In GSM cellular networks, an absolute radio-frequency channel number (ARFCN) is a code that specifies a pair of physical radio carriers used for transmission and reception in a land mobile radio system, one for the uplink signal and one for the downlink signal.
One such example is the TETRA system that has 25 kHz channel spacing and uses different base frequencies for numbering.
Together with the time-based component (TDMA — time-division multiple access) the physical channel is defined by selecting a certain ARFCN and a certain time slot.
This makes it more tricky to correlate the ARFCN strictly to a pair of frequencies, you need to know the specifics of the system.
Also the duplex spacing is generally 10 MHz in TETRA although other versions are available for certain applications.
In UMTS for 3G and 4G mobile telephone systems, ARFCN is replaced with UARFCN and EARFCN which are simpler and always has a direct relation between the frequency and the channel number.
In many countries in Europe there is a standardised set of frequencies used for blue light services i.e. the police, firebrigade, rescue and so on.
This set of frequencies correspond to ARFCN with a base of 300 MHz and an offset of 12.5 kHz.
Where: The range of frequencies used in these tetra systems are defined by 380-385 MHz for the uplink (mobile to radio base station) paired with 390-395 MHz for the downlink (radio base station to mobile).