Abstract :
Equipment has been constructed at the National Physical Laboratory for the automatic measurement and recording of the standard frequencies transmitted by MSF, Rugby, on 60kc/s, 2.5, 5 and 10Mc/s, and also the carrier frequency of Droitwich, 200kc/s. For the latter and MSF 60kc/s, the methods of measurement are an extension of those already well established for the intercomparison of the N.P.L. frequency standards. The standard deviation of measurements lasting a few seconds is 2¿3 parts in 109 for MSF 60kc/s, and 3¿4 parts in 109 for Droitwich. Measurements of the phase of the 1c/s pulse modulation on MSF 60kc/s can be made with very high precision. In daily comparisons, the scatter of a group of 60 readings does not usually exceed 30microsec. By a process involving frequency changing by continuous phase shifting, the received frequencies of MSF 2.5 and 5Mc/s are recorded on a frequency meter of range ±1c/s, the discrimination being 2 parts and 1 part in 108 at these frequencies, respectively. The records obtained show well-defined diurnal variations on 2.5Mc/s, particularly at sunrise, where the deviations may amount to several parts in 107. The received frequency of 5 Mc/s is subject to continuous variations over a range of about 1 part in 107 during daylight hours; in darkness larger changes are recorded.
