Satellite controlled digital clock system

• US 4,014,166 A
• Filed: 02/13/1976
• Issued: 03/29/1977
• Est. Priority Date: 02/13/1976
• Status: Expired due to Term

• Current Assignee: THE GOVERNMENT OF THE UNITED STATES OF AMERICA, AS REPRESENTED BY THE SECRETARY OF COMMERCE
• Original Assignee: THE GOVERNMENT OF THE UNITED STATES OF AMERICA, AS REPRESENTED BY THE SECRETARY OF COMMERCE
• Inventors: Davis, Dicky D., Cateora, Joseph V., Hanson, D. Wayne
• Primary Examiner(s): Jackmon, E. S.
• Application Number:
  US05/657,918
• Time in Patent Office: 410 Days
• Field of Search: 58/24-26, 340/147, 340/163, 343/225
• US Class Current: 368/28
• CPC Class Codes: G04R 20/06 Decoding time data; Circuits therefor
• CPC Class Codes: G04R 40/02 by phase locking

Abstract

A method and apparatus are provided for maintaining and correcting a time ference in a satellite controlled digital clock system. A time code message including time-of-year information and satellite position information is transmitted in a data stream from a transmitter on earth to a satellite orbiting the earth to be relayed back to receivers located around the world. The data is transmitted at a precise data rate. According to the invention, a local clock oscillator is phase locked with the precise data rate, thereby providing the clock system with time-of-year information by counting the pulses produced by the local oscillator. At the same time, the digital clock system assembles the time code message from the received data stream and compares the message with the time accumulated by counting the pulses produced by the oscillator. After a predetermined number of errors are detected by such comparisons, the clock system resets itself to coincide with the received time code message. If transmission of the time code message is interrupted, the clock continues counting pulses produced by the local oscillator and thereby continues keeping time undisturbed. In a preferred embodiment, the digital clock system is implemented with a firmware programmed micro-computer and the time-of-year and satellite position information is displayed on light emitting diode digital displays.

Claims

1. A digital clock system in which a data stream is transmitted at a precise data rate, the data stream comprising a plurality of contiguous data records, each data record comprising a plurality of data blocks, each of said blocks having a data synchronization segment and a message code segment, the message code segments within a data record forming a time code message and said message including a message synchronization portion and a time-of-year portion, said clock system comprising:

receiver means for receiving the transmitted data stream;

a clock means for generating clock pulses at regular intervals;

phase lock loop means for phase locking said clock means to the precise data rate of said data stream; and

logic means for detecting the data synchronization segment of a data block so as to determine the position of each following message code segment in the received data stream, for detecting the message synchronization portion of the time code message so as to determine the beginning of the time code message, for assemblying the complete time code message from the individual received message code segments, for keeping time by counting said clock pulses, for comparing each complete time code message with the time represented by said counted clock pulses so as to provide a determination of whether said time coincides with the complete time code message, and for correcting the time represented by said counted clock pulses so that said time coincides with the complete time code message, responsive to a predetermined number of determinations of non-coincidence between said time and said complete time code message.

2. A digital clock system as claimed in claim 1 wherein said system further comprises display means for displaying the time represented by said counted clock pulses.

3. A digital clock system as claimed in claim 1 wherein the time code message further includes a satellite position portion and said system further comprises further display means for displaying the satellite position portion of the complete time code mssage.

4. A digital clock system as claimed in claim 1 wherein said logic means includes a random access memory.

5. A digital clock system as claimed in claim 1 wherein said logic means includes a firmware programmed micro-computer.

6. A digital clock system as claimed in claim 1 wherein the transmitted data is transmitted by a satellite orbiting the earth.

7. In a digital clock system in which a data is transmitted at a precise data rate, the data stream comprising a pluraity of contiguous data records, each data record comprising a plurality of data blocks, each of said blocks having a data synchronization segment and a message code segment, the message code segments within a data record forming a time code message and said message including a message synchronization portion and a time-of-year portion, a method of maintaining and correcting a time reference comprising the steps of:

receiving the transmitted data stream;

generating clock pulses at regular intervals;

phase locking said clock pulses to the precise data rate of said data stream;

detecting the data synchronization segment of a data block so as to determine the position of each following message code segment in the received data stream;

detecting the message synchronization portion of the time code message so as to determine the beginning of the time code message;

assembling the complete time code message from the individual received message code segments;

counting said clock pulses to provide a time reference;

comparing each complete time code message with the time reference represented by said counted clock pulses so as to provide a determination of whether said time reference coincides with the complete time code message; and

,

correcting the time reference represented by said counted clock pulses so that the time reference coincides with the complete time code message, responsive to a predetermined number of determinations of non-coincidence between said time reference and said complete time code message.

8. The method as claimed in claim 7 wherein the method further comprises the step of displaying the time represented by said counted clock pulses.

9. The method as claimed in claim 7 wherein the time code message further includes a satellite position portion, and the method further comprises the step of displaying the satellite position portion of the complete time code message.

10. The method as claimed in claim 7 further including the step of transmitting the data stream from a satellite orbiting the earth.