The STS1TX is a very low-power RF transmitter intended for RF wireless applications in the sub-1 GHz band. It is designed to operate both in the license-free ISM and SRD frequency bands at 169, 315, 433, 868, and 915 MHz, but can also be programmed to operate at other frequencies in the 300-348, 387-470, and 779-956 MHz bands. The air data rate is programmable from 1 to 500 kbps, and the STS1TX can be used in systems with channel spacing of 12.5/25 kHz, complying with the EN 300 220 standard. It uses very few discrete external components and integrates a configurable baseband modem, which supports data management and modulation. The data management handles the data in the proprietary fully-programmable packet format, and also allows the M-Bus standard compliance format (all performance classes).

An AES 128-bit encryption co-processor is available for secure data transfer. The STS1TX supports different modulation schemes: 2-FSK, GFSK, OOK, ASK, and MSK. Transmitted data bytes are buffered in FIFO (TX FIFO), accessible via the SPI interface for host processing.