Various methods presently used for the dissemination of time at several levels of precision are described along with future projects in the field. Different aspects of time coordination are reviewed and a list of future laboratories participating in a National Time Scale will be presented. A Brazilian Atomic Time Scale will be obtained from as many of these laboratories as possible. The problem of intercomparison between the Brazilian National Time Scale and the International one will be presented and probable solutions will be discussed. Needs related to the TV Line-10 method will be explained and comments will be made on the legal aspects of time dissemination throughout the country

Silva, I. M.

Silva, P. M.

English

NASA Technical Reports Server

THE PRESENT DEVELOPMENT 
~ 7 5  27181 
OF TIME SERVICE IN BRAZIL, WITH 
THE APPLICATION OF THE TV LINE-10 METHOD FOR 
COORDINATION AND SYNCHRONIZATION OF ATOMIC CLOCKS 
Paul0 Mourilhe Silva and Ivan Mourilhe Silva 
Obse rvator io Nac ional 
Rio de Janerio, Brazil 
ABSTRACT 
A short historical review will be followed by a description of the re- 
sources available at the Time Service of the National Observatory. 
Various methods presently used for the dissemination of time at sev- 
eral levels of precision will be described along with future projects 
in the field. Different aspects of time coordination will be reviewed 
and a list of future laboratories participating in a National Time Scale 
will be presented. A Brazilian Atomic Time Scale will be obtained 
from as many of these laboratories as possible. The problem of in- 
tercomparison between the Brazilian National Time Scale and the In- 
ternational one will be presented and probable solutions will be dis- 
cussed. Needs related to the TV Line-10 method wil l  be explained 
and comments will be made on the legal aspects of time dissemination 
throughout the country. 
Following this there will be a description of measurements taka be- 
tween two laboratories, ONRJ and INPE . A comparison will be made 
between these measurements and those obtained in 1969 and 1970 by 
the NAFS and USNO in the U.S.A. Finally, a comparison will be 
made between the Line-10 and the physical clock transportation meth- 
ods. The comparisons show good promise for the effectiveness of the 
Line-10 method in Brazil. 
I - SHORT HISTORICAL NOTE 
The Time Service of the National Observatory of the Ministry of Education and 
Culture, active since 1847 is specifically dedicated to the countrywide dissem- 
ination and determination of Legal and Astronomical Time in Brazil. 
In 1902 our Time Service obtained time by solar and certain star meridian pas- 
sages and maintained time by pendulum and chronometers. Time transmission 
for public use was visible by the release of a balloon from a small tower on the 
terrace of the Observatory on a hill near the center of Rio de Janeiro. 
99 Preceding page 
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The law n? 2784 of June 18,1913 that established legal time in Brazil and adopted the 
time zones, which was regulated by the Decree n? 10.546 of November 5, 1913 
is still valid. It determined that the National Observatory of Rio de Janeiro , as well 
as future stations that may be designated, are responsible for the determination 
of time and its transmission for geographical and navigational purposes by tele- 
graphic or  "Time Ball" means , in agreement with the accepted and valid inter- 
national agreements. 
On June 1, 1918 the first radio-telegraph station of time signals was inaugurated. 
They were transmitted twice daily, from 13h 55m 55s to14hOOmOOs, andfrom 
23h 55m 55s to OOh 00m O O s ,  GMT. 
The operation of the Observatory was regulated by Decree n? 6361 of October 1, 
1940 which established that: 
Chapter III, Art. 7 - The Division of Meridian Services and attached 
Services, will determine and transmit legal time by radio-telegraphy 
in accordance with decisions of the International Time Committee, 
with the adequate precision not only for the purposes of navigation, 
but for engineers and the public and also, in cooperation with the 
Bureau International de l'Heure, for Universal Time determination: 
With these fundamental objectives operating since the time of the Empire (before 
1889) several techniques and varied instruments have been used by generations 
to cooperate with the Time Service, beginning with pendulums and arriving at 
the present status where everything depends on atomic clocks, 
11 - ACTUAL SYSTEM 
We are now in a transition state in which we are trying to solve our problems of 
time dissemination for both scientific and non-scientific users. W e  are only begin- 
ning to adapt to our conditions , some techniques previously usedby other countries. 
Of course this adaptation implies, in all cases, an investigation of the methods of 
allpossible theoretical and practical considerations. It is possible that we must 
develop new techniques more useful to our particular conditions in South America. 
For this purpose we have had pendulum clocks, clocks with crystal oscillators 
and more recently commercial Cesium and Rubidium frequency standards. 
To establish a time scale based on as many standards as possible, we began in 
December 1972 making comparisons between all available standards using one 
of our Rubidium standards as a portable clock. 
100 
We know of course, that the Rubidium standard is not the best choice for a port- 
able clock, and we intend as soon as possible to get a Cesium for this purpose. 
In July of last year, 1973, we started the comparisons between standards located 
in Rio and two places in Sao Paul0 using the Line-10 method. Initially we stud- 
ied the observed flucuations in the propagation delay in the path. The two loca- 
tions now used are approximately 300 and 450 km from Rio. More experiments 
are being made at Brasilia, Belem, Nata l  and Manaus, which are far from Rio 
at straight distances of 900; 2470; 2170 and 2820km respectively. 
At  present, we have in Brazil a 'Working Group on Time" that, with the coordina- 
tion of "National Observatory" and sponsored by our "National Research Con-  
cil, has regular meetings. All  the Brazilian institutes that have atomic clocks 
participate in the Brazilian time scale. 
For the dissemination of time and frequency we are now using broadcast trans- 
missions in HF (Short waves) and VHF. We know the limitations involved by 
these bands. For precision comparisons of time or frequency we normally go 
with our Rubidium to the users that require such precision, o r  they come to us, 
o r  we have a connection by telephone line, depending on the frequency. 
We are now installing in our capital of Brasilia, a new time service station. We 
intend in the next year to begin transmissions of time signals and standard fre- 
quencies using the advantage that Brasilia is more or  less a central point in 
Brazil. We have started experimental transmissions, using the help of a govern- 
ment broadcasting station, that is putting high power transmitters of 250kw and 
300kw into operation. 
Using the facilities of our Brazilian Telecommunication Company, EMBRATEL, 
that has a microwave link along the entire coast, we will retransmit by new coast- 
a l  stations, (16) time signals, that are useful for the ships communicating with 
those stations. 
Normally in some transmissions of Time signals, for users of low precision we 
transmit voice announcements of time every 10 seconds. These announcements 
are generated from automatic equipment which is synchronized with our Cesium 
standard. 
W e  have daily reception of Time signals from other countries in VLF, HF and 
VHF , (Dwo years ago, during the experimental transmission of the ATS-3 satellite). 
In the near future, we intend to have regular comparisons between the Brazilian 
time scales and the International time scales using portable clocks and/or recep- 
tion of signals transmitted from satellites. 
101 
IXI - LINE-10 ZMETHOD IN BRAZIL 
EMBRATEL 
UFRJ 
ON 
INPE 
LAG 
CRAAM 
As there are now or soon will be, various laboratories with atomic frequency 
standards (commercial @-pes only) in Brazil, itwasdecided by the GTH (fWork- 
ing Group on Time, created by the National Research Council) that the National 
Observatory would initiate experiments to obtain a national standard time scale 
from the individual scales of the several laboratories. 
~ 
Cs (1) H P  
C s  (1) Ebauche 
Cs  (2) HP. Rb (2) H P  and Tracor 
C s  (1) H P  
C s  (1) Ebaushe; Rb (1) Sulzer 
Cs (1) HP, Rb (2)  Tracor 
Table 1 presents a list of these laboratories and Figure 1 presents the map of 
Brazil with their locations. Because of the dimensions of Brazil (more o r  less 
3200km in the N-S direction and 4200km in the E-W direction) line-10 will be 
the most useful method available for comparisons. 
TABLE I 
POSSIBLE AND ACTUAL PLACES USING THE LINE-10 METHOD 
City -State 
Rio de Janeiro-GB 
S. Jose dos Campos-SP 
S. Paulo-SP 
Atibaia-SP 
EMBRATEL - Brazilian Telecommunication Corporation 
UFRJ - Federal University of Rio de Janeiro 
INPE - Space Research Institub 
IAG - Astronomical and Geophysical Institute of S. Paul0 University 
CRAAM - Radio Astronomy and Astrophysical Center of Mackenzie 
The experiments were started with measurements between INPE (Space Research 
Institute) and ONRJ (National Observatory of Rio de Janeiro) which are approxi- 
mately 3 0 0 b  apart. 
ONRJ versus INPE 
The measurements are made twice per week for six minutes each day. A s  there 
is transmission in both directions, measurements are made during three minutes 
in each direction. This system allows determination of propagation delay between 
the two laboratories. 
102 
Only 30 measurements are used for the reduction of the measurements made 
during the 3 minutes. 
The reduction actually is made by means of a small table calculator, and when 
more laboratories start to participate we will use a PDP8/E from Digital Equip- 
ment Corp. (DEC). 
Figure 2 presents the results for ONRJ-INPE in comparison with the result of 
NAFS-USNO comparison, in terms of the Allan variance. 
We can observe that our result is more or less ten times worse that the other. 
We think that this is because we are comparing only two Ringle standards, 
whereas the NAFS-USNO is a comparison between two scales resulting from sev- 
eral standards each. Another difference between the two results is in the num- 
ber of data points; our situation covers only one 100 day interval. 
Another result is also presented. 
Parallel to the Line-10 measurements, we make physical transportation of 
clocks for precise measurements of propagation delay. Figure 3 presents this 
comparison. 
Following are observations on this figure. 
a - the line-10 values are not as dispersed in the JUL-OCT interval as in the 
Nov-Mar interval. This may be due to the rain precipitation that is more 
pronounced in the latter period. 
i 
b - in the end of November there was a sudden change in the relative frequency 
because of a failure in one of the two clocks. 
e - the variation, -1.5 x 10-12 and +l. 0 x is in agreement with the specifi- 
cation of the two standards, which is f5 x 10-12. 
d - propagation delay in this experiment is of no importance because its varia- 
tions, over one year, is of the order of io. 3 p s  . 
\ 103 
REFERENCES 
1. Jespersen, J. L., Fey L., "Time-telling Techniques," IEEE Spectrum, 
May 1972. 
2. Anuario do Observatorio Nacional para o an0 de 1919, Rio de Janeiro, Im- 
prensa Nacional. 
Annuaire 1971 du Bureau des Longitudes, Gauthier, Vil lars  Editeur, Paris, 
Franca. 
3. 
4. Frequency and Time Standards, Application Note 52, Hewlett Packard Co. 
5. Smith, H. M., "International Time and Frequency Coordination," Proc. 
IEEE, May 1972. 
6. Silva, I. M. , Silva, P. M. , "CoordenaqZo da Hora no Brazil, 
no 2 do Serviqo da Hora do Observatorio Nacional, Rio de Janeiro. 
PublicaqZo 
7. Bechler, R. E. , "A Historical Review of Atomic Frequency Standard,'' 
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104 
15. D. H. Andrews, C. Chaslain and J. DePrins, "Reception of Low Frequency 
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52, August 1971. 
18. D. W. Allan, B. E. Blair, D. D. Davis and H. E. Machlan, "Precision 
and Accuracy of Remote Synchronization via Network Television Broad- 
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press. 
D. H. Phillips, R. E. Phillips, and J. J. O'Neil, "Time and Frequency 
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19. 
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vol. 54, n? 2. 
21. Barnes, J. A. et  al. , Y%aracterization of Frequency Stability, 
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NBS 
105 
J a n t  
Figure 1. 
1 ro  
Figure 2. Sampling time (7 )  in days 
106 
I ' 4 0 d '  I 
ONRJ-USNO 
-1 .2x lO 
/ 
L I 1973 1974 I 
Figure 4. Global comparisons 
107 


The present development of time service in Brazil, with the application of the TV line-10 method for coordination and synchronization of atomic clocks

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