Using thin membrane InP microdisc lasers heterogeneously integrated on a silicon on insulator (SOI) substrate having a broadband analogue modulation bandwidth of 11 GHz, analogue direct modulation with radio data signals (64 and 256 QAM, 20M symbols/s at 5 GHz RF carrier) is demonstrated. The demonstration shows the potential of the microdisc laser as a low-energy analogue optical transmitter with error-vector magnitude penalties of 3.6 and 4.2 for 64 and 256 QAM, respectively, and the low biasing currents for both DC (4 mW) and RF (0.1 mW) signals, which are compatible with signals and currents which can be supplied by a simple CMOS driving chip