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Vol. 35, No. 8 March 23, 2011

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70 oPInIon

by John lowe

The author is manager of National 

Institute of Standards and Technology 

radio stations WWV/WWVH/WWVB.

While radio station WWVB may 

be familiar to readers of this publication, most people would not recognize 

those call letters. However, if you say 

you have an “atomic clock” hanging on 

the wall of your house, most everyone 

would know what you meant. 

Of course it is not a real atomic 

clock, but a radio-controlled device that 

receives the WWVB signal and corrects 

itself nightly when the 60 kHz signal 

propagates the best. 

In July 1956 the National Bureau of 

Standards started radio station KK2XEI 

in Boulder, Colo. It was a 2 kW transmitter sending a 60 kHz signal into the 

summer sky. Even though the effective 

radiated power was less than 2 watts, 

the signal was received and monitored 

at Harvard University in Massachusetts. 

This experiment showed that the frequency error due to the Doppler shift 

induced by the ionosphere was small. 

This was the forerunner of the WWVB 

broadcast. 

In April 1960 another experiment 

was conducted in the foothills of the 

mountains west of Boulder. A valleyspan antenna 3,400 feet long was strung 

near the old mining town of Sunset. The 

signal was broadcast with less than 15 

watts of power, yet it was consistently 

observed in New Zealand. 

Results from the Sunset experiment 

provided a much better understanding 

of the ionosphere and the study of 

whistlers, hiss, the dawn chorus and 

“sferics.”

This set the stage for the WWVB 

radio station. 

tIme’s tOP hAt

Construction began in 1962 on a site 

north of Fort Collins, Colo., near the 

small town of Wellington. The 390-

acre site was chosen in part for its high 

ground conductivity, a result of the high 

alkalinity of the soil. 

On July 5, 1963, WWVB began broadcasting a 7 kW signal at 60 kHz. In August 

of that year, its sister station, WWVL, 

began broadcasting a 500 W signal at 20 

kHz. On July 1, 1965, WWVB added a 

time code to the broadcast. 

The binary-coded decimal (BCD) 

time code transmitted 1 bit per second 

by shifting the power of the carrier by 

10 dB. The format is explained in the 

accompanying graphic on page 69. 

Over the next few years, improvements were made to increase the power 

up to approximately 13 kW, and it 

remained there until the late 1990s. In 

1972, the WWVL broadcast was terminated and its antenna became the rarely 

used WWVB backup antenna. 

Each antenna is a top-loaded dipole 

consisting of four 122-meter (400-foot) 

towers arranged in a diamond shape. 

Suspended between the four towers is 

a system of aluminum cables called a 

capacitance hat or “top hat.” The top 

hat is electrically isolated from the towers, but connected to a down-lead at the 

center of the diamond. The down-lead is 

the radiating element emanating from a 

helix house at ground level and also at 

the center of the diamond. 

The wavelength of a 60 kHz signal is 

nearly 5,000 m (more than 3 miles), so 

the length of the radiating element plus 

the top hat is much less than a quarter 

wavelength. Therefore, the top hat is 

inherently capacitive and a large inductor is added in the helix house to cancel 

the capacitance of the short antenna. A 

variometer, or variable inductor, is also 

included in the helix house to tune the 

antenna, which is especially useful during wind and ice loading. 

In 1997, work began to improve 

the WWVB broadcast. More powerful 

transmitters (FRT-72) were acquired 

from U.S. Navy surplus in Virginia, 

Scotland and Iceland. Extended tuning 

variometers were acquired from the 

decommissioned Navy low-frequency 

station NSS in Annapolis, Md. 

The WWVB broadcast was kept on 

the air during these upgrades by use 

of the old WWVL antenna. When the 

upgrades were complete on the WWVB 

side, the WWVL side was upgraded and 

they were combined with WWVB into 

a dual broadcast system. Broadcasting 

from both antennas, the WWVB signal 

was boosted to 50 kW of effective radiated power beginning in 1999. 

This increase in power created an 

explosion of new commercial radiocontrolled products, more than a million 

of which are sold each year. 

AnOtheR stAtIOn?

Despite the overall quality and reliability of these products, there are times 

and locations at which the WWVB 

signal is not well received or decoded 

properly. 

This is due to distance from the 

transmitter and also interference (added 

noise) to the signal caused by nearby radiating sources such as computer 

monitors or power transformers. To 

We Help Move Time Through the Air

Managers of WWVB Explore Options to Improve the Service Further

◗commentary

An idea being actively investigated is to add 

phase modulation to the existing WWVB signal while 

leaving the aM BCd code intact.

(continued on page 69)

The antenna towers of WWVB in Fort Collins, Colo.
69

RadioWoRld March 23, 2011 AdveRtIseR Index This listing is provided for the convenience of our readers. 

Radio World assumes no liability for inaccuracy. oPinion

page advertiser web site/url

56 acoustics First Corp www.acousticsfirst.com

43 aeQ, Sa www.aeqbroadcast.com

50 aM Ground Systems Co. www.amgroundsystems.com

12 armstrong transmitter Co. www.armstrongtx.com

62 audio technica www.audio-technica.com

5 audioScience Inc. www.audioscience.com

57 axia - a telos Company www.axiaaudio.com

63 Besco Internacional www.besco-int.com

63 Bext, Inc www.bext.com

48, 49 Broadcast depot www.broadcastdepot.com

41 Broadcast electronics www.bdcast.com

59 Broadcast tools, Inc www.broadcasttools.com

15 Broadcasters General Store www.bgs.cc

71 BSI www.bsiusa.com

3 BSW www.bswusa.com

10 Burk technology www.burk.com

63 Coaxial dynamics www.coaxial.com

7 Comrex Corporation www.comrex.com

16 Continental electronics Corp. www.contelec.com

40 Cordell Communications www.aarlon.com

52 davicom, a div. of Comlab www.davicom.com

19 daWnco www.dawnco.com

21 digigram www.digigram.com

8 digital alert Systems www.digitalalertsystems.com

63 digital radio engineering www.digitalradioengineering.com

4 erI www.eriinc.com

24 eSe www.ese-web.com

63 FM Services www.towermonitor.com

42 Gorman redlich Mfg www.gorman-redlich.com

58 Grace Broadcast Sales www.gracebroadcast.com

29, 53 Harris Corporation www.broadcast.harris.com

6 Heil Sound, Ltd. www.heilsound.com

20 Henry engineering www.henryeng.com

11 Inovonics Inc www.inovon.com

63 Intrinsicnet www.thestudiohawk.com

28 Isotrope LLC www.rfsigns.com

25 JK audio www.jkaudio.com

14 Kintronic Labs Inc www.kintronic.com

17 Logitek www.logitekaudio.com

33 Moseley associates www.moseleysb.com

47 Myat Inc. www.myat.com

23 nautel Ltd. www.nautel.com

30 nPr Satellite Services www.nprss.org

60 oMB america www.omb.com

13, 45 omnia - a telos Company www.omniaaudio.com

51 omnirax www.omnirax.com

61 oMt technologies/iMediatouch www.omt.net

35 rCS www.rcsworks.com

31 Sage alerting Systems www.sagealertingsystems.com

54 Shively Labs www.shively.com

32 Superior electric www.superiorelectric.com

9, 39 telos Systems - tLS Corp. www.telos-systems.com

34 thum & Mahr Gmbh www.yellowtec.com

1 tieline technology www.tieline.com

2, 36, 37, 72 Wheatstone Corporation www.wheatstone.com

27 Wide orbit www.wideorbit.com

help improve this situation, the transmitted power was increased about five 

years ago to 70 kW and the modulation 

depth was increased from 10 dB to 17 

dB. This helped, but has not solved the 

inherent problem of a poor signal-tonoise ratio at the receiver in the far field. 

New approaches were needed. 

The most obvious solution was to build 

another time signal station on the East 

Coast that operated at a different frequency. 

Several sites have been investigated including Greenbury Point in 

Annapolis; the Voice of America site 

in Greenville, N.C.; and some of the 

retired Loran-C sites. Funding for this 

opportunity was made possible with the 

American Recovery and Reinvestment 

Act. The stimulus money was allocated 

for a station to be built at the Redstone 

Arsenal in Huntsville, Ala. 

After much negotiation and investigation, NASA determined that they did 

not want a large low-frequency station 

so close to the Marshall Space Flight 

Center, also located on the arsenal. 

NASA was concerned that such a large 

amount of radiated power would interfere with their operations. 

Unfortunately, after all of these negotiations, time had run out for spending 

the ARRA money, so the funds had to 

be returned; now we are back to looking 

for other ways to improve our service. 

uPgRAde IdeAs

A possibility now being investigated 

is to upgrade the existing WWVB site 

further, by either building an antenna for 

a new broadcast frequency or splitting 

the antennas into two separate entities, 

as was done in the days of WWVL. 

The effect of broadcasting on two 

frequencies from the same location 

improves the chances of receiving at 

least one of the signals because the 

transmission nulls are related to frequency and therefore should occur in 

different locations. Also, interference 

may be affecting only one frequency at 

a given location. A receiver would need 

to determine which signal is strongest or 

more readable. This is already the case 

for radio-controlled devices in Japan 

receiving signals from radio station JJY 

on either 40 kHz or 60 kHz. 

Another idea being actively investigated is to add phase modulation to the 

existing WWVB signal while leaving 

the AM BCD code intact. This would 

allow all existing devices to continue 

to work, but allow a new generation 

of radio-controlled clocks to be developed. These new devices would have 

greater processing gain and therefore be 

capable of reading the time code with a 

lower signal-to-noise ratio.

These kinds of systematic, continuous improvement initiatives support the 

NIST goal of providing a reliable time 

source that can be received everywhere 

in the continental United States (and 

hopefully including Alaska and Hawaii). 

We envision that this will continue 

to go beyond clocks and watches and 

will become ubiquitous in consumer 

appliances. DVD players or microwave 

ovens will no longer blink 12:00 after 

a power outage. It will no longer be 

necessary to adjust any clocks when a 

Daylight Saving Time change occurs. 

Soon, accurate time will be displayed 

everywhere and we will have lost one 

more excuse for being late.

I invite and encourage readers to participate in a survey to help improve our 

services and to suggest new ones, at http://

tf.nist.gov/survey. You can learn more 

about the Time and Frequency Division 

of NIST at www.nist.gov/pml/div688/.

WWVB

(continued from page 70)

WWVB Time Code Format