Changes in the WWVB Radio Signal Affects Precision Frequency and Timing Reference
Spectracom had used the WWVB signal to synchronize its time and frequency references and master clocks in North America before the wide-spread use of GPS for precision timing applications. The last of these WWVB products has not been promoted for over 10 years and officially went end-of-life in 2005. A change in the WWVB signal was being considered in recent years to reduce impact of electro-magnetic interference and allowing for improved reception in consumer-grade clocks and watches1. However, this change affects the operation of precise time and frequency standards whose receivers are based on phase-locked loops, such as Spectracom WWVB receivers, so these products will no longer operate as intended.
 J.P. Lowe, “We Help Move Time through the Air”, Radio World, March 23, 2011, Vol. 35, No. 8 pp. 69, 70.