A narrowband version of the TACS 1G analog cellular radio technology developed for use in the United Kingdom. NTACS operates in the 900 MHz band, employs frequency modulation (FM), and supports 400 channels of 12.5 kHz. As an analog system, TACS derives channels using frequency division multiple access (FDMA) and bidirectional communications is achieved through frequency division duplex (FDD) with the downlink in the 860