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HEWLETT-PACKARD
JOURNAL
T E C H N I C A L I N F O R M A T I O N F R O M T H E - d p - L A B O R A T O R I E S Vol. 1 1 No. 3-4
'UBLISHED BY THE HEWLETT-PACKARD COMPANY, 1501 PAGE MILL ROAD, PALO ALTO, CALIFORNIA NOV.-DEC, 1959
A New Clock for Improving the Accuracy
of Local Frequency and Time Standards
In line with the continually advancing ma to reduce comparison error, it should be noted
turity of the electronics field as a whole, the that the accuracy of WWV carrier and time
portion of the field concerned with frequency signals is currently 2 parts in 10'°.
control has made significant forward strides in COMPARISON CONSIDERATIONS
recent years. As a result, high-precision fre When calibrating a local standard against
quency standards employing quartz resonators the transmissions from a standard radio sta
presently achieve stabilities of a part in 109 tion such as WWV or WWVH, the necessary
per day or better, while atomic standards ex comparison can be made by either of two basic
hibit accuracies of one or two parts in 1010. methods. The more widely used but less pre
In order to operate a frequency standard at cise method is the direct frequency comparison
or near presently attainable accuracies, it is in which the local standard frequency (or its
necessary to minimize the error that may occur harmonic) is directly compared with the car
in comparing the standard with the primary rier frequency of the received standard trans
signal against which the standard will be cali mission (or its harmonic). In this method the
brated. In precision work such comparison maximum accuracy achievable is determined
error should be minimized, not only so that by the uncertainty that variations in the trans
the uncertainty in the standard will be re mission medium introduce into the transmis
duced, but also so that the drift characteristic sion. For the usual case of sky-path transmis
that all quartz standards exhibit to a greater sion, the frequency, as received, can be differ
or lesser degree can be determined and moni ent from that transmitted by up to several parts
tored with maximum accuracy. As an indica in 10' because of ionosphere movement and
tion of the degree to which it may be desirable other effects. Although special techniques such
Fig. 1. New -hp- Model 113 AR Frequency Divider and Clock simplifies Fig. 2. Oscillogram of WWV seconds pulse
intercomparison of local frequency standards with national standards ("tick") as obtained using new Clock in
via broadcast time signals and increases resolution with which such typical set-up. Sweep time is I millisecond/
comparisons can be made. Use of instrument with suitable local fre cm, indicative of high resolution of time
quency standard also permits time to be kept on a local basis to within comparison that Clock permits.
a millisecond. Instrument is fully transistorized and designed with fail
safe provisions.
P R I N T E D I N U . S . A . C O P Y R I G H T 1 9 5 9 H E W L E T T - P A C K A R D C O .