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.
of Contents]These articles are scanned and OCRed from old editions of the
ARRL's QST magazine. Here is a list of the
QST articles I have already posted. As time permits, I will
be glad to scan articles for you. All copyrights (if any) are hereby acknowledged.
Note: I wrote
a short story on WWVB a couple
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
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 monopole
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 transmitters.
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
The new 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 site.
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
The transmitter 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.
The 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.
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 without switching.
Hugh Stewart, Information Officer, views the base of one of the broad-band monopole standby
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.
As stated 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
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.
The bulk 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 Tam KH6EM.
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.
II, describing the frequency-controlling equipment, will appear in a subsequent issue.)
* Chief, Radio Standards Physics Division, National Bureau of Standards, Boulder, Colorado
1 QST, November, 1966, page 53.
2 This antenna was described in detail in November
1966 QST (Pappenfus, "The Conical Monopole Antenna"). -Editor.
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.