The N a t i o n a l Bureau o f Standards, i n cooperation w i t h t h e N a t i o n a l Oceanic and Atmospheric A d m i n i s t r a t i o n (NOAA), has been d i s s e m i n a t i n g a t i m e code referenced t o UTC(NBS) v i a two o f NOAA's g e o s t a t i o n a r y GOES s a t e l l i t e s s i n c e 1975. A review o f t h e GOES t i m e code system, t h e performance achieved t o date, and some p o t e n t i a l improvements i n t h e f u t u r e w i l l be discussed.The disseminated t i m e code i s o r i g i n a t e d from a t r i p l y redundant s e t o f atomic standards, t i m e code generators and r e l a t e d equipment maintained by NBS a t NOAA's Wallops I s l a n d , VA s a t e l l i t e c o n t r o l f a c i l i t y . I t i s r e l a y e d by two GOES s a t e l l i t e s l o c a t e d a t 7 5 O W and 135"W l o n g i t u d e on a continuous b a s i s t o users w i t h i n North and South America ( w i t h over1 apping coverage) and well o u t i n t o t h e A t l a n t i c and P a c i f i c ocean areas. Downlink frequencies a r e near 468 MHz. The s i g n a l s from b o t h sate1 1 i t e s a r e monitored and c o n t r o l l e d from t h e NBS l a b s a t Boulder, CO w i t h a d d i t i o n a l m o n i t o r i n gi n p u t from geographical l y separated r e c e i v e r s i n Washington, DC and Hawaii. Received t i m e code accuracies a r e t y p i c a l l y b e t t e r than 1 ms i f t h e u s e r o n l y a p p l i e s a c o n s t a n t c o r r e c t i o n t o compensate approximately f o r h i s geographical l o c a t i o n o r b e t t e r than 100 p s i f manual o r automatic c o r r e c t i o n s are a p p l i e d f o r p a t h delay u s i n g s a t e l l i t e p o s i t i o n d a t a encoded i n t o t h e GOES t i m e code s i g n a l s .Performance experience w i t h t h e r e c e i v e d t i m e codes f o r p e r i o d s r a n g i n g from several y e a r s t o one day i s discussed. Results a r e a l s o presented f o r s i m u l t aneous, common-view r e c e p t i o n by co-1 ocated r e c e i v e r s and by r e c e i v e r s separated by several thousand k i 1 ometers.Based on t h e general acceptance o f t h e GOES t i m e code, NBS and NOAA have r e c e n t l y extended t h e i r formal Memorandum-of-Agreement t o c o n t i n u e t h e GOES t i m e code o p e r a t i o n s f o r a t l e a s t an a d d i t i o n a l f i v e -y e a r p e r i o d ,

The Time and Frequency Division of the National Bureau of Standards has conducted an engineering study to determine the feasibility of using the GOES satellite ranging system for precise (0.1 microsecond, one-sigma) time transfer to a receiving-only timing site. The GOES satellite ranging system, termed a trilateration system, will accurately locate this satellite within some coordinate structure. The sources of time transfer errors have been studied in some detail.These errors can be caused by satellite location errors, ground station location errors, unknown delays caused by the troposphere, the ionosphere, and the various equipments. Simplified designs for an automatic and a manually operated timing site are presented. Some technical problems found in the associated equipment are discussed. The study indicates that a secondary, or slave site, clock could be synchronized to within 0.1 microsecond, one-sigma, of some master clock utilizing a one-way, or receiving-only system.

The Time and Frequency Division of the National Bureau of Standards produces the NBS time scales, AT(NBS), SAT(NBS), and UTC(NBS). These time scales are developed by utilizing the properties of the NBS frequency standard, NBS-III. The main byproduct of these time scales is the operational clock systems.These operational clock systems are used, among other things, to calibrate the clocks and secondary standards necessary for the operation of the NBS radio stations, WWV, WWVB, WWVL, and WWVH. These stations transmit SAT (NBS), UTC(NBS), and various tones, alerts, and corrections for time-of-day information.

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The Time and Frequency Division of the National Bureau of Standards maintains primary frequency standards, which provide a realization of the internationally-defined second, and two atomic time scales, AT(NBS) and UTC(NBS). AT(NBS) is dependent upon the primary frequency standards, an ensemble of commercial cesium clocks, and a computer algorithm to process the data. The UTC(NBS) scale is derived from AT(NBS) by the addition of small annual frequency adjustments and leap second adjustments to keep its time nominally synchronous with the international time scale UTC. The UTC(NBS) time scale is used to calibrate the clocks and secondary standards necessary for the operation of the NBS radio stations, WWV, WWVH, WWVB, and WWVL.These stations transmit various standard frequency and time signals throughout the world, and, in addition, provide certain official announcements such as geoalert warnings, marine weather advisories, and radio propagation forecasts.