A time and frequency intercomparison experiment conducted using Earth stations in New Delhi, India and Raisting, FRG is described. The NPL clock was placed at New Delhi Earth Station and the Raisting Clock was calibrated with PTB/Primary standard via LORAN-C and travelling clocks. The random uncertainity of time comparisons, represented by two sample Allan Variance sigma (30 seconds), was less than 10 nanoseconds. The relative frequency difference between the NPL and Raisting Clocks, SNPL, RAIS, as measured over the 44 days period was found to be -15.7 x 10 to the -13th power. The relative frequency difference between PTB Primary Standard and Raisting Clock, SPTB, RAIS, during this period, was measured to be -22.8 x 10 to the -13th power. The relative frequency difference between NPL clock and PTB Primary Standard, SNPL, PTB, thus, is +7.1 x 10 to the -13th power. The clock rate (UTC, India) of +7.1 + or - 0.5 x 10 to the -13th power, agrees well with that obtained via VLF phase measurements over one year period and with USNO travelling clock time comparisons made in September, 1980

Banerjee, P.

Kumar, N.

Mathur, B. S.

Saxena, M.

Sood, P. C.

Suri, A. K.

English

NASA Technical Reports Server

PRECISE T & F INTERCCMPARISON BETWEEN NPL, INDIA
AND PTB, FEDERAL REPUBLIC OF. GERMANY
VIA SATELLITE SXMPHONIB-1
B.S.Mathur, P.Banerjee, P.C.Sood, Mithlesh Saxena,
Nand Kumar and A.K.Suri
Time and Frequency Section
National Physical Laboratory, Hillside Road,
New Delhi-110012,India.
ABSTRACT
In this paper we report a T & F intercomparison
experiment between the National Physical Labora-
tory (NPL), New Delhi, India and Physikalisch-
Technische Bundesanstalt (PTB), Federal Republic
of Germany, carried out from May 16 to June 29,
1979. The participating earth stations were
New Delhi, India and Raisting, FRG. The NPL
clock was placed at New Delhi Earth Station and
the Raisting Clock was calibrated with PTB/
Primary standard via LORAN-C and travelling
clocks. The random uncertainity of time compari-
sons, represented by two sample Allan Variance
OT (30 seconds), was less than 10 nanoseconds.
The relative frequency difference between the
NPL and aaisting Clocks,SNPL^AIS, as measured
 13
over the 44 days period was found to be -15.7x10" •
The relative frequency difference between PTB
Primary Standard and Raisting Clock,5PTB,RAIS, -^
during this period, was measured to be -22.8xlO~ •
The relative frequency difference between NPL
clock and PTB Primary Standard,SNPL,PTB, thus, is
+7.1x10-13.
The clock rate (DTC,India) evaluated in the
present work as +7.1 +_ O.SxlO-13, agrees very
well with that obtained via VLF phase measure-
ments over one year period described in a
companion paper and with USNO travelling clock
time comparisons made in September,1980.
863
https://ntrs.nasa.gov/search.jsp?R=19810018970 2020-03-21T12:58:18+00:00Z
INTRODUCTION
The French-German Satellite Symphonie-1 was made available
for Indian Telecommunication experiments from June 1977 to
June 1979. It was parked over the equator at 49°E longi-
tude. This group has earlier(1»2', in 10th and llth PTTI
Meetings, reported Clock Synchronisation and Time Dissemi-
nation Experiments in India by means of satellite Symphonie.
In this paper we report a simultaneous two way mode time
and frequency comparison experiment'3) by means of. satel-
lite symphonic between the atomic clocks at the National
Physical Laboratory (NPL), New Delhi and the time scale of
Physikalisch-Teschnische Bundesantalt (PTB) , Federal Repub-
lic of Germany. This experiment was performed over a 44
days period, from May 16 to 23 and then again from June 28
to 29,1979. The main objectives weres to synchronise UTC
(NPL) to that of U?C (PTB) and to find out the relative
frequency difference of NPL clocks, S^p^ prjB with respect
of PTB Primary Standard. ' '
The earth stations which participated in the experiments
were New Delhi earth station (DE3) where one of the NPL
cesium clocks, oscilloquartz Model 3200, hence forth
called NPL-1, was kept and the Raisting earth station (RES).
The other cesium clock at NPL, HP Model 5061A with option
004 hence forth called NPL-2 which participated in the
experiments and was at a different location was intercom-
pared with NPL-1 by regular rubidium clock transoortations.
The Cesium clock at Raisting earth station (HP Model 5061A
with option 004) was calibrated with PTB, Primary Standard
via LORAN-C and travelling clocks.
The theory and the measurement uncertainities of a simul-
taneous two way mode time transfer are well known^4' and
will not be described. Only the experimental details and
the results will be discussed.
DETAILS OF THE EXPERIMENTAL SET UP AT DES
The experimental set up at NPL is shown in Fig.l. It is
similar to the one used by Hubner and Hetzel(5)for time
comparisons performed by means of the satellite Symphonie
between Raisting(FRG) and Pleumeur-Bodou (France). The
1 PPS pulse from NPL-1 was placed on TV synch pulse as the
picture signal(wave form of the signal shown in Fig.l).To
have identical signal pattern throughout the duration of
864
the experiment a perfect phase and frequency synchronisation
between 1 PPS of Cs clock and TV sync pulse is required. To
achieve this, frequency of TV synch pulse generator was
locked to that of Cs clock and a definite phase relation
with 1 PPS of Cs clock was maintained.
As is clear from Fig.l the 1 PPS of NPL Cs clock was di-
rectly fed to "START" port of the time interval counter and
the signal was received from Raisting (Similar type of
pulse as shown in Fig.l) was directly used to "STOP" the
time interval counter.
Initially the data was taken once every second with a time
interval counter (HP 5248 L/M) of 10 nanoseconds resolution
as it could be interfaced with the available printer (HP
5050B). Later, in view of the better measurement uncertain-
ties, a counter (HP 5345A) with 2 nanoseconds resolution
was used and the data was taken once every 30 seconds. The
counter used at Raisting had a 1 nanosecond resolution.
RESULTS
Fig.2 shows a 30 minutes section of measurement values, as
obtained once every 30 seconds in New Delhi and Raisting.
The data was taken once every 30 seconds for about an hour
on each day. In Fig.2 the satellite motion has been elim-
inated by plotting first difference and only the deviations
from the straight line have been shown.
The random uncertainty for the upper curve, which is the
half difference of the measured values at New Delhi and
Raisting is + 4 nanoseconds. The mean half difference of
the measured"~values at New Delhi and Raisting along with
standard deviation and Allan Variance ((T =30 seconds) are
given in Table 1. Typical values of random uncertainties
are in the range of ± 3 to + 10 nanoseconds. In two cases,
values of even about + 70 nanoseconds were found. The
reasons for this larg"e uncertainty could not be ascertained.
The NPL-1, which was used in direct measurements with
Raisting, experienced a phase angle shift during the two
sets of data in May and June and a phase shift correction
of 564 ns with an estimated uncertainty of 20 ns, based on
the relative frequency difference of two NPL cesium clocks,
SNPL-1, NPL-2, was applied to the second set data of June.SNPL-1,NPL-2, measured by regular rubidium clock transporta-
tions during the experiment was found to be 22 ns/day,with
NpL-2 running faster than NPL-1.
865
The daily mean half difference of the measured values at
New Delhi and Raisting T (NPL-1 -Raisting) are plotted in
Fig.3. The slop of this curve gives the relative frequency
difference between NPL-1 and Raisting clock,SNPL,RAI5, as
measured over the 44 days period. The value in this case is
found to be -15.7+ 0.4xlO-13. In Fig.3 an expanded view
of first set of data is shown. The uncertainity shown is
the uncertainity of the slope of inclination of the regres-
sion line through the two sets of data points. The time
comparisons f(Raisting-UTC,PTB) between Raisting clock and
PTB primary standard during the above measurement period is
plotted in Fig.4. The slope of the curve gives the relative
frequency difference 3PTBjRAIS. The data for this curve was
made available* through the courtesy of PTB and is tabulated
in Table 2. Points on Fig.4 represent measurements via
LORAN-C and points with circle represent measurements via
travelling clock. SPTB,RAIS from Fig.4 is found to be
-22.3 + 0.3x10-23. From Figs. 3 and 4 the relative fre-
quency difference between NPL clock and PTB primary standard
SNPL.PTB (SNPL,RAJS-SPTB,RAIS), thus, is + 7.1 + 0.5xl(r13.
CONCLUSIONS
The time comparison made with U.S. Naval Observatory
travelling Clock brought to New Delhi in September 1980
agreed with the initial NPL-1 clock setting with respect
to PTB to within a small fraction of a microsecond and
with the NPL-PTB relative frequency differencejSNPLjPTB,
of + 7.1x10-13 to within few parts in 10"14) with those
measured by means of satellite symphonic*
Similarly,SNPL,PTB reported in this paper is^in good agree-
ment with the relative frequency difference ^l^PTB
7.0 + O.lxlO'^3 evaluated from VLF phase measurements over
one year period and described in a companion paper.
With this paper we conclude a series of time transfer and
time comparison experiments by means of satellite symphonie
which were initiated in April 1978 and were reported in
tenth and eleventh PTTI Meetings. The future plans on time
dissemination via satellites include some more experiments
with Indian experimental satellite APPLE (to be launched
in mid 1981), a time dissemination service via operational
Indian demostic satellite INSAT to be launched in late 1981,
involvement in IASSO/SIRIO-2 experiments and possibilities
of international time comparisons via some common view
satellites*
866
The intercalibratlons between PTB and Raisting clocks were
made via LORAN-C and travelling clocks. Four time compari-
sons were made during this period via travelling clocks
with an estimated uncertainty of + 50 ns. The EORAN-C
measurements were more uncertain than these.
A basic limitation, contributing maximum uncertainity, of a
two-way time transfer via satellite is the precise measure-
ment of individual path delay of transmitter and receiver.
At New Delhi no attempts were made to measure individual
path delay of transmitter and receiver. Only combined loop
delay consisting of transmitter, test loop translator (a
replica of transponder on satellite) and receiver was mea-
sured. This gave a value of 1900 + 10 nanoseconds. PTB has
communicated separate measurements~"on path delay of trans-
mitter and receiver at Raisting earth station. These,
including filter delays, are :
Transmitter (Raisting) i 956 ns
Receiver (Raisting) : 954 ns
Total :1910 ns
It may be seen that total path delays encountered at New
Delhi and Raisting are same with transmitter and receiver
contributing half of the total delay.
A clock transport between NPL and PTB during the experiment
was not possible for financial reasons and the uncertainity
of time comparisons could not be ascertained. However,
based an equality of path delays at Raisting and New Delhi,
with transmitter and receiver delay being almost equal, one
could infer 100 nanoseconds as the upper limit for accuracy
uncertainty of time comparisons. These include time trans-
fer uncertainity between PTB and Raisting 0^50 ns), time
transfer uncertainity between NPL-1 and NPL-2(^20ns) and
uncertainity in path delays (A/100 ns).
The Relativistic Correction^6) due to earth's rotation for
the NPL-PTB time comparison experiment is calculated to be
+• 179.5 ns. This value should be added to column 3(mean
value) of Table 1 to get the true value for the time dif-
ference between Raisting and NPL. It is a significant
contribution in view of the precision of less than 10 ns
achieved in the experiment. However, in absence of travel-
ing clock time comparison, this could not be verified.
867
ACKNOWLEDGEMENTS
First of all we will like to thank Prof.G.Becker of
Physikallsche-Teschnische Bundesanstalt for agreeing to do
the experiment and for allowing us to publish the results.
We are grateful to Mr.B.Fisher and Dr.P.Hetzel for their
help in the successful completion of the experiment and
for supplying us the PTB-Raisting data used in this experi-
ment. Without Mr.J.Jahreis at the Raisting earth station
and Mr.M.L.Haslja at New Delhi earth station the experiment
was just not possible. We are thankful to other staff
members at New Delhi earth station for their most valuable
suggestions and to Dr.A.Sen Gupta of NPL for his careful
study of the manuscript of this paper and valuable sugges-
tions.
We express our gratitude to STEP Management Board and
Symphonie Utilisation Group for their approval and assis-
tance for the experiment.
Finally, it is always a great pleasure to acknowledge the
advise and encouragement received from Dr.A.R.Verma,Director,
National Physical Laboratory, New Delhi, India.
REFERENCES
1. Somayajulu, Y.V., Mathur, 3.S., Jain, C.L., Banerjee,
P., Garg, S.C., Singh, L.. Sood, P.C., and Tyagi,
T.R., "Clock Synchronisation Experiments in India
Using Symphonie Satellite" Proc. Tenth PTTI Meeting,
November, 1973.
2. Mathur, B.S., Banerjee, P., Sood, P.O., Saxena,
Mithlesh, Nand Kumar, Suri, A.K., Jain, C.L. and
Kumar, K. ,"A Study of Time Dissemination Via Satellite
in India" Proc. Eleventh PTTI Meeting, November,
1979.
3. Becker, G., Fisher, 3., Hetzel, P., Mathur, B.S.,
"Time and Frequency Comparisons by means of Syraphonie"
Paper presented at Seminar on Symphonie held at
Berlin in February, 1930.
868
4. Brunet, M., "Two-way Time Transfers Between National
Research Council (Ottawa) and Paris Observatory via
The Symphonie Satellite", Paper presented at Seminar
on Symphonie held at Berlin In February,1930.
5. Hubner, U., Hetzel, P., "Zweiweg-Zeltvergleich mit
dem Satellten Symphonie11, Kleinheubacher Berichte
Vol. 21, pp 459-468, 1978.
o. Mathur, B.S., Saxena, G.M., "Relativistic Correction
for the NPL (India) - PTB (West Germany) clock
Synchronisation Experiments11, Indian Journal of Pure
and Applied Physics, Vol.18, No.8, pp. 601-603,1980
and Private Communication with PTB.
869
Table 1
TIMS COMPARISONS BETWEEN RAISTING'S CLOCK AND
UTC(PTB) VIA LORAN-C AND TRAVELLING CLOCK.
Date . MJD T(Raisting-DTC TUais ting-UTC
(PTB) by clock (PTB) via
transportation LORAN-C( us ) ( us )
14.05.79
15.05.79
17.05.79
13.05.79
21.05.79
22.05.79
23.05.79
30.05.79
31.05.79
01.06.79
05.06.79
07.06.79
03.06.79
09.05.79
13.05.79
19.06.79
20.06.79
21.05.79
23. 06 i 79
29.06.79
44007 0,357
44009
44010
44011
44014
44015
44015
44023
44024
44025
44030 4,113
44031
44032
44033
44042
44043 6,638
44044
44045
44052
44053 3,705
0,050
0,304
0,497
1,092
1,415
1,527
2,955
3,034
3,350
4,136
4,342
4,709
4,752
5,519
5,630
6,903
7,153
3,469
3,730
870
Table 2
TIME COMPARISONS, STANDARD DEVIATION AND
ALLAN VARIANCE BETWEEN RAISTING'S CLOCK
AND NPL-1 VIA SATELLITE SYMPHONIE
Date
May 16 '79
May 17' 79
May 18 '79
May 21 '79
May 22 '79
May 23 '79
June 23 '79
June 29 '79
MJD
44009
44010
44011
44014
44015
44016
44052
44053
Mean
Value
* **
- 6.0 ns
+ 104. 7ns
+263. 7ns
•••698.8ns
+ 746. 9ns
+951. 5ns
+5067.0 ns
+5401.2 ns
Standard
Deviation
20.2 ns
10.96 ns
7.92 ns
4.24 ns
62.52 ns
7.91 ns
33.4 ns
3.5 ns
Allan
Variance
= 30 Sec.
4*4141
4.4 ns
10.5 ns
10.3 ns
3.3 ns
65.1 ns
2.8 ns
60.5 ns
4.73ns
* Positive sign indicates Raistings 1 PPS coming earlier
than NPL 1 PPS.
** NPL Time was off by 436.2943 us and was set after the
experiment on May 16'79.
*** For limited number of observations.
871
-f't PTB
I s.p.G.a I£y=a=-i=E
UONOSHOT
I*. 20Jill
CESIUM-CLOCK
EXPERIMENTAL SET-UP OF NPL-PTB CLOCK SYNCHRONISATION
E XPERMENT (MAY - JUNE, 1979)
S.P.G. = Synch pulse generator
Fig. 1
t 96O
rf 940
61
,_ 0 550
| a 540
t> i
H| 560
| 550
« 54O
|
S t -
NPL-PTB CLOCK SYNCHRONISATION EXPERIMENT MAY-JUNE-, 1979.
10 15 20 25
Fig.2 : Deviations froa the straight line of
Clock off-set between NPL and Raisting,
872
;ooo
0 IO CO JO 40 SO «0
NPL-PTB CLOCK SYNCHRONSATION EXPERIMENT
MAY-JUNE,1979
Fig.3 : Clock off-set between NPL and
Raisting (3NPL,RA!S).
10,00
z>000
£7000
9,
Poiflls rtprtitflt mcoiurcfnantt vio LORAN-C
Poiflti vith circle ffprtMnlt m«atirt«Mnl« «io
Pavtofelc clock.
4O 9010 20 JO
M JO-44000 T~*
NPL-PTB CLOCK SYNCHRONSATION EXPERIMENT
MAY-JUNE, 1979
Fig. 4: Clock off-set between PT3 and
Raisting (SpTB,RAIS)..
873
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Precise time and frequency intercomparison between NPL, India and PTB, Federal Republic of Germany via satellite symphonie-1

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