Today the software and telemetry team has performed the range test.
Strategic points in the area of Würzburg have been approached, which have a direct visual connection to the university library. The Dummy Seeds, which consist of an Arduino, a Wireless SD Shield as well as an XBee including antenna were started. The functioning of the dummy seeds is identical to the later heartbeat mode of the SpaceSeeds, which is intended to find the seeds after the landing.
Then the incoming signal strength, called RSSI value, is read from the XBee with the range tester, also
an Arduino with Wireless SD Shield, XBee and an I2C LCD display.
In this test, a certain byte string is sent from the range tester or “SpaceSeed Search Device” to the
address of a specific dummy seed. This checks whether the byte sequence corresponds to the
expected sequence and if the sequence matches it sends a certain byte sequence as confirmation.
The Search Device waits for this response and checks for the response and then uses an XBee
function to output the RSSI value. Request the RSSI value and then print it on the display.
We reached line-of- sight distances of 3,5km and 4km, where we got a signal strength as we expected in our link budged calculation beforehand. We were also able to reach 8km line-of- sight, but with this distance there were no signal anymore. Although the datasheet of the XBees we use say, that we can reach 8,4 kilometers, there are many factors which has to be considered. For example the line-of-sight were located over the Würzburg city, which means we have a small amount of “smog” (okay, to be honest, Würzburg is not really dirty, but small amounts are a factor) and secondly, the transmission tower “Frankenwarte” is with some kW sending power really a disturbance. At the End, the test can be seen as success, because up in 80km high we will have definitely better conditions!