National time and frequency standards of Finland

National time and frequency standards in Finland are based on Loran-C phase-locked clocks. The Loran-C clock comprises a high-stability crystal oscillator (HP 105 or equivalent), a Loran-C receiver, a digital clock, and a specially constructed digital phase controller. There are 10 clocks in continuous use in Finland, one in Sweden, and one in Norway. In Southern Finland the clocks utilize a transmission of 7970 W (Sylt) and in Northern Finland that of 7970 X (Bo). The time constant of the digital phase controller is about 1 hour. Thus short-term fluctuations of the receiver phase are damped. Comparisons with rubidium and cesium clocks show that the standard deviation of the phase of the crystal oscillator is from 0.1 to 0.3 μs. The short-term (1 hour) frequency stability is better than 2×10−11. In addition, Loran-C is regularly compared with other time signal transmissions. Several clocks utilizing the time code of DCF 77 (West Germany) have been constructed. The accuracy of these clocks varies from 0.1 to 1 ms depending on their construction. The reception of Soviet TV (Tallin) synchronization pulse was started in January 1978. Initial results indicate the standard deviation of UTC(Helsinki)–UTC(Tallin) to be less than 1 μs. This project is being carried out in cooperation with Soviet scientists.