New Signals Trom an Old Timer

’i1New Signals trom an Old Timer

181 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 de 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 other 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 of aligning the beginning of 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 of once 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 ENGINEERING wwv

Fig. 2 The WWV (topside) and WWVH (bottom) format wheel, showing information transmitted each minute of the THE 29th SECOND PULSE OMITTED.. . . BEGINNING OF EACH MINUTE IDENTIFIED FORMAT 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 recorder and can be easily read by eye with a little practice. Another new feature of the broadcast is provision for 45-second announcements 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

July, 1971 80 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-- .icy diversity receiver should thus

20 vide the reliability needed for re-

W broadcast purposes. Such receivers 0 3 are available commercially from at 50 + least one company specializing in 24 WWV receivers. -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 -80, geographical coverage on its various LONGITUDE frequencies in the Western Hemi- 80 sphere, some maps giving best usable frequencies are provided. 60 These plots are the result of com- puterized calculations of coverage 40 predictions made by NBS before relocating WWV from Greenbelt, 20 Maryland to Fort Collins, Colorado

W in 1966. They take into account n 2 seasonal and day-to-night variations to and also variations due to the 11- c 4J 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 -80 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 clock to insure that the Fort Collins December nighttime. Map B is for December daytime. 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 of a 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 of 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 of the announced time. not generally the case on a given WWV keeps right on ticking away.

44 BROADCAST ENGINEERING