Nationwide Precise Time and Frequency Distribution Utilizing an Active Code within Network Television Broadcasts

Abstract

Because of the increasing interest in time and frequency dissemination via television signals, the National Bureau of Standards (NBS) has sponsored an experiment using an active time and frequency code transmitted on a U. S. television network encompassing nationwide coverage. Some history of the project is given. The format of the television code and the equipment necessary to generate and decode the transmitted information are discussed. Statistical results of system stability from New York City, New York, to Boulder, Colorado, and to Los Angeles, California, are presented, and comparisons are made with earlier observations using the passive line-10 television time synchronization technique and the 3.58-MHz color-burst frequency reference used for colorcasts. Analysis of the frequency-transfer capability is presented, and the ability of a phase-locked oscillator to lock to the code's frequency reference is discussed. With the decoder's oscillator in a locked condition, plots of phase with respect to time, time domain stability using the Allan variance, and spectral noise reveal that the system permits calibration of a remote standard to one part in 1011 within one-half hour. Long-term stability (several days) is typically a few parts in 1012. Using an active time code, short-term stability is governed to a noticeable degree by the television industry's standard video format. Finally, a schematic diagram, with discussion, outlines how time-of-day information can be extracted from the television code used in this experiment.