A Phase-Locked Primary Frequency Supply for the L Multiplex

By O. P. CLARK, E. J. DRAZY, and D. C. WELLER The carriers and pilot tones of the L multiplex are all derived from a single source of 4 kc. The new primary frequency supply provides this primary frequency. It is designed to operate phase-locked to a pilot tone derived from an incoming carrier system and hence to have no frequency error with respect to that tone. The unit features a high degree of frequency stability, even in the absence of the pilot; it features more reliable performance and lower maintenance as well as marked size reduction compared with the older equipment. I. INTRODUCTION' In single-sideband suppressed-carrier transmission systems, of which the L-type multiplex is a modern example, it is necessary to supply, at each terminal, sequences of harmonically related carrier frequencies to power the various modulators, and also to provide line pilot frequencies for system regulation. Because the accuracy requirements for these frequencies are severe, it has proven most economical and technically satisfactory to derive them all from a single highly accurate and stable source which, in the case of the L-type multiplex, has been named the primary frequency supply. The means by which the ensemble of carrier and pilot frequencies is derived therefrom are described in a companion article.