’i New Signals
1 8 1 wwv Fig. 1 On occasion, operator makes television time com-
By Lowell Fey’, WWV. Ft. Collins, Colo. parisons at NBS Boulder. Sandra Danielson of the Broad-
cast Services is at the controls.
Although many other changes arranged into new places with some tones every other minute (with some
have occurred in broadcasting over periods where 500 Hz is added for exceptions) or the 440 Hz tone once
the years, those who tune in to the good measure. All use of the Morse per hour may still be used. In ad-
National Bureau of Standards time Code will be dropped along with dition, the 45-second slots not used
broadcast stations WWV and the NASA 36-bit “buzz saw” code for announcements will be used for
WWVH have come to expect the which will be replaced with a one- a 500 Hz tone. NBS takes the point
same familiar time signals year bit per second IRIG H time code of view that some kind of modula-
after year. But not much longer. on a 100 Hz subcarrier. There still tion should be present nearly all the
Soon a new broadcast will be heard will be geoalerts and sorile othx time to make the signal easy to find
with more kinds of services than announcements. There no longer when tuning it in.
before for a wider variety of time will be any completely silent The new format is designed to
and frequency users. periods. serve a new class of users. These
Starting July 1, 1971 there will Now, let’s look at the new format users make slow-speed strip chart
be more frequent voice time an- from the user’s standpoint. The recordings and desired timing marks.
nouncements, a different way of casual clocksetter will never have At speeds of 1 ” per hour, marks
marking hours and minutes, no si- to wait longer than a minute to once per hour should serve. These
, lent period, and no more Morse get time-of-day information. This can be obtained from either of two
d e or the fast NASA time code. feature will also benefit those who sources. In a high signal-to-noise
instead, a slow time code will be wish to time tape recordings of area the 0.8 second 1500 Hz tick
added along with some o t h e r various occurrences; €or instance, can operate a frequency sensitive
changes. intermittently occurring conversa- circuit such as a resonant reed
In many respects the services will tions between a radio dispatcher and relay to provide a marker signal.
be the same. The WWV transmit- outlying stations. To time the oc- The same use could be made of
ters will remain at Fort Collins, currence of short exchanges, the the 440 Hz hour marker, but since
Colorado, broadcasting on the same tape recorder need run no more it lasts 45 seconds much better
frequencies of 2.5, 5 , 10, 15, 20, than one minute. For all these uses noise discrimination can be ob-
and 25 MHz. Power output will the tick at the beginning of the first tained. Absence of this signal at
not change from the present 10 kW second will be lengthened to 0.8 2400 hours can be used to mark
on 5, 10, 15, and 20 MHz and second to provide easier recogni- the beginning of the Greenwich
2.5 kW on the other frequencies. tion of the beginning of the minute. mean time 24-hour day. For faster
The ticks will continue nearly as For more precise clock setting, strip chart recordings the same
before: 5 cycles of 1000 Hz each the well-known oscilloscope tech- technique can be used to mark each
second, There will be a special tick nique o aligning the beginning of
f minute with the 0.8 second 1000
0.8 seconds long to mark the be- a received 5 ms 1000 Hz tick with Hz tone, or every other minute with
ginning of each minute. This tick the scope trigger from a local clock the 600 Hz tone.
will also be 1000 Hz except €or may still be used. No matter what If complete identification of the
the first one each hour, which will other modulation is on the station time of Occurrence of a recorded
be 1500 Hz. at the time, the 5 ms tick will al- event is required, this also may be
Voice announcements will be ways be protected from interference obtained using the IRIG H code.
once each minute instead o once
f from this modulation by being ap- This code has a bit rate of once
every five minutes. But . . . aP- propriately located in a 40 ms per second and gives the day num-
parently nothing is safe from Wom- “hole” chopped in the modulation. ber of the year and the hour and
en’s Lib . . . time announcements Knowledge of propagation delay minute. This information is pre-
from WWV’s sister station, WWVH then makes time synchronization to sented in binary coded decimal
ir! Hawaii, will now appropriately about 1 ms possible, as before. form and is repeated each minute.
in a woman’s voice, even ending On the new WWV and WWVH
with a friendly Aloha! There will Standard Audio Tones format, the code will be amplitude
still be the same audio tones as For standard audio frequency modulated on a 100 Hz subcarrier,
before, 440 and 600 Hz, but re- comparison purposes the 600 Hz which may not be audible using an
44 BROADCAST E N G I N E E R I N G
Fig. 2 The WWV (topside) and WWVH
(bottom) format wheel, showing infor-
mation transmitted each minute of the THE 29th SECOND PULSE OMITTED....
BEGINNING OF EACH MINUTE IDENTIFIED
hour. BY 0.8 SECOND LONG 1200H2 TONE (TYPICAL)
ordinary receiver. With filtering and
clipping, however, it will be suitable
for recording on a strip chart re-
corder and can be easily read by
eye with a little practice.
Another new feature of the broad-
cast is provision for 45-second an-
nouncements every other minute
(again with some exceptions) from
her government agencies for their
in purposes. The geoalerts and
propagation forecasts presently
broadcast by WWV would fall into
this category. There is room for 24
WWV transmission frequency st an
arbitrary transmitter location. In the
60 continental U.S., however, at lea3
one of WWV’s frequencies should
40 always be receivable. A freqi--. c iy
diversity receiver should thus
vide the reliability needed for re-
broadcast purposes. Such receivers
3 are available commercially from at
+ least one company specializing in
-20 For general listening use, almost
any short wave receiver will suffice.
-40 However, there are a number of
special purpose timing receivers
-60 available capable of being fix-tuned
to any of WWV’s frequencies. For
those who are interested in WWV’s
geographical coverage on its various
LONGITUDE frequencies in the Western Hemi-
sphere, some maps giving best
usable frequencies are provided.
60 These plots are the result of com-
puterized calculations o coverage
40 predictions made by NBS before
relocating WWV from Greenbelt,
20 Maryland to Fort Collins, Colorado
in 1966. They take into account
2 seasonal and day-to-night variations
t o and also variations due to the 11-
year sunspot cycle. The peak of the
-20 sunspot cycle occurred in 1969.
So far, nothing has been 5
-40 about the source of WWV’s time.
This is, of course, the world-famous
-60 NBS atomic clock located in the
NBS research laboratories at
Boulder, Colorado. Fort Collins is
located 50 miles away and has its
LONGITUDE own clock system, so intercompari-
Fig. 4 Map A shows the frequencies (in MHz) around the Western Hemis- sons must be made with the Boulder
phere that are predicted to be the best for WWV time announcements for
December nighttime. Map B is for December daytime.
clock to insure that the Fort Collins
clock is kept in agreement. These
are made every day using the sig-
such announcements each hour on To allow this, the new on-the- nals from a Denver television sta-
WWV and 23 on WWVH. hour broadcast will say: “At the tion to relate the times of the two
tone (pause) 23 hours Greenwich clocks. The time of reception o a f
Commercial Use Mean Time.” (tone) (pause) “Na- specific “sync pulse” is noted at
Even with all these changes, one tional Bureau of Standards Time.” both Boulder and Fort Collins.
might never think of hearing WWV (pause) “This is radio station WWV, Knowing the television signal propa-
time signals coming from anywhere . . .” The part to be rebroadcast gation delay between the two loca-
but the WWV transmitters at Fort would be only the tone marking tions then permits a time compari-
Collins, Colorado. But, that also the beginning of the hour and the son accurate to a few billionths of
may change. The new time an- words “National Bureau of Stan- a second.
nouncements are arranged so that dards Time.” The local announcer While this is a much better ac-
WWV on-the-hour time signals can would identify the hour of the tone curacy than can actually be re-
be rebroadcast as a public service according to his own time zone. ceived on WWV, it insures that
by any commercial broadcast sta- In order to make sure the time the almost incredible accuracy o f
tion capable of tuning them in on announcement can be rebroadcast the atomic clock-about a part in
a receiver. The National Bureau of reliably, the WWV signals must be lO“-is available to prevent ar
Standards only requires that the re- continuously receivable at the com- long-term drifts or fluctuations fro
broadcast be direct and not delayed, mercial transmitter locations. Due occurring in the WWV clocks. That
and that NBS is identified as the to propagation variations, this is will also make sure that old timer
origin o the announced time.
f not generally the case on a given WWV keeps right on ticking away.
44 BROADCAST ENGINEERING