History of WWVB
WWVB began operation as radio station KK2XEI in July 1956. This experimental station was operated from 1530 to 2000 hours universal time each working day from Boulder, Colorado. The continuous wave 60 kHz signal was not modulated, except for a call sign ID that was sent every 20 minutes. The effective radiated power (ERP) was originally said to be 40 W, but later reduced to 1.4 W. Data recorded in January 1957 showed that the frequency of the broadcast was within a few parts in 1010 of the national standard located in the adjacent Boulder laboratory, proving (as expected) that a LF transmission was far more stable than the signals from WWV and WWVH.
The success of the 60 kHz broadcast led to the construction of a very low frequency (VLF) radio station named WWVL, which began operation from Sunset, Colorado in April 1960 using a carrier frequency of 20 kHz. It was originally planned to use the 20 kHz for worldwide coverage, and the 60 kHz broadcast for coverage of the United States. In March 1960, the call sign WWVB was obtained by NBS for the 60 kHz station. The “B” in the call sign probably stands for Boulder, the site of the original transmitter. However, one interesting theory is that the “B” could stand for Brown. W. W. Brown, one of the designers of the Fort Collins station, was employed as a contractor by NBS when the call sign application was submitted. Perhaps not coincidentally, his initials were W. W. B.
In 1962, NBS began building a new facility on a site north of Fort Collins, Colorado that would later also become the home of WWV. The site was attractive for several reasons, one being its exceptionally high ground conductivity, which was due to the high alkalinity of the soil. It was also reasonably close to Boulder (about 80 km, 49.3 mi), which made it easy to staff and manage, but much farther away from the mountains. The increased distance from the mountains made it a better choice for broadcasting an omni-directional signal.
WWVB went on the air on July 5, 1963, broadcasting a 5 kW signal on 60 kHz. This was later increased to 7 kW and then 13 kW, where it remained until December 1997. WWVL began transmitting a 500 W signal (later increased to 2 kW) on 20 kHz the following month. WWVL had a relatively short life span, going off the air in July 1972, but WWVB went on to become a permanent part of the nation’s infrastructure.
A time code was added to WWVB on July 1, 1965. This made it possible for radio clocks to be designed that could decode the signal, recover the time, and automatically set themselves. The time code format has changed only slightly since 1965; it uses a scheme known as binary coded decimal (BCD), which uses four binary digits (bits) to send one decimal number.
The WWVB broadcast continued operations up to the 1990’s with only minor modification to the format or equipment. The number of customers was relatively small, mostly calibration laboratories who operated WWVB disciplined oscillators, devices that utilized the 60 kHz carrier as a frequency reference. Also, the limitations of the aging transmitting equipment at WWVB became increasingly apparent as the years passed. The situation came to a head on February 7, 1994 when a heavy mist froze to the antenna, and the antenna tuning system could not compensate, shutting down the WWVB broadcasts for about 30 hours. After reviewing the available options, it was decided that a redesign of the entire WWVB transmitting system was necessary.
During the discussions about redesigning WWVB, it was decided to substantially raise the power level of the broadcasts. It was obvious that WWVB could play a much larger role and reach far more customers if the signal were easier to receive. In Europe, low cost radio controlled clocks were beginning to appear, designed to synchronize to stations such as MSF in the United Kingdom and DCF77 in Germany. These stations were very similar to WWVB, but had a much smaller coverage area to service. As a result, European customers were able to purchase radio controlled alarm clocks, wall clocks, and wristwatches at reasonable prices. These products lacked the external antennas and high sensitivity of the laboratory receivers, but would undoubtedly work well in the United States if the WWVB signals were made stronger.
Expert consultants and engineers from the U.S. Navy’s LF/VLF support group were hired by NIST beginning in October 1994 to evaluate the WWVB system and propose changes. Their reports suggested that although the antennas themselves were in reasonably good shape, the transmitters and matching equipment should be completely redesigned and new or upgraded equipment installed. The project progressed in phases over the next several years, as funding and equipment became available. Discussions between agencies at the highest levels resulted in the transfer of modern LF transmitters and other equipment from recently decommissioned Navy facilities to NIST. New station staff members were hired who had previous experience with the new systems and equipment. Contractors normally employed by the Navy for LF work were hired to design a new broadcast control system fully utilizing the assets of the existing station.
A formal announcement that the WWVB power was to be increased was made during 1996, and a significant number of low cost radio controlled clock products were introduced in the United States shortly after the announcement. By December 1997, an interim stage of the upgrade was completed and the ERP was increased to about 25 kW. By August 5, 1999, the upgrade was complete. The new WWVB configuration used two modern transmitters operating into two antennas that simultaneously broadcast the same 60 kHz signal. This increased the ERP to 50 kW, about four times more power than the pre-upgrade configuration . This power level was later increased to its current level of about 70 kW. The increase in power greatly increased the coverage area, and low cost radio controlled clocks that synchronized to WWVB soon became commonplace throughout the United States.
Questions? Send mail to: Michael Lombardi