The Nonlinear Theory of Electric Oscillations

The progression of developments in crystal frequency standards is traced through the last half century. The paper emphasizes the underlying technical changes and innovations that have driven the remarkable progress, while keeping in mind the contribution of the great body of information that was already available at the beginning of the period. The paper gives a treatment of the progress of ovenized crystal frequency standards from the early vacuum tube days through implementations using transistors, LSI, and hybrid construction. The progression of TCXO developments is also covered including analog thermistor temperature compensation, digital compensation, and techniques using micro-computers, and self-sensed oscillators.

Fifty years of progress in quartz crystal frequency standards

Improvements in astronomical time measurement techniques and in the definition of time have kept pace with developments in frequency standards. Quartz crystal frequency standards are described, including Essen rings, bars, GT-cut plates, and contoured AT-cut plates. Stable oscillator circuits for quartz-crystal frequency standards are described, including the Meacham bridge-stabilized circuit, the Gouriet-Clapp circuit, and the Lea quartz-resonator-servo circuit. A discussion of the present status of atomic and molecular frequency standards includes the ammonia absorption cell, ammonia oscillator (MASER), and cesium atomic-beam apparatus. Instrumentation for precision frequency measurement is outlined, and a current listing of standard-frequency broadcast stations is included.

Frequency and Time Standards

The negative-resistance oscillator possesses many advantages over the ordinary triode feed-back types. The most common of negative-resistance oscillators, the dynatron, has not been generally adopted owing to its dependence on secondary emission, an unsteady property. The retarding-field negative-transconductance oscillator possesses the advantages of the dynatron without its disadvantages. This type of oscillator is discussed from the practical standpoint, the theoretical treatise having been given in a previous article. The oscillator will generate sinusoidal oscillations of any frequency from the lowest audio to 60 megacycles by simply changing the tuned circuit constants. It will function with direct plate and anode voltages of 2 and 4 volts, respectively, or 50 and 200 volts, respectively, or any intermediate values. An alternating-current output of a fraction of a volt to over 20 volts effective value is obtainable across the tuned circuit. The simplicity of construction and operation and the assurance of constant performance make this type of oscillator a valuable addition to the laboratory.

The Transitron Oscillator

Trade-Offs in Oscillator Phase Noise

A method is described for obtaining a convenient low frequency from a high-frequency standard by means of harmonic control of distorted wave oscillators (multi-vibrators). In the equipment described two such oscillators are employed, for convenience in arriving at a harmonic series of frequencies, based on 10-kc fundamental, as well as a frequency of 1 kc for operation of the clock motor, from a standard frequency of 50 kc. The conclusions based upon an experimental investigation of harmonic control of the distorted wave oscillators are given. Representative curves of the variations in frequency of the 50-kc standard for 10-day intervals are shown.

J.K. Clapp

Papers

A Convenient Method for Referring Secondary Frequency Standards to a Standard Time Interval