The National Institute of Standards and Technology (NIST) operates radio station WWVB which broadcasts the official time of the United States. WWVB is a 60 kHz standard frequency broadcast emanating from Ft. Collins, Colorado since 1965. The broadcast transmits the year, day, hour, minute, second and other time information using a one minute long amplitude modulated (AM) format. This time code broadcast has created a commercial industry of radio-receive clocks (RCC) and watches that number over a million sales per year. However, the reception and decoding of the AM code is limited by low power at long distances away and by interference from external frequency sources. Therefore, NIST has implemented a new phase modulation (PM) scheme for the WWVB broadcast that retains the legacy AM format but will allow new PM capable receivers to decode the time information with greater gain and effectiveness. This chapter describes the new PM format.
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