The results are given on the performance measurements, on the dependence on external temperature, and on external magnetic field of a hydrogen maser. It is compared with another hydrogen maser. Details of the transportation and installation of the maser are given. The hydrogen maser frequency is compared with cesium oscillators to derive long-term behavior

Busca, G.

Feil, D.

Nottarp, K.

Schlueter, W.

English

NASA Technical Reports Server

FIRST EXPERIENCES W I T H  THE H- 
Wolfgang Schl i l ter ,  Klemens Nottarp,  Dieter F e i l  
I n s t i t u t  f t i r  Angewandte Geodgsie (IfAG; A b t .  I1 DGFI), 
Frankfur t  am Main, 
Sonderforschungsbereich 78 S a t e l l i t e n g e o d b i e  (SFB 7 8 ) ,  
TU-Miinchen 
Federal  Republic of Germany 
Giovanni Busca 
ASULAE3, S.A., Neuchhtel 
Switzerland 
ABSTRACT 
The H - M a s e r  developed a t  ASULAB, S .  A.,  
Neuch2tel/Switzerland c a l l e d  EFOS 1 (Eta lon  - 
- Frequence Oscilloquartz)' - has been moved from 
Neuchdtel t o  t h e  S a t e l l i t e  Observation S t a t i o n  
Wettzel l ,  Federal  Republic of Germany. The 
r e s u l t s  are given on t h e  performance measure- 
ments,on t h e  dependence on external temperature 
and on external  magnetic f i e l d ,  which are der ived  
393 
https://ntrs.nasa.gov/search.jsp?R=19830027098 2020-03-21T01:14:24+00:00Z
a t  ASULAB by comparison with t h e  Hl- 
The experiences on t h e  t r a n s p o r t a t i o n  of 
t h e  H - M a s e r  i n  ope ra t ion  are presented  and 
t h e  i n s t a l l a t i o n  a t  Wet t ze l l  is descr ibed.  
The H - M a s e r - f  requency is compared wi th  t h e  
Caesium-oscillators of t h e  s t a t i o n  t o  de r ive  
t h e  long term behavior.  
INTRODUCTION 
The I n s t i t u t  f u r  Angewandte Geodasie a c t i n g  wi th in  and on behalf  
of t h e  Sonderforschungsbereich 78 (Sa te l l i t engeodas i e )  is ope- 
r a t i n g  t h e  s a t e l l i t e  observa t ion  s t a t i o n  Wet t ze l l  4 0 0  km east 
of F rankfu r t .  The s t a t i o n  Wet tze l l  i s  equipped wi th  a satel l i te  
l a s e r  ranging system, which w i l l  be extended t o  t r a c k  t h e  moon, 
and with sa te l l i t e  Doppler r ece ive r s .  A r ad io t e l e scope  f o r  geo- 
d e t i c  VLBI is  under cons t ruc t ion .  A t i m e  and frequency system 
is a v a i l a b l e  a t  t h e  s t a t i o n  t o  support  t h e  measurements w i th  t h e  
requi red  p r e c i s e  t i m e -  and frequency-informations [Sch lu te r  e t  
a l .  19811. To achieve h i g h e s t  accuracy i n  t he  VLBI-measurements 
a H - m a s e r  w i l l  be used. The S w i s s  l abo ra to ry  A S U L A B / O s c i l l o -  
qua r t z  o f f e r e d  t o  bu i ld  a H - m a s e r  f o r  t h e s e  purposes; a f t e r  
t h a t  they decided t o  s t a r t  t h e  development of a commercial 
maser. The EFOS 1 Maser (Eta lon  - - Frequence _I Osc i l loqua r t z )  has  
been-conceived i n  order  t o  ob ta in  optimum frequency s t a b i l i t y  
f o r  averaging t i m e s  between 100 s and 10 000 s for  t h e  requi re -  
ments i n  VLBI. Addi t iona l ly  t h e  design goa l s  a r e  high reliabi- 
l i t y ,  easy maintenance and cost e f f e c t i v e n e s s .  The design of t h e  
maser w a s  descr ibed  by Busca  i n  [Busca e t  a l . ,  19821, 
Af t e r  t h e  f a c t o r y  acceptance tes t  the  maser w a s  de l ive red  t o  
IfAG on Ju ly ,  23 1982. The maser w a s  t r anspor t ed  t o  Wet t ze l l  i n  
394 
f u l l  opera t ion ,  The t i m e  and frequency system a t  t s t a t i o n  i n  
Wet tze l l  c o n s i s t s  now of 3 Cs-clocksl 4 Rb-clocks, 1 H - m a s e r  
(EFOS 1 )  and 3 BVA-quartzcrystal osci l la tors .  The c o n s t e l l a t i o n  
of t h e  frequency genera tors  a t  Wet tze l l  does no t  allow t o  deter- 
mine t h e  maser frequency d r i f t  on t h e  basis of measurements over 
a pe r iod  of 3 month. This paper descr ibes  t h e  r e s u l t s  of 
acceptance t es t  performed a t  t h e  labora tory  of ASULAB using t h e i r  
maser H 1  and t h e  f i r s t  experiences a t  Wet t ze l l  s t a t i o n . '  
MASER PERFORMANCE DERIVED DURING THE ACCEPTANCE TEST AT ASULAB 
The acceptance test  of t h e  H - m a s e r  EFOS 1 has been performed i n  
t h e  per iod  from lgth t o  22nd J u l y  1982 a t  t h e  l abora to ry  of 
ASULAB. The test  procedure includes 
t h e  thermal s e n s i t i v i t y  
t h e  magnetic s e n s i t i v i t y  
t h e  frequency s t a b i l i t y  (Is, l O s ,  lOOs, 1000s) 
The condi t ions fo r  the  t es t  procedures w e r e  no t  t h e  best: A f e w  
hours before s t a r t i n g  t h e  acceptance test it was necessary t o  
rep lace  t h e  high vol tage  i o n  pumps power supply which r equ i r ed  
i n t e r r u p t i o n  of about 3 hours of t h e  masers normal opera t ion .  
Later during frequency s t a b i l i t y  test a main power f a i l u r e  
occurred (thunderstorm) which caused a complete i n t e r r u p t i o n  of 
t h e  re ference  maser H 1  and t h e  a i r  condi t ion ing  system. 
I t  is  clear best performance r e s u l t s  could no t  be achieved under 
such condi t ions.  I n  t h e  fol lowing t h e  tes t  r e s u l t s  are presented  
and also those r e s u l t s  are given which have been determined from 
measurements preceding t h e  acceptance test. 
395 
a )  thermal s e n s i t i v i t y  
The temperature w a s  changed stepwise (from 22.8 OC t o  18.8 OC) 
and t h e  corresponding frequency s h i f t  w a s  measured by comparison 
wi th  t h e  frequency of t h e  re ference  maser H I  , which w a s  kep t  a t  
a cons tan t  temperature.  The thermal S e n s i t i v i t y  w a s  ob ta ined  as 
Af/f =+1.7 x 10 - I 3  / degree Kelvin. 
A s  t h e  thermal test w e r e  performed only some hours after t h e  
high vol tage  power supp l i e s  replacement, t he  frequency of EFOS 1 
w a s  n o t  s t a b i l i z e d  enough and t h e  de t ec t ed  frequency change w a s  
no t  only caused by t h e  temperature change. These d a t a  do n o t  
correspond t o  t h e  measurements preceding t h e  acceptance test, 
made under s t a b l e  condi t ions  which g i v e  a thermal s e n s i t i v i t y  
of 
Af/f =-2 X 10 -I4 / degree Kelvin. 
b )  magnetic s e n s i t i v i t y  
Two t h i n  square coils w e r e  used t o  s imula te  v a r i a t i o n s  of t h e  
v e r t i c a l  components of t h e  ambient magnetic f i e l d .  The m a s e r  
frequency (EFOS 1 )  w a s  measured by comparison wi th  t h e  f r e -  
quency of t h e  undis turbed second maser H I  i n  t h e  fol lowing 
sequence. The ambient f i e l d  increment w a s  changed t w i c e  from 
+ 500 mGauss t o  - 500 mGauss without frequency measurement t o  
e l imina te  t h e  p o s s i b i l i t y  of t r a n s i e n t  h y s t e r e s i s  e f f e c t s .  Af t e r  
t h a t  5 c y c l e s o f  frequency measurements (100 s) have been per- 
formed by an ambient f i e l d  of + 500 inGauss resp .  - 500 mGauss 
and by a C-f ie ld  of 4 1 5  microGauss. The s e n s i t i v i t y  w a s  ob ta ined  
as 
396 
A f / f  = - 1. 1 0 - l ~  / Gauss 
c) S t a b i l i t y  T e s t  
Obviously under the given environmental condi t ions  t h e  fre- 
quency s t a b i l i t y  tes t  r e s u l t s  can no t  be as good as under stable 
condi t ions.  
The Allan Variances der ived under t h e  test  condi t ions  are given 
i n  table 1 compared t o  t h e  r e s u l t s  obtained under stable con- 
t 
in s 
1 
10 
100 
1000 
10000 
test  condi t ions  
-1 3 
-14 
-15 
-15 
4.1~10 
6.7~10 
7.7~10 
3.5~10 
number 
Df samples 
100 
100 
100 
63 
- 
stable condi t ions  
-13 
-14 
-15 
-15 
-15 
1.5~10 
1.9x10 
6.5~10 
1.7~10 
2.6~10 
number 
of samples 
100 
100 
100 
100 
18 
Table 1, frequency s t a b i l i t y  of EFOS 1 der ived  during the  
acceptance test  and der ived under stable condi t ions .  
d i t i o n s .  The measurement system bandwidth w a s  1 Hz for the  test 
condi t ions  and 6 Hz f o r  t h e  previous measurements. Consequently 
the  1 s and 10 s values  measured under stable condi t ions  have 
been normalised t o  1 Hz bandwidth. The frequency s t a b i l i t y  m e a -  
surement system has been described i n  [Busca e t  al., 19821. 
397 
TRANSPORTATION FROM ASULAB/NEUCHATEL TO WETTZELL 
The  H - m a s e r  w a s  t r anspor t ed  from Neuchatel t o  W e t t z e l l  i n  f u l l  
opera t ion  without  i n t e r r u p t i o n  ( f i g u r e  1 ) .  The t r a n s p o r t a t i o n  
took arround 2 4  hours with 10 hours d r i v i n g  on a d i s t a n c e  of  
about 650 km. 1 Stop  during n i g h t  t i m e  w a s  neccessary,  which 
w a s  used t o  charge t h e  batteries. 
INSTALLATION AT WETTZELL 
2 The maser was i n s t a l l e d  i n  a s m a l l  cellar room of  about 2.5  m , 
which is thermally i s o l a t e d  (cold the rmos ta t ) .  The maser w a s  p u t  
on a sand- f i l l ed  trough i n  which a g r a n i t  p l a t e  is "swimming" 
to  p r o t e c t  t h e  maser a g a i n s t  v i b r a t i o n s  t r a n s f e r e d  by t h e  
ground. The complete trough s tands  on a 2 c m  t h i c k  rubber p l a t e  
( f i g u r e  2 ) .  
A f t e r  t h e  t r a n s p o r t a t i o n  and t h e  i n s t a l l a t i o n  of t h e  maser, l o w  
c u r r e n t  degaussing w a s  needed. 
T h e  temperature i n  t h e  maser room climed up t o  27O C i n  J u l y  
and August mainly caused by t h e  ho t  summertime w e  had i n  Europe. 
Now t h e  temperature is  25O C. The room is isolated i n  such a 
manner t h a t  no d a i l y  temperature v a r i a t i o n s  w e r e  observed. 
MASER FREQUENCY CHANGE DUE TO TRANSPORTATION 
Before t h e  acceptance test  t h e  maser c a v i t y  w a s  tuned by sp in-  
exchange technique using t h e  maser H I  as a re ference .  The 
tuning w a s  done f o r  two d i f f e r e n t  va lues  of t h e  "C" f i e l d  
398 
(namely 8 3  LL Oersted and 15 1-1 Oers ted) .  The r e s u l t s  show t h a t  
t h e  c a v i t y  tun ing  s e t t i n g  w a s  independent of the "C'@ f ie ld  
wi th in  t h e  error of 1 x The nominal "CC"' f i e l d  value w a s  
set and t h e  syn thes i ze r  frequency w a s  ad jus ted  t o  t h e  value 
requi red  f o r  compensating t h e  evaluated W a l l  s h i f t  (- 2 x IO"") 
and t h e  second o r d e r  Doppler s h i f t  (- 4.3 x 10"'). The maser 
frequency was compared with a commercial Cs-standard and a rela- 
t i v e  frequency o f f - s e t  of 4.5 x 10 w a s  found. A f t e r  t h e  
i n s t a l l a t i o n  a t  Wet t ze l l  t h e  maser frequency w a s  compared wi th  
-12 t he  2 C e s i u m  s t anda rds  and a frequency o f f - s e t  of<l  x 10 
w a s  measured. This  imply t h a t  no major changes of t h e  m a s e r  
frequency occurred during t h e  t r anspor t a t ion .  
THREE MONTHS EXPERIENCES AT WETTZELL 
The m a s e r  frequency w a s  c o n t r o l l e d  a g a i n s t  t h e  f requencies  gene- 
rated by t h e  Cs-Standards over a per iod  of about 80 days. Phase 
measurements of the  5 MHz s i g n a l  of t h e  maser a g a i n s t  t h e  5 MHz 
output  of t h e  Cs-standards have been c a r r i e d  ou t  wi th  a HP-5370 
A counter .  To e l imina te  t h e  noise  of t h e  Cs-standards a mean 
value w a s  determinated by measuring of 10 x 100 000 samples of 
t he  t i m e  e lapsed between t h e  z e r o  p o i n t  c ross ings  of t h e  EFOS- 
frequency and Cs-standards-frequency. T h e  p r e c i s i o n  of t h e  mean 
phase measurement is  b e t t e r  than 0.1 ns .  The r e s u l t s  of t h e  
measurements are p l o t t e d  i n  f i g u r e  3. The measurements w e r e  per- 
formed aga ins t  t h e  two Cs-clocks (CS 7/Ser. N o .  131 and CS 8/ 
Ser. N o .  1 7 3 ) .  Curve I shows t h e  LORAN C comparisons of t h e  CS 7 
( d a i l y  phase va lue  c o r r e c t i o n  i s  taken i n t o  account) and g i v e s  
t h e  frequency r e l a t i o n  t o  UTC (USNO-MC). The second curve (11) 
shows t h e  comparison of t h e  t w o  used Cs-standards and curve I11 
and I V  g ive  t h e  maser-frequency compared t o  t h e  Cs-standards. 
399 
e f i r s t  change i n  the  s lope  appears i n  curve I, 11 and I 
happend a f t e r  t h e  i n s t a l l a t i o n  of a BVA-quartz o s c i l l a t o r  
t o  t h e  CS 7frequencygenera tor  (Mod. J u l ,  date = 45 1 9 9 ) .  A 
cor re l a t ion  of both events ,  t h e  BVA-installation and the  s lope  
change, can no t  be excluded. 
A s l i g h t  change occurs i n  the  curve I11 and I V  (on Modified J u l i a n  
da t e  = 45 21 4 ) .  T h e  change is  obviously caused by a change of 
t h e  maser frequency, poss ib ly  due t o  thermal e f f e c t s  ( f i g u r e  4 ) .  
The maser stopped i ts  opera t ion  on Mod. J u l .  date = 45 226 due 
to  a power in t e rup t ion  a t  the  s t a t i o n  over three hours. Poss ib ly  
t h e  vacuum became t o  low and the  maser stopped t h e  o s c i l l a t i o n .  
The co r rec t  vacuum w a s  r e s to red  a f t e r  2 days elapsed. The follow 
on frequency comparisons ind ica t e s  only a s m a l l  d i f f e rence  
aga ins t  the  frequency before  the  maser in t e r rup t ion  ( 2  x 10 e -1 3 )  
The last  change of frequency i n  f i g u r e  3 appears on t h e  curve I1 
and I V  on MJD = 45 255. T h e  CS 8-standard was moved from t h e  
temperature uncontrol led labora tory  room t o  a sepa ra t e ,  i s o l a t e d  
cellar (cold thermostat)  which has been f in i shed  a t  t h a t  t i m e .  
The measurements p lo t t ed  i n  f igu re  3 w e r e  f i t t e d  by a l i n e a r  
approximation. The s lope  w a s  determined f o r  t h e  curve 2 ,  3 and 
4 with in  < - +3ns/d and f o r  t h e  curve I within < - +10ns/d. The res& 
duals  are given i n  f igu re  5. The Allan Variance w a s  estimated as 
- 2.5 x EFOS-CS IO-1 (over 1 day) .  
I t  is obvious, t h a t  t h i s  value is  mainly inf luenced by t h e  
Cs-standard behavior.  The Allan Variance estimated from 'the 
CS 7 aga ins t  CS 8 measurements is 
400 
( 1  day) N 6 uCS 7/CS 8 
Assuming t h e  same q u a l i t y  for  both Cs-standards the  performance 
of t h e  Cs-oscillators could be estimated as 
(1 day) - 6 -r/zIx N 4 x 10 -1 3 %S < 
I t  has t o  be poin ted  ou t ,  t h a t  t h e  H - m a s e r  performance could n o t  
be estimated on the basis of the measurements over  a 3 month 
per iod by t h e  clock ensemble of Wettzel l .  From t h e  given r e s u l t s  
it could be stated, t h a t  t he  1 day behaviour of t h e  maser is 
better than f r o m  the Cs-standards. T o  have r e s u l t s  fo r  more than 
7; = 1 day, longer  undis turbed series of observa t ions  are needed. 
However no sys temat ic  frequency d r i f t  of t he  maser could be 
ascer ta ined ,  which w i l l  show up a s  a parabolic curve i n  t h e  
f i g u r e  3.  An upper l i m i t  of t h e  maser frequency d r i f t  from t h e  
p resen t  data can be roughly est imated as < 1 x 10’14/day. 
S tud ie s  on oscil lator performance have been started by e.g. 
comparing t h e  phase of the  maser frequency a g a i n s t  the Cs-clocks 
and the  BVA q u a r t z - o s c i l l a t o r s .  Current ly  no r e s u l t s  are avai- 
lable. To demonstrate t h a t  good r e s u l t s  w i l l  be expected t h e  
phases of a BVA osci l la tor  and of a Cs-oscillator a g a i n s t  EFOS 
are plot ted i n  f i g u r e  6. The smooth curve is the phase of t he  
BVA-crystal-oscillator. F u l l  scale of each record is  about 10 ns ,  
401 
References: 
[ l ]  Sch lu te r ,  W.; 
Nottarp,  K.: 
Appl icat ions of T i m e  and Fre- 
quency i n  Geodesy, IETE,  V o l  27, 
No.  10, 1981 
[ 2 ]  Busca, G.; Prel iminary Measurements on 
Addor, F. ; 
Hadorn, F.;  
EFOS 1 H - M a s e r ,  paper presented  
a t  t h e  36th annual Symposium on 
P r o s t ,  L.; Frequency Cont ro l ,  1 - 4 June  82, 
Brandenberger, H.; Ph i lade lphia ,  U.S.A. 
Thomann, P.; 
Johnson, L.: 
402 
0 
a, 
403 
4 04 
k 
a, 
tll z 
a, r: 
+, 
w 
0 
I 
-r 
a, 
k 
m 
k! 
405 
406 
I 
c .- 
E 
Q 
P I 
1 
! 
i 
i 
I 
I 
l 
i o n s  
Figure 6 - Phase - comparisons of 
the BVA-quartz oscillators 
against EFOS, CS-oscillator 
against EFOS 
407 
QUESTIONS AND ANSWERS 
DR. COATES: 
Any questions? 
MR. SAM WARD, Je t  Propulsion Laboratory 
I noticed t h a t  a f t e r  the power fa i lure,  the d r i f t  term changed. I s  there 
any explanation for that? 
MR. BUSCA: 
Af ter  the power fai lure, t h i s  i s  the d r i f t  we had before. This i s  a f ter  
only a ra te  o f  twenty nanoseconds per day. I have no explanation, maybe 
i t ' s  due t o  thermal effects because the .ce l l a r  room i s  not well insulated. 
MR. LAUREN J. RUEGER, JHUIAPL 
Do you have a means t o  f l u x  tune the masers a f te r  you are on the s ta t ion  
s i t e?  
MR. BUSCA: 
No. 
DR. COATES: 
Did everybody understand that? Your answer was 'ho", r i g h t ?  
MR. BUSCA: 
Yes. 
408 


First experiences with the H-maser EFOS 1

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