![]() The data content, physical properties and scheduling features of this BPSK time code may be found here:Įnhanced WWVB Broadcast Format (revised ) ![]() The phase-modulated information may take several different forms, with the basic one having a frame duration of one minute, as in the legacy AM/PWM broadcast. This time code, also operating at a rate of 1 bit/sec, is delayed by 0.1 s with respect to the first time code described above, such that 180-degree transitions in the carrier phase can only occur 0.1 s after the 17 dB power reduction that is created by the pulse-width-modulation. In the PM format, binary-phase-shift-keying (BPSK) modulation is used, wherein the carrier's phase is unaffected when conveying a "0" and is inverted (i.e. Existing radio-controlled clocks and watches are not affected by this enhancement and continue to work as before. This enhancement to the broadcast provides significantly improved performance in new products that are designed to receive it. Since October 29, 2012, NIST Radio Station WWVB has been broadcasting a phase modulated (PM) time code that has been added to the legacy AM/pulse-width-modulation signal. The pulse-width modulated time code contains the year, day of year, hour, minute, UT1 time correction and flags that indicate the status of Daylight Saving Time, leap years, and leap seconds, as listed in the legacy WWVB time code format description and detailed in NIST Special Publication 432 (NIST Time and Frequency Services). In the first of the two formats, based on PWM, which has been in use for several decades, the carrier power is reduced by 17 dB at the start of each second and restored to full power 0.2 s later for a binary "0", 0.5 s later for a binary "1", or 0.8 s later to convey a position marker. The time codes are synchronized with the 60 kHz carrier and are broadcast continuously in two different formats at a rate of 1 bit per second using pulse width modulation (PWM) as well as phase modulation (PM). WWVB continuously broadcasts digital time codes on a 60 kHz carrier that may serve as a stable frequency reference traceable to the national standard at NIST. In addition, WWVB may be used in other consumer timekeeping applications, such as appliances, cameras, and irrigation controllers, as well as in high level applications such as accurate time synchronization. ![]() The WWVB broadcasts are used by millions of people throughout North America to synchronize consumer electronic products like wall clocks, clock radios and wristwatches. NIST radio station WWVB is located on the same site as NIST HF radio station WWV near Fort Collins, Colorado.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |