To test UKHASnet network in the air on a balloon, to be launched on a latex balloon and act as a repeater for ground stations. To test range and whether it is possible to uplink data to the airborne node.

• LPC810 ARM Cortex-M0
• RFM69HW
• NCP1402 Step Up
• 2x AA Lithium Energizers
• 868Mhz Dipole antenna

Using latest LPC810 code reporting onboard radio temperature, RSSI of the last packet received and baseline RSSI. Packets transmitted every 30 seconds, in between device is listening for incoming packets.

BALL1 was kindly launched by Steve Randall from Elsworth in Cambridgeshire. Launched with a backup 434 RTTY tracker on a Pawan 2000g Latex balloon with an ascent rate of approximately 2m/s and ascending to a maximum altitude of 32986m before descending by parachute. At the launch site was a UKHASnet gateway SR0 repeating at 50mW (old code) with a 1/4 wave antenna positioned on a car roof. The balloon was tracked on 434Mhz throughout the flight and landed in some trees in Suffolk where it was recovered.

• BALL1 repeated packets from SR0 up to an altitude of 558m
• On the ascent it downlinked packets up to an altitude of 16952m.
• Initially all packets were via SR0 however it managed to be received by DB02 eight times.
• On descent DB02 managed to get a packet at 20774m and SR0 at 5158m

A selection of packets during the flight

Reviewing the data it appears that the node worked well on the ground and worked during the early flight, it also worked on the late descent and was fully functioning when recovered. It managed to get 2 packets through during the middle (high altitude) part of the flight suggesting that it was running throughout (confirmed by Ron(G8FJG) who was able to tune in with an SDR to the signal). It would have been expected that the node would have performed better as it climbed due to improving line of sight however we did not see this.

Looking at the data received it appears that temperature may have had a big influence on the radio modules performance - we were only able to get packets where the onboard temperature was greater then -10C. If the radio module got too cold its crystal would drift which would affect both the frequency and the data rate. There would be a degree of flexibility to allow for a certain amount of drift but its unlikely that these cheap modules would have been tested to such an extreme.

Reviewing the RSSI graph as the node did not repeat any packets after 558m altitude both RSSI1 and RSSI2 during the flight measured noise floor. There is an obvious jump in the noise floor which occured straight after launch - this is most likely the fact that the node can 'see' more. The noise floor didn't change much during the flight itself which should lend itself to hopefully receiving packets in the future.

• The modules are temperature sensitive and so will benefit from being kept at a more stable temperature. This could be achieved either by replacing the crystal or a DIY crystal oven using the onboard temp sensor and a resistor heater controlled by PWM.
• Worthwhile tracking the nodes signal on a SDR to ensure that it still transmitting.
• The nulls from the dipole may have had an impact on receiving on the ground as the balloon did not travel far. May benefit from other designs.
• Appears that you need about a 5deg elevation for telemetry (not as good as RTTY on 434Mhz)
• Need more ground nodes.
• There were a few packets received by 2 ground stations so if we can improve uplink capabilities it would be possible to make a link between 2 networks.

• CSV of Packets