 The OFDM guard interval for TM I is 246 microseconds, which means that the overall OFDM symbol duration is 1.246 milliseconds.The guard interval duration also determines the maximum separation between transmitters that are part of the same single-frequency network (SFN), which is approximately 74 km for TM I.

OFDM allows the use of single-frequency networks (SFN), which means that a network of transmitters can provide coverage to a large area – up to the size of a country – where all transmitters use the same transmission frequency.Transmitters that are part of an SFN need to be very accurately synchronised with other transmitters in the network, which requires the transmitters to use very accurate clocks.