The current version of the on board communication system is based on the CC1120 communication chip. The main reason for selecting this chip is the fact that it has been employed successfully in previous missions. Additionally its basic characteristics (identified here and applicable for our mission) made it a powerful candidate for the final system:
- Frequency range 402 MHz – 470 MHz.
- True single chip UHF RF transceiver.
- Very few external components required.
- No external IF filter needed.
- High sensitivity (up to -118 dBm for a 12.5 kHz channel).
- Programmable output power.
- Low current consumption. (RX: 19.9 mA)
- Digital RSSI and carrier sense indicator.
- Data rate up to 153.6 kBaud.
- OOK, FSK and GFSK data modulation.
- Programmable operation frequency and AFC may easily handle temperature and Doppler frequency shifts.
A low power MCU (STM32F4) will support the communication protocols especially AX.25 which is the preferred standard for this mission.
The employment of two identical communication systems, one as main, and the other as backup, was investigated, but deemed unfit for the mission profile. The increased weight, energy dissipation, space and complexity of the double system was weighed against the increased reliability of a redundant communication system.
There would be two dipole monopole antennas on the satellite. The lengths of the antennas are selected based on the radio frequency wave length.
- For the downlink data: 1* 180 mm long UHF antenna of 433 MHZ frequency
- For the uplink data: 1*610 mm long VHF antenna of 144 MHZ frequency
- The modulation type for uplink would be FSK
- The modulation type for the down link would be FSK
- The frequency for the uplink would be 144 MHz
- For the downlink 433 Mhz would be the selected frequency (actual frequency will be announced soon)
- The communications subsystem will support the AX.25 protocol
The Antenna Deployment System will be located in +Z face of CubeSat and consists of the two aforementioned monopole antennas (180mm UHF and 610mm VHF ), a PTFE antenna spooler hinged and the Dyneema metling line deployment system. A small amount of current will pass through the wire that will provide all the necessary heat to melt it and release the antennas. The antennas will be deployed with their own spring force.