High-Precision Dlf-Based Locked Frequency Reference

48 HIGH-PRECISION DLF-BASED LOCKED FREQUENCY REFERENCE by J. Bareford This 10 MHz reference source for electronic clocks and laboratory equipment derives its stability of 3x10-8 from the powerful DeutschlandFunk (DLF) long-wave transmitter at 153 kHz. The accuracy of a frequency standard locked onto the carrier of a transmitter is, in principle, only dependent on the accuracy at which the carrier is generated. In the case of a number of stations transmitting in the long-wave range (50 to 200 kHz), the stability of the carrier is derived from an atomic clock with extremely high precision. Examples of high-stability stations are DCF77 (see Ref. 1), Rugby MSF, Droit- wich and DLF. Contrary to DCF77 and MSF, which are time-standard stations, DLF transmits an amplitude-modulated broadcast program. The stability of the daytime carrier at 153 kHz is 5 x10-"3 at a transmit power of 500 kW; that of the nighttime carrier is 5 x 10-12 at 250 kW. Fortunately, the transmitted signal is free fr...