Time comparisons were made between cesium clocks in Yugoslavia and other cesium clocks in the country by the Laboratory of Federal Bureau of Measures and Precious Metals. Regional standard frequency and time signals dissemination is over National TV network by so called active TV system. International comparisons are performed via Loran-C system and by clock transportation. The method of calculation and approximation of the time signal propagation delays is given. Settled comparison results of the cesium clocks via TV network, Loran-C, and by clock transportation are also discussed in this paper

Hajdukovic, S.

Markovic, Z. M.

Breton 

NASA Technical Reports Server

THE TIME AND FREQUENCY COMPARISONS V I A  LORAN - C 
AND NATIONAL TV NETWORK I N  YUGOSLAVIA 
Zoran M. Markovie and S t i j e p o  Hajdukovie  
F e d e r a l  Bureau of  Measures and P r e c i o u s  Meta l s  
Mike Alasa  14 ,  11000 Be lg rade ,  Yugos lav ia  
ABSTRACT 
Many y e a r s  comparison r e s u l t s  o f  t h e  cesium 
c l o c k s ,  which a r e  done i n  t h e  Labora to ry  of  
F e d e r a l  Bureau o f  Measures and P r e c i o u s  Me ta l s  
a r e  p r e s e n t e d  i n  t h i s  pape r .  Regiona l  s t a n d a r d  
f requency  and t i m e  ~ i g n a l s  d i s s e m i n a t i o n  i s  
o v e r  N a t i o n a l  TV n-!-work by s o - c a l l e d  a c t i v e  
TV system. I n t e r n a t i o n a l  comparisons a r e  pe r -  
formed v i a  Loran-C system and  by c lock  t r a n s -  
p o r t a t i o n .  
The way o f  c a l c u l a t i o n  and approximat ion  of  t h e  
t i m e  s i g n a l  p ropaga t ion  d e l a y s  i n  t h e  aim 01 
t h e  c l o c k s  comparisons is  g i v e n .  S e t t l e d  compa- 
r i s o n  r e s u l t s  o f  t h e  cesium c l o c k s  v i a  TV n e t -  
work,  Loran-C, b o t h  o f  them and by c l o c k  t r a n s -  
p o r t a t i o n  a r e  a l s o  d i s c u s s e d  i n  t h i s  p a p e r .  
The aim o f  comparison and s y n c h r o n i s a t i o n  is  t o  
form and m a i n t a i n  t h e  Yugoslav t i m e  s c a l e .  The 
p r e s e n t e d  v a l u e s  of  t h e  UTC - UTC(YUZM) show t h e  
s t a b i l i t y  of  f rcquency  comparisons of  1 0 - l ~  f o r  
t h e  p r e s e n t e d  p e r i o d .  
INTRODUCTION 
I n  t h e  Labora to ry  o f  Fede ra l  Bureau o f  Measures and P r e c i o u s  
Metals t h e  Yugoslav pr imary s t a n d a r d  o f  t i m e  and  f r equenzy  is  
ma in t a ined  f o r  more than  e i g h t  y e a r s .  I t  c o n s i s t s  of  cesium beam 
t u b e  s t a n d a r d  and a rubidium g a s  c e l l  s t a n d a r d  a s  a backup. Com- 
p a r i s o n s  o f  o u r  pr imary  s t a n d a r d  i s  c a r r i e d  o u t  w i t h  t h e  i n t e r n a -  
t i o n a l  c l o c k s  a s  w e l l  a s  w i t h  t h e  cesium c l o c k s  owned by c e r t a i n  
https://ntrs.nasa.gov/search.jsp?R=19850020936 2020-03-22T19:43:08+00:00Z
i n s t i t u t i o n s  i n  Yugos lav ia .  These comparisons a r e  v i a  Loran-C 
sys tem,  N a t i o n a l  TV network and by c l o c k  t r a n s p o r t a t i o n .  
The measurement p r o c e s s  o f  comparisons is  f u l l y  au toma t i sed  b y  
u s i n g  t h e  microcomputer which i s  f o r  o u r  purposes  made i n  Yugo- 
s l a v i a .  I n  t h a t  way t h e  measurements o f  a p p r o p r i a t e  t: ',-, i n t e r -  
v a l s  have been c a r r i e d  o u t  e v e r y  day a y e a r .  
The TV s t u d i o  Be lg rade ,  Yugoslavia  began o v e r  t e n  y e a r s  ago  t h e  
e x p e r i m e n t a l  t r a n s m i s s i o n  of  t i m e  and s t a n d a r d  f requency  s i g n a l s  
by u s i n g  t h e  s o - c a l l e d  a c t i v e  TV sys tem,  which s e c u r e s  t h e  Time 
of  Coinc idence  e v e r y  second.  I n  t h i s  sys tem,  second p u l s e s ,  s t a n -  
d a r d  f requency  and t h e  coded t i m e  of  day a r e  a l l  d e r i v e d  from t h e  
cesium c l o c k  which i t s e l f  i s  l o c a t e d  w i t h i n  t h e  TV s t u d i o  premis-  
s e s . .  The p r i n c i p l e s  o f  t h i s  system was r e p o r t e d  on I X  PTTI, No- 
vember 1977. 11) 
CT'3CK COMPARISONS 
Ia:,r o u r  UTC t i m e  comparison w e  used t h e  s i g n a l s  t r a n s m i t t e d  from 
t h e  m a s t e r  s t a t i o n  o f  Medi te r ranean  Sea c h a i n  o f  Loran-C sys tem 
i n  S e l l i a  Marina,  I t a l y .  I n  o u r  everyday  work w e  compare t h e  c l o c k  
i n  o u r  Labora to ry  and t h e  clo~:!; i n  TV s t u d i o  Belgrade  (TVB) w i t h  
mas t e r  c l o c k  o f  Medi te r ranean  Sea  c h a i n ,  F i g u r e  1 ,  v i a  Loran-C 
system. A l so ,  v i a  TV network o u r  c l o c k  is compared w i t h  c l o c k  i n  
TV s t u d i o  Belgrade .  
F i g u r e  2 .  shows Coord ina t ed  Universal .  Time o f  o u r  Labora to ry  
UTC(YUZM) r e l a t i v e  t o  UTC ( B I H )  f o r  1000 days  a t  t h e  i n t e r v a l s  of  
t e n  days  a s  it would be s e n t  t o  B I H .  
The o r i g i n  o f  Coord ina ted  U n i v e r s a l  T i m e  (UTC) S c a l e  of  t h e  Fede- 
r a l  Bureau o f  Measures and P r e c i o u s  Me ta l s  o f  Yugos lav ia  UTC(YUZM) 
is  de te rmined  w i t h  t h e  d i x e c t  measurement by c l o c k  t r a n s p o r t a t i o n  t . .  
i n  Geneve, S w i t z e r l a n d  on December 21,  1981 ( M J D  44959.59).  
The second d i r e c t  measurement o f  UTC(0P) - UTC(YUZM1 by c l o c k  
t r a n s p o r t a t i o n  was i n  P a r i s ,  France  from June  26,  1934 ( M J D  45877.8) 
till June  2 9 ,  1984 ( M J D  45880.4) .  The t i m e  d i f f e r e n c e  on M J D  45877.8 
was UTC(0P) - UTC(YUZM) = -61.9 p s .  With t h i s  d i r e c t  measurement 
t h e  c a l c u l a t e d  v a l u e  of  t h e  t o t a l  t i m i n g  d e l a y  of Loran-C s i g n a l s  
h a s  been e x p e r i m e n t a l l y  provzd a g a i n .  For  t h e  p e r i o d  o f  o u r  e x p e r i -  
menta l  work, b e f o r e  t h e  c l o c k  t r a n s p o r t a t i o n  to Geneve w e  u sed  t h e  
c a l c u l a t e d  v a l u e  o f  t o t a l  t i m i n g  d e l a y  f o r  Loran-C s i g n a l s  which 
h a s  been c a l c u l a t e d  i n  o u r  Labora to ry  u s i n g  USNO r ~ c o m e n d a t i o n s  and 
M i l l i n g t o n  method f o r  secondary  phase c o r r e c t i o n s .  1 2 )  
To t h e  d a t a  o b t a i n e d  by t h e  t i m e  i n t e r v a l  c o u n t e r  measurements w e  
a p p l i e d  t h e  c o r r e c t i o n s  from USNO d a i l y  phase v a l u e s  and t i m e  d i f -  
f e r e n c e s  S e r i e s  4 of  UTC(tJSN0-MC) - Medi te r ranean  Sea  c h a i n  and 
from B I H  C i r c u l a r  D o f  VTC - UTC(USN0-MC). A l so ,  w e  s u b t r a c t e d  t h e  
v a l u e  o f  t o t a l  t i m i n g  d e l a y  w i t h  t h e  assumption t h a t  t h e  propaga- 
t i o n  d e l a y  between the Loran-C t r a n s m i t t e r  and o u r  r e c e i v e r  a r e  
c o n s t a n t  f o r  t h e  tine o f  o b s e r v a t i o n .  
The d a t a  p l o t t e d  on t h i s  f i g u r e  i n c l u d e  t h e  r e l a t i v e  p h a s e  va r i -  
a t i o n s  o f  r e c e i v e d  Loran-C s i g n a l s  and  t h e  f r e q u e n c y  d r i f t  o f  o u r  
c l o c k .  From t h a t  d a t a  o n e  c a n  o b s e r v e  t h e  s e a s o n a l  v a r i a t i o n s  o f  
t h e  p h a s e  o f  t h e  r e c e i v e d  s i g n a l s ,  which  i s  t h e  mos t  s t a b l e  i n  
summer. The maximum v a l u e  o f  t h e  t i m e  d i f f e r e n c e  between t h e  p l o t -  
t e d  d a t a  and t h e  a p p r o x i m a t e d  mean is  2 . 5  us ,  a n d  f o r  t h e  l a s t  
y e a r  it is  t y p i c a l l y  less t h a n  0.5 u s .  From t h i s  it i s  o b v i o u s  
t h a t  t h e  long- te rm s t a b i l i t y  i s  b e t t e r  t h a n  10-13.  
I n  t h i s  p a p e r  t h e  compar i son  o f  ces ium c l o c k s  u s i n g  t h e  t i m e  t r a n -  
s m i s s i o n  o f  t h e  a c t i v e  TV s y s t e m  is  a l s o  a n a l y s e d .  '.The d i f f e r e n c e s  
o f  t i m e  t r a n s m i t t e d  by  TV B e l g r a d e  r e l a t i v e  t o  t h e  UTC(YUZM)  f o r  
1040 d a y s  a r e  shown i n  F i g u r e  3 .  The v a l u e  o f  f r e q u e n c y  d r i f t  o f  
t h e  c l o c k  i n  o u r  L a b o r a t o r y  is  removed f rom t h e  d a t a ,  a n d  t h e  
d r i f t  shown on t h i s  f i g u r e  i s  of t h e  c l o c k  i n  TV s t u d i o  E e l g r a d e .  
T o g e t h e r  w i t h  t h e  e v e r y  d a y  c o m p a r i s c n s  of o u r  c l o c k  w i t h  t h e  
c l o c k  i n  TV s t u d i o  B e l g r a d e  v i a  TV n e t w o r k ,  c l o c k  t r a n s p o r t a t i o n s  
i n  c e r t a i n  t i m e  i n t e r v a l s  ( o n c e  y e a r )  i s  u s e d .  The o r i g i n  o f  
t i m e  s c a l e  which is t r a n s m i t t e d  v i a  TV ne twork  i s  d e t e r n i n e d  by  
c l o c k  t r a n s p o r t a t i o n .  D u r l n g  t h e  c o m p a r i s c n s  b y  c l o c k  t r a n s p o r t a -  
t i o n  c e r t a i n  s t e p  t i m e  c o r r e c t  i o n s  a r e  i n t r o d u c e d  i n  o r d e r  t o  
m a i n t a i n  t h e  t r a n s m i t t e d  t i m e  w i t h i n  t h e  + 30 p s  r e l a t i v e  t o  t h e  
UTC(YUZM). By c l o c k  t r a n s p o r t a t i o n  t h e  c a i c u l a t e d  v a l u e  of  t o t a i  
t i m i n g  d e l a y  o f  TV s i g n a l s  i s  e x p e r i m e a t a l l y  p r o v e d .  
Data  f o r  AT a r e  p l o t t e d  a t  t h e  i n t e r v a l s  o f  t e n  d a y s  and t n e y  
i n c l u d e  t h e  r e l a t i v e  p h a s e  v a r i a t i o n s  o f  t h e  s i g n a l s  r e c e i v e d  v i a  
TV ne twork .  
Compar isons  o f  t h e  c l o c k  i n  TV s t u d i o  Be1~;rade u s i n g  t h e  M e d i t e r -  
r a n e a n  S e a  chair1 o f  t h e  Loran-C s y s t e m  and  t h e  N a t i o n a l  TV n e t w o r k  
o b t a i n  t h e  d i f f e r e n c e  o f  UTC - UTC(TVB). F i g u r e  4 .  shcws t h e  t i m e  
d i f f e r e n c e  o f  UTC(TVB) r e l a t i v e  t o  UTC(B1H) f o r  1000 d a y s .  To the 
d a t a  p l o t t e d  a t  t h e  i n t e r v a l s  o f  t e n  d a y s  a x e  a p p l i e d  t h e  c o r r e c -  
t i o n s  from USNO S e r i e s  4 and  BIH C i r c u l a r  D i n  t h e  same way as it 
i s  p r e v i o u s l y  d e s c r i b e d .  The i n t r o d u c e d  s t e p s  i n  t r a n s m i t t e d  t i m e  
were removed f rom t h e  d a t a  by  c a l c u l a t i o n  i n  o r d e r  t o  make e a s i e r  
o b s e r v a t i o n  o f  r e l a t i v e  p h a s e  v a r i a t i o n s  o f  t h e  s i g n a l s  r e c e i v e d  
v i a  Loran-C a n d  TV n e t w o r k .  On t h i s  d a t a  t h e r e  i s  n o  i n -  u e n c e  o f  
t h e  p e r f o r m a n c e  o f  t h e  c l o c k  i n  o u r  L a b o r a t o r y ,  a n d  t h e  :'nown 
d r i f t  i s  o f  t h e  c l o c k  i n  TV s t u d i o  B e l g r a d e .  
On t h a t  way, b y  s i m u l t a n e o u s  c o m p a r i s o n s  o f  c l o c k s  o v e r  e a c h  
t r a n s m i t t i n g  p a t h ,  t h e  p a r t i c u l a r  p e r f o r m a n c e  o f  e a c h  c t s i u m  
c l o c k  c a n  b e  d i s t i n g u i s h e d  as w e l l  a s  t h e  i n f l u e n c e  o n  s t a b i l i t y  
o f  t h e  p a r t i c u l a r  t r a n s m i t t i n g  p a t h .  The s t a n d a r d  d e v i a t i o n  ( l o )  
measured by  t h e  c o u n t e r  i s  t y p i c a l l y  1 0  - 1 8  n s  f o r  t h e  compar i -  
s o n s  v i a  Loran-C and TV n e t w o r k ,  7 - 11 n s  f o r  t h e  c o m p a r i s o n s  
v i a  Loran-C s y s t e m  a n d  7 - : O  n s  f o r  t h e  c o m p a r i s o n s  v i a  TV n e t -  
work. Due t o  t h e  change  o f  o u r  TV r e c e i v o x  set w i t h  t h e  newly 
d e s i g n e d  one  t h i s  s t a n d a r d  d e v i a t i o n  f o r  t h e  compar i sons  v i a  TV 
network i s  now 3 - 6 n s .  Hence,  it can  b e  d i s t i n g u i s h e d  which  
t r a n s m i t t i n g  p a t h  h a s  t h e  g r e a t e r  u n c e r t a i n t y .  
CONCLUSION 
I n  F e d e r a l  Bureau o f  Measures and P r e c i o u s  Metals t h e  i n t e r n a t i -  
o n a l  compar i sons  o f  o u r  ces ium c l o c k  are per formed  v i a  Loran-C 
and b y  t h e  c l o c k  t r a n s p o r t a t i o ~ ,  and v i a  N a t i o n a l  TV ne twork  it 
is  c ~ m p a r e d  w i t h  o t h e r  cesium c l o c k s  i n  t h e  c o u n t r y .  The r e s u l t s  
o f  t h e s e  compar i sons  f o r  t h e  t i m e  of  o b s e r v a t i o n  from y e a r  1981 
till now are good enough f o r  t h e  m a i n t a i n i n g  o f  t h e  C o o r d i n a t e d  
U n i v e r s a l  Time S c a l e  UTC(YUZM1. Under such  c o n d i t i o n s  it i s  pos- 
s i b l e  t o  s t a r t  s e n d i n g  o u r  comparison r e s u l t s  t o  and i n t r o d u c e  
o u r  c o u n t r y  i n  Bureau I n t e r n a t i o n a l  d e  1' H e u r e .  
REFERENCES 
1. B. KovaEevie, "New ways ~f t i m e  and s t a n d a r d  f r equency  
d i s s e m i n a t i o n  o v e r  TV netwcl~.ks",  P roc .  9 t h  PTTI, pp. 277-287, 
November 1977. 
2. Z .  M. Markovie,  "De te rmina t i on  o f  t h e  Loran-C s i g n a l s  
p r o p a g a t i o n  t i m e  f rom t r a n s m i t t e r  t o  r e c e i v e r " ,  P r o c .  7 t h  
JUKEM, pp. 497-507, Oc tobe r  1976. 
3 .  G. M. R. Winkle r ,  "Pa th  d e l a y ,  i t s  v a r i a t i o n ,  and some 
i m p l i c a t i o n s  f o r  t h e  f i e l d  u s e  o f  p r e c i s e  f r equency  s t a n d a r d s " ,  
P roc .  IEEE, Vol. 60 ,  No. 5, pp.  522-529, May 1972.  
4 .  A. R. C h i ,  "Performance o f  Loran-C c h a i n s  r e l a t i v e  t o  UTC", 
P r o c .  6 t h  PTTI, pp. 263-299, November 1974. 
5. Conc lus ion  d e  l a  r e u n i o n  i n t e r i i n a i r e  d e  l a  Commission 
d ' e tude  7 Doc. 7/77-F, C C I R  Ceneve,  1984. 
6. BIH Annual Repor t s  f o r  1981,  1982,  1983. 
7. A. H. Morgan, " P r e c i s e  t i m e  s y n c h r o n i z a t i o n  o f  w i d e l y  
s e p a r a t e d  c l o c k s " ,  NBS T e c h n i c a l  Note 22 ,  J u l y  1959. 
UHlGlDIUl. P A G ~  $5. 
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The time and frequency comparisons via Loran-C and National TV Network in Yugoslavia

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