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
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
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. All copyrights (if any) are hereby acknowledged.
Note: I wrote a short
a couple years ago.
See all available
vintage QST articles.
WWV Moves to Colorado In Two Parts: - Part I
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 monopole antennas.
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.
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
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
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.
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.
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.
With 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
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 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.
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 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.
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
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.
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.)
* Chief, Radio
Standards Physics Division, National Bureau of Standards, Boulder, Colorado
1 QST, November,
1966, page 53.
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.