NMT-450 is an analogue mobile telephone system, developed by the Telecommunication Administrations of Denmark, Finland, Norway and Sweden. The idea was to establish a compatible, automatic, public mobile telephone system in the Nordic countries.

NMT-450 mobile station signals can be found from 453 MHz to 457.5 MHz, base station signals from 463 MHz to 467.5 MHz. The frequency range is divided into 180 channels of 25 kHz each (channel 1 -180).

In areas with a lot of mobile subscribers, an extended band from 452.5 MHz - 452.975 MHz (mobile) and 462.5 MHz - 462.975 MHz (base) may be used as an option. The offset between mobile and base frequency is always 10 MHz.

Control messages (signals) containing system wide information, assignment, status and dialed number are exchanged between the mobile station and the base station.

All signals are transmitted at 1200 Bd FFSK with a center frequency of 1.5 kHz and a shift of 600 Hz.

An encoded NMT-450 frame has a length of 166 bits. Every frame contains 15 bits bit sync sequence followed by an 11 bits frame sync sequence. The last 140 bits contains the encoded message. In order to combat errors on the radio path, due fading and interference, an error-correcting code is used.

Today, NMT-450 is used in Sweden and a modified NMT-450 in Poland and Eastern Europe. More information can be found in the NMT DOC 450-1 / 450-3 specifications.