is the first of a two-part series on the move of the WWV transmitter
stations operated by the National Bureau of Standards (now called
National Institute of Standards and Technology) from Greenbelt,
Maryland, to Boulder, Colorado.
WWV Part II appeared in the February 1967 edition of the ARRL's
QST magazine. WWV began transmitting time / frequency standards
in 1920 in order to provide a means for remote stations and laboratories
to calibrate local standards that would prevent transmitting stations
from interfering with each other. Although most people don't realize
it, the 60 kHz signal that their 'atomic' clocks and watches
use to self-adjust time emanates from the WWVB antenna in Boulder.
This first installment of the article discusses the history and
rationale for relocating the WWV facility to a new location. The
second part gets into the technical aspects of the WWV facility's
equipment and operation. As usual, I am amazed at the pioneers who
conceived of, designed, and implemented these kinds of operations.
January 1967 QST
Wax nostalgic about and learn from the history of early electronics. See articles
QST, published December 1915 - present. All copyrights hereby acknowledged.
Note: I wrote a short story on
WWVB a couple years ago.
WWV Moves to Colorado
In Two Parts: - Part I
By Yardley Beers, W0EXS
At 0000 GMT on December 1, 1966, the veteran standard time and frequency
station WWV at Greenbelt, Maryland, closed down forever, and at
essentially the same instant a new station with the same call letters
and services came on the air from Fort Collins, Colorado. The event
was commemorated for amateurs and short-wave listeners by the availability
of a special QSL for those who reported hearing the new station
in its first hours of operation, as announced earlier.1
Peter Viezbicke W0NXB, chief engineer for design and construction
of the new station (left), and Leo Honea W A3ADB, ex-KH6MG,
engineer-in-charge of WWV, stand in doorway of new transmitter
building. The inscription "WWV" in the background was brought
from the Greenbelt building to Fort Collins.
Artist's rendition of WWV building and the eight antenna masts
which form an arc an the ridge east of the building. To the
left is the 200·ft. high 2.5-MHz. dipole antenna and to the
right the 100·ft. high 5.0-MHz. dipole. Between them are the
dipoles for the 2.5-, 10.0-, 15.0-, and 20-MHz. signals. In
the left and right foreground are the two 88·foot standby wide-band
A view of the 20- and 2.5-MHz dipole antennas.
One of the monopole standby antennas and one of the dipole single-bond
antennas. The striped tower in the background is one of the
four supporting the WWVL main antenna. The building is the WWVB-WWVL
Transmitter Building before the addition of the new wing.
There were several reasons for the construction of the new
station and for the move. In the first place, the old station was
obsolescent, and maintenance was a serious problem. The difficulty
of maintenance was aggravated because the station, in addition to
providing a continuous service, had always had some experimental
aspects to its program, and there had been frequent innovations
and modifications to the equipment. Unfortunately, inadequate records
of cable connections had been kept, and long ago the staff members
who made them departed for retirement or for other employment. Nowadays
good record are being kept so that this particular difficulty should
not return. At any rate, for many years the station was kept on
the air with a remarkable degree of continuity through the conscientiousness
and ingenuity of the staff in the presence of serious obstacles.
In contrast, the new station, employing the latest transmitter
designs, provides much more efficient operation. In addition, there
is much greater flexibility, since the transmitters are comprised
of identical units - except that some of the transmitters, being
higher powered than the others, contain one more amplifier stage
which can be tuned to any frequency. In the old station only a
few of the eight transmitters were identical. Unlike the old transmitters,
in the new ones modulation is applied at low levels, and all subsequent
stages are accurately linear. In this way there is available a wide
choice of modulation types: a.m. or single sideband, with either
sideband, and with any arbitrary degree of carrier suppression that
may be desired. Thus, the new transmitters contain the same design
features which are generally considered desirable modern amateur
The wide flexibility of modulation is particularly
advantageous with respect to coordination with WWVH in Hawaii, which
uses the same carrier frequencies. This station, also obsolescent,
is expected to be rebuilt a few years hence. In this event, similar
features will be incorporated. Then the upper sideband can be used
by one station and the lower by the other, and users who wish to
distinguish between the two stations will be able to do so much
easier than at present.
A survey made by the organization
which was then known as the Central Radio Propagation Laboratory
of NBS (now the Institute for Telecommunication Sciences and Aeronomy
of ESSA) in Boulder indicated that the signal strength coverage
would be better or just as good from the new site - except, of course,
for the small area in the vicinity of Washington, D. C., which has
been served by ground-wave propagation. The area which should be
aided notably by the relocation will be the West Coast of the U.
S. A. Here the propagation time delays of signals from WWV and WWVH
were nearly equal, and it was difficult to separate the time pulses.
Also, reception frequently was marred by fading, resulting from
the fact that the signal strengths were usually nearly equal. With
the relocation, this region is pushed out into the Pacific Ocean,
where there are few users.
Finally, there is the advantage
of administrative efficiency. WWV is now located on the same site
as two other NBS standard-frequency and time stations, WWVB (60
kHz.) and WWVL (20 kHz.). Therefore, there can be some reduction
in staff since all of the transmitters can be monitored from a single
point, and the staff of one station can assist or fill in at the
other in case of emergency. Furthermore, communication lines with
the parent organization responsible for the administration of these
stations, the Radio Standards Laboratory of the National Bureau
of Standards in Boulder, Colorado, are greatly simplified. Also,
it is easier to synchronize the station with the NBS Atomic Standards,
which are located in Boulder.
When the Greenbelt station
was established, the property was under the jurisdiction of the
U. S. Department of Agriculture. The radiation of standard-frequency
signals did not disturb agricultural experiments that were conducted
in adjacent fields. However, in time, jurisdiction passed to NASA,
who constructed the laboratories of the Goddard Space Center adjacent
to the transmitter site. When NASA was confronted with the problem
of trying to conduct experiments under conditions where a few inches
of unshielded wire would give a sizeable deflection on an oscilloscope,
their management requested that when NBS replaced its obsolete transmitters
they be relocated at some more remote point. This situation also
encouraged the move to Fort Collins.
Before the final decision
to rebuild and relocate WWV was made, permission was obtained to
allow a special voice announcement to be made over it for one month
in the summer of 1964. In it, listeners were requested to write
in. The some 4,600 who did were sent a rather lengthy questionnaire,
and about 3,500 of these were returned filled out. About one-quarter
of the respondents were representatives of organizations. These
statements in themselves indicate the need for the station. It is
interesting to note that 35 percent of the respondents were licensed
radio amateurs, confirming the interest of amateurs in the station.
The detailed answers provided guidance in determining which of the
services should be retained and which should be changed and how.
They also provided assurance that the specific needs of the Washington
ground-wave high-accuracy area would be met largely by other existing
services. It might be noted that 10 MHz. was the most widely used
carrier frequency and 25 MHz. was the least.
Layout of the Fort Collins Site
site is located about seven miles north of the City of Fort Collins
on Colorado Route No.1, and is about an equal distance to the east
of the first foothills of the Rocky Mountains. The land is nearly
flat. The soil has a high alkali content and a high electrical conductivity.
Portions of three small lakes are contained within the area of the
The most conspicuous feature is the group of nine
400-foot towers which supports the WWVB-WWVL main and standby antennas.
The building housing those transmitters is amongst these towers.
These antennas are essentially top-loaded verticals with arrays
of horizontal wires forming capacitive hats and with the bottom
ends of the vertical radiators terminating in "helix houses" (actually
two stories tall) containing loading coils. The ground conductivity
has been improved by burying a network of wires.
If there were Nielsen ratings for the non-broadcast services,
WWV would no doubt top the list - perennially. Now, after forty
years in the Washington, D. C., area, the station has been moved
to the West. Here is an overall description of the new facilities
at Fort Collins, Colo.
The new WWV station was financed by a Congressional appropriation
of $970,000. The largest expenditure has been for the transmitters.
However, a considerable portion has been used in constructing the
new building and in adding a new wing to the old building. The new
building is one story high and is located in a depression in the
terrain so that its roof is approximately level with the ground
of the area to the north, where the WWV antennas are located. Thus,
the building should cause no shadows in the antenna patterns. In
the main portion of the new building, there are located eight transmitters
along an area adjacent to three of the outside walls. The area adjacent
to the fourth outside wall, the front, contains the main entrance
and offices. The center of the building contains a laboratory and
shielded enclosures for housing the frequency-control equipment.
Wings of the building contain a workshop, a garage, and a diesel-powered
generator for emergency power. Commercial electric power is supplied
by underground cables from two different sources. The building is
thoroughly air-conditioned, since dust was a major maintenance problem
at the old station at Greenbelt, and it is recognized that potentially
the problem is likely to be worse at the new location on open prairie.
The addition to the old building contains some offices for
administration of the whole site and such much-needed amenities
as a conference room and a small kitchen. The road system is such
that visitors come first to the old building, and hence these central
facilities are located here.
Incidentally, visitors who
make advance arrangements through either the Boulder or Fort Collins
offices are most welcome. In such cases we can be sure to have someone
on hand to receive them. However, unannounced visitors are to be
discouraged, as the staff is small and often there is no one who
can leave his duties to receive them.
The WWV Antenna System
Table 1 - Locations of WWV Antennas
power levels are slightly increased, but the transmission frequencies
at the new station are the same as at the old: 2.5 kw. on 2.5, 20,
and 25 MHz., and 10 kw. on 5, 10, and 15 MHz. At both the old and
new stations it was considered necessary to have eight transmitters:
six in operation and two as standby.
In the old WWV there
was a schedule for the rotation of transmitters so that in turn
each transmitter was taken out of action for a while for cleaning
and other maintenance, the switchover taking place during one of
the scheduled silent periods so that the transmission schedule was
uninterrupted. Also, at the old WWV the antennas were fed by open-wire
lines which were switched between transmitters. However, at the
new WWV in Fort Collins, antennas are fed by rigid coaxial line,
and each one is connected permanently to a single transmitter, the
layout being such that no two coaxial lines cross. Altogether there
are eight antennas at the site. Six are half-wave modified "sleeve"
vertical dipoles, one for each of the above frequencies. The remaining
two are broadband h.f. monopole antennas for the two standby transmitters.
These eight are located approximately at equal intervals on a semicircle,
with the two wide-band standby antennas at the opposite ends of
the semicircle, and the others placed in such a way to make interaction
a minimum, The exact locations are given in Table I.
half-wave vertical antennas, with heights compensated for end effects,
employ standard commercial tower sections and are designed to withstand
winds up to 112 m.p.h. The antennas are center-fed with rigid coaxial
cable and are mounted on hinged bases fastened to concrete foundations.
The upper one-quarter wavelength section, supported on insulators
from the lower one quarter wavelength section, constitutes the upper
half of the radiating system. The sleeve consists of nine equally-spaced
quarter-wave-long wires connected from the center of the tower (one-quarter
wavelength above ground) that slope downwards to the ground at an
angle of 45 degrees. This sloping skirt, each wire appropriately
insulated from ground, not only functions as the lower half of the
radiating system, but also serves to guy the antenna.
this design the driving point impedance is approximately equal to
the 50-ohm coaxial line, and the current developed at the junction
of the base and ground plane is minimized. This permits connecting
the coaxial shield and the tower base directly to ground. In addition,
tests made on the antenna indicated that a radial ground screen
did not make any detectable change in the input impedance; thus
it was not incorporated into the system.
This design, readily
adaptable to a coaxial feed line, provides low angle omnidirectional
radiation and yields a gain of approximately 1.7 db. over its one-quarter-wavelength
monopole counterpart. By employing a double-stub adjustable tuner,
it can be matched precisely to 50 ohms. Finally, with the shorted
stubs connected into the feed line at the antenna base, each is
at d.c. ground potential, thus protecting the transmitters from
possible lightning damage.
The wideband standby antennas,
also fed by 50-ohm rigid coaxial line, are series-excited, base-fed,
vertically-polarized, omnidirectional radiators. The antennas operate
over a radial ground screen and cover a frequency range of 2.5 to
25 MHz.2 The antennas are capable of handling 50 kw.
of power with a nominal standing wave ratio of less than 2.5 to
1 when connected to a 50-ohm line. Continuous coverage is accomplished
Hugh Stewart, Information Officer, views the base of one of
the broad-band monopole standby antennas.
The eight transmitters contain
bandswitching units which are identical except for the obvious difference
that four of them have high-powered amplifiers. Thus, although the
single-band antennas cannot be switched between transmitters in
case of breakdowns units may be interchanged.
earlier, modulation is introduced at very low levels, and s.s.b.
or a.m. may be used with any degree of carrier suppression which
may be desired. Provision is included even for applying different
modulations on the two sidebands, although there is no contemplation
of the use of this feature in the near future. The s.s.b. generator
uses a crystal filter at 5 MHz., and provision is made for synthesizing
all oscillator frequencies from the local cesium atomic standards.
A great deal of attention has been paid to obtaining frequencies
of high spectral purity.
The modulation is controlled by
an elaborate device called" the time code generator-programmer",
and two spares are on hand in case of breakdown. This device, in
conjunction with an announcing machine and two code keyers, provides
the complete WWV audio modulation program. Such features of the
program as propagation forecasts, geoalerts, and UT2 corrections3
are readily changed as necessary by manual switches on the announcing
machine or by replacing code wheels on the keyers.
of the transmitters is composed of linear amplifiers, which are
standard commercial stock items, identical with some which are in
wide use by military, commercial, and amateur stations. However,
because of the severe requirements for reliability with twenty-four
hour daily operation, the power amplifiers are derated to fifty
percent of their normal levels: for example, the amplifiers which
are used at 10 kw. output are ones which in standard commercial
service would be rated at 20 kw. (Such derating had also been in
practice at the old station.) The building layout is such that the
power of each transmitter can be raised from its present level by
the addition of at least one more stage, should it be desired at
a later time.
Participation of Amateurs
The engineers in charge of all three stations are amateurs:
Leo Honea WA3ADB, ex-KH6MG (WWV); Richard F. Carle K0LYM (WVVB-WWVL);
and Sadami Katahara KH6DK (WWVH). Also, the engineer in charge of
the design and construction of the new WWV is an amateur: Peter
P. Viezbicke W0NXB. Other amateurs on the staff of the stations
are John A. Duffield K0KHZ, Howard E. Michel, Jr. K0BPY, and George
Amateurs participating in other parts of the
NBS Time and Frequency Program include: Miss Kay Barclay K0BTV,
Don Halford W0JVD, Don Hilliard W0EYE, Edward Rogers K0GKB, J. E.
Gray, W0GNV, and the author.
(Part II, describing the frequency-controlling
equipment, will appear in a subsequent issue.)
Radio Standards Physics Division, National Bureau of Standards,
Boulder, Colorado 80302.
QST, November, 1966, page 53.
2 This antenna was described
in detail in November 1966 QST (Pappenfus, "The Conical Monopole
3 Information on these services is contained
in NBS Miscellaneous Publication 236, ". BS Standard Frequency and
Time Services," 1966 edition; for sale by the Superintendent of
Documents. U. S. Government Printing Office, Washington, D. C. 20102,
price 15 cents.