This paper presents a status data transmitting system suitable for vessel monitoring. The system consists of four main parts, which are a frequency synthesizer, a horn antenna, a status data module and a power amplifier. The proposed frequency synthesizer can flexibly change the frequency in a wide range (from 600 MHz to 4.2 GHz) and the output power (from -6 dBm to -3 dBm). By using the phase-locked loop, the synthesizer’s stability over temperature and tolerance are comparable to temperature compensated crystal oscillators (TCXO) that is about +/- 3 ppm. Moreover, phase noise performance of the synthesizer is less than -90 dBc/Hz at 1 KHz and -100 dBc/Hz at 100 KHz. The impedance bandwidth of the horn antenna can be controlled by using the beveling technique. The status data module packs information of the identification, longitude, latitude, and state of the vessel into data frames. FSK/MSK/GMSK schemes were used to modulate the data. The power amplifier provides 130 W output power at S-band. The fundamental characteristics of the implemented transmitter have been measured and verified.