Master thesis : Pre-study and development of a 5 GHz FSK telemetry transmitter

Abstract

This thesis is conducted within the company Thales. The objective of this work is the study and development of a telemetry transmitter module compatible with the IRIG 106 telemetry standard and operating in the C-band frequency range. Telemetry is an essential element for the validation of system performance during flight for the Laser Guided Rocket (LGR) from Thales. The first part of this work introduces the principles of telemetry and digital communications as well as the IRIG 106 telemetry standard, which is widely used in telemetry applications to ensure interoperability between different equipments and systems. Two modulation schemes recommended by this standard are presented and compared: PCM/FM and SOQPSK-TG. The PCM/FM modulation is chosen for its simplicity of integration with the existing ac quisition system. However, SOQPSK-TG offers higher spectral efficiency, a characteristic often desired for applications requiring higher bit rates. The modulating signal containing the data to be transmitted is a 2 Mbps bitstream encoded as NRZ-L. The implementation of FM modulation is achieved using a Phase-Locked Loop (PLL), with direct modulation of the Voltage-Controlled Oscillator (VCO). The FM modulation is first implemented using the evaluation board of the selected PLL. The modulating signal is injected through a compensator circuit inside the loop filter of the PLL in order to achieve the required frequency deviation for the FM signal. A PCB has also been designed to integrate the PLL with other components such as the microcontroller used to program the registers of the PLL. At this stage, no power amplification stage has been designed. The frequency deviation observed at the spectrum analyzer is ±720 kHz which is close to the optimum frequency deviation recommended by the IRIG 106 standard. A Software-Defined Radio (SDR) is also used to record and demodulate the FM signal. Al though this approach was not initially planned within the scope of the project, it provides promising results for future reception systems. The demodulation correctly reconstructs the baseband signal. However, data recovery through clock recovery is still not fully functional and still requires further work. Only the amplification stage needs to be implemented to use the transmitter in real flight tests. A study on the available resources to power this amplification must be conducted first. The introduction of SDR opens the way to the research and development of a reception solution fully based on SDR instead of the COTS receivers.