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Distribution of Standard Frequency and Time Signals

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Distribution of Standard Frequency and Time Signals Distribution of Standard Frequency and Time Signals Abstract-This paper reviews the present methods of distributing stan- tional frequency bands are given in Table 11. Many of these dard frequency and time signals (SFTS), which include the use of high-fre- stations participate in the international coordination of quency, low-frequency, and very-low-frequency radio signals, portable time and frequency and are identified in the tables. The clocks, satellites, and RF cables and Lines. The range of accuracies attained with most of these systems is included along with an indication of the sources signal emission times of the coordinatcd stations are within of error. Information is also included on the accuracy of signals generated by 1 millisecond of each other and within about 100 ms of frequency dividers and multipliers. UT2 ; their carrier frequencies are maintained as constant as Details regarding the techniques, the propagation media, and the equip possible with respect to atomic standards and at the offset ment used in the distribution systems described are not included. Also, the from nominal as announced each year by the Bureau Inter- generation of the signals is not discussed. national de I'Heure (BIH) [4]. The fractional frequency I. INTRODUCTION offset in 1966 was - 300 parts in IO'', and this value is to be used in 1967. HE DISTRIBUTION of standard frequency and The long and widespread experience with standard HF time signals (SFTS) with the highest accuracy over and time signals, and their present world-wide use, under- long distances has become increasingly important lines their importance to a large body of users. There are in many fields of science. It is essential for the tracking of international organizations, such as the International Radio space vehicles, worldwide clock synchronization and oscilla- Consultative Committee (CCIR) [SI, the BIH [4], and the tor rating, international comparisons of atomic frequency International Scientific Radio Union (URSI) [6],[7], that standards, radio navigational aids, astronomy, national are concerned with many aspects of their operation and standardizing laboratories, and some communication sys- utilization, such as reduction of mutual interference, broad- tems. Methods used include use of high-frequency (HF), cast accuracy, synchronized emission times, etc. For in- low-frequency (LF), and very-low-frequency (VLF) radio stance, the CCIR not only publishes information on signals transmissions, portable clocks, satellites carrying a clock or but also is engaged in a study program designed to improve a transponder, and RF cables and lines. the services and uses of the present stations. This paper will review these distribution systems and A technique employed by NBS to improve the transmitted some of their limitations and also indicate some promising accuracy of the frequencies of WWV' and WWVH was to techniques for future study. Recent advances [ 1 ] in the dis- use the received signals of WWVB (60 kHz) and WWVL (20 tribution of SFTS will be included, but they will not always kHz) at these stations to remotely control them [8]. The be specifically pointed out. Information will be included on NBS atomic standards are located at Boulder, Colo., and the accuracy of SFTS signals generated by frequency di- the transmissions of WWVL and WWVB, which stations viders and multipliers. Details regarding the techniques, are located about 50 miles away, are remotely phase- the propagation media, the equipment involved in the dis- controlled by means of a VHF phase-lock system [9] con- tribution systems described, and the generation of the nected between them and the atomic standard at Boulder so SFTS are not included. that their transmitted frequency accuracy is essentially that The definition of the terms stability, precision, and ac- of the NBS standard. Because of the high received frequency curacy as used in this paper are essentially the same as those accuracy of LF and VLF signals, it was thus possible to. given in another paper [2]. improve the frequency control of WWV and WWVH. 11. DISTRIBUTIONBY RADIO SIGNALS Later, the carrier frequencies and time signals of WWV and A. Distribution by HF and VHF Signals (3 to 300 MHz) WWVH were phase-locked to the received signals of WWVL and WWVB, so that they might be used to obtain At present there are about 15 standard HF and time- time (epoch) [42]. signal broadcasting stations [3], [4] operating in the allo- The received accuracy of the HF time interval and epoch cated bands between 2.5 and 25 MHz. Table I lists them signals depends on many factors, such as the averaging along with certain characteristics, such as location, carrier time, the length of the radio path from transmitter to re- frequencies and power, period of operation, carrier offset, ceiver, the condition of the ionosphere, whether the path is etc. The characteristics of the HF and VHF stations that partially in light and darkness or not, the frequency used, broadcast standard frequency and time signals [3] in addi- WWV was located at Beltsville, Md., until December 1, 1966, and is Manuscript received December 13, 1966; revised January 6, 1967. now at Ft. Collins, Colo. All references in this paper are to the Beltsville The author is with the National Bureau of Standards, Boulder, Colo. location. TABLE 1 CHARACTERISTICSOF STANDARD-FR~UENCY AND TIME-SIGNAL EMISSIONS IN THE ALLOCATEDBANDS Station Carrier I Time Signals Operation L~- Call Approximate Latitude :oordi- ~ Freauencies 'ewer Ofset 1 Accuracy/ Duration 100-ms Days Hours sign location Longitude MHz kW xio-lo/ XIO-9 1 I HZ Minutes Steps Week Day New Delhi 28" 34' N ATA IO 2 continuous 5 5 India 11" 19' E ___ ~~ ~ - Paris 48" 59' N -I- FFH 2.5 0.3 10/20 yes 2 8 1/2 France 2" 29' E ~~ Neuchatel 46" 58' N HBN 5 0.5 -300 0.1 yes 5/10 7 24 Switzerland 6" 57' E yes ___ Rome 41" 52' N IAM 5 1 0.5 yes lOjl5 yes 6 1 Italy 12" 27' E ~- Turin 45" 3'N 5 0.3 0.1 yes 35/60 6 1 113 IBF Italy 1" 40' E yes ~ 35" 42' N Tokyo 0.02 3 0.5 yes continuous 5 2 JGZAR Japan 139" 31' E yes Tokyo 35" 42' N 2.5; 5; IO; 15 2 -300 0.5 yes continuous yes 24 JJY Japan 139" 31' E Buenos 4ires 34" 31's LOL 5; IO; 15 2 -300 20 yes 4/60 5 Argentina 58" 21'W Yes 52" 22' N MSF Rugby 5, 5; 5; IO 0.5 -300 0.1 yes 5/10 yes 24 United Kingdom I" 11' w Prague 50" 1' N 2.5 I 24 OMA Czechoslovakia 14" 35' E Moscow 56" 37' N RWM-RES 5; 10; 15 20 7 19 U.S.S.R. 36" 36' E wwv Fort Collins 40" 41" 2.5; 20; 25 2.5 7 22 112 Colo. 105" 2.5' W 5; IO; 15 IO Hawaii 20" 46' N 2.5 1 7 22 1/2 WWVH U.S.A. 156" 28'W 5; IO; 15 2 Fort Collins 40" 41' N WWVL 0.02 1.8 1 24 Colo. 105" 3'W Lower Hutt 41" 14's ZLFS 2.5 0.3 1 3 New Zealand 174 55' E i 5o i 26" 11 ' S Johannesburg 10 0.25 1 24 zuo South Africa 28" 4'E Olifantsfontein 25" 58's 5 4 - 300 I 24 zuo South Africa 25" 14' E 351-828 TABLE I1 CHARACTERISTICS OF STANDARD-FREQUENCYAND TIME-SIGNAL EMISSIONSIN ADDITIONALBANDS I Station I Carrier I Time Signals Operation I I Call 1 Approximate Latitude Offset Accuracy Duration 100-ms Days Hours sign 1 location Longitude x Minutes Steps Week Day 1 x 1 1 1 Ottawa 45" 18' N ~ CHU 1335 ~ Canada 15" 45' w -300 1 5 1 yes continuous I yes 7 24 14670 DCF17 Mainflingen 50" 1'N 77.5 6 6 Germany 9" 9'W 1 I yes I Droitwich 52" 16' N 200 400 United Kingdom 2" 9'W 1 7 18-20 lo I 1 ~ 52" 22' N 1 Rugby -300 0.1 yes I 22 GBR United Kingdom 1" 11'W ) Prangins 46" N 75 0.02 yes continuous HBG I Switzerland 6" E 1 20 0.02 yes continuous yes I 24 ~~ Loran-C Carolina Beach 34" 4" I 24 1 N.C. 11" 55' w Rugby 52" 22' N -300 0.1 yes 5/10 ~ yes MSF IUnited Kingdom I" 11' w 1 1 1 I Cutler 39' 44" w -300 0.05 NAA 1 Me. 61" 17' W 24 9" 4'N 19" 39'W -300 1 0.05 1 yes Jcontinuous 1 yes I 24 48" 12' N I 24 21" 55' w Lualualei 21" 25' N yes 26.1 -300 0.05 NPM 1 Ha. 158" 9' W ! 1 1 24 NSS ~ Annapolis 38" 59' N -300 0.05 Md. 16" 21' W I 24 58" 8'N 1 yes 23 hours/day 50 15" 8'E I 24 55" 45' N 100 20 5 yes 40/120 nx 10 31" 33' E 1 1 21 I 59" 20' N ISX 104 0.06 LSweden 18" 3'E 1 2 Enkoping 59" 35' N SAZ 105 0.1 24 1 Sweden 11" 8'E 1 I Lyndhurst 38" 0's VNG 1 24 I Australia 145" 12' E 12005 WWVB Fort Collins 40" 40.5' N 1 yes continuous Colo. OS" 2.5" 1 0.: 1 I 1 7 24 Johannesburg 36" 11's zuo 1 South Africa 28" 4'E continuous 1 24 352-829 minute period. Within the ground-wave range, the Loran-C stations at 100 kHz provide signals with high stability at the receiver.
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