Frequency standards

Today, clocks and oscillators are vital devices in countless scientific and technological applications, encompassing sophisticated tests of fundamental physical theories on one side as well as synchronization of communication systems on the other one. There are by now many diverse realizations, ranging from common wristwatch quartz oscillators to ultrarefined primary frequency standards. In spite of this wide assortment, both in terms of cost and performance, all oscillators can be characterized within the same formalism. This is also true for time and frequency dissemination. Indeed, transmitting time over dial-up telephone lines with an uncertainty of about 1 ms hinges on the same principles that are the foundation of the 1-ns-uncertainty, satellite-based time broadcasting. Let us start by summarizing a few considerations scattered in previous chapters and putting some order in the nomenclature [650].