second. Ideally the project would interface with a micro processor using one of the common interfaces such as two wire (I2C), serial peripheral interface (SPI) or one wire.
The project will need to observe some constraints, primarily for safety:
- The total weight of the project CANNOT exceed 1kg. This will give a total weight of 1.5kg for the payload.
- Any exposed parts will need to be protected to prevent injury should the payload hit something on its return to ground.
- Radio frequencies must be within the Ofcom rules for aeronautical use. Pages 58,59 & 60 of this document cover the regulation of aeronautical frequencies.
There are also issues around crystal stabilization due to temperature variation and some consideration of this needs to be taken in to account.
Developing a solution with a low cost of production will also be a key factor in selecting the winning design.
Remember, to enter the Icarus design challenge simply submit your circuit design and detailed specification via private message to RHarrison1971 by 17th February 2012. Robert will announce the winner in this group by 2nd March 2012. element14 will then forward the components required to build the winning solution to allow the winner to produce a working prototype ready for launch.
Good luck!