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Pulsar reception at 22 MHZ Dewdney, P. 1970

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PULSAR RECEPTION AT 22 MHZ  by  P. DEWDNEY B.A.Sc. i n E n g i n e e r i n g P h y s i c s , U n i v e r s i t y o f B.C.,  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF  MASTER OF APPLIED SCIENCE  i n the Department o f Electrical  We a c c e p t t h i s  Engineering  t h e s i s as conforming to the  required  standard  Research S u p e r v i s o r  i  Members o f the Committee  A c t i n g Head o f the Department.. Members o f the Department of E l e c t r i c a l  Engineering  THE UNIVERSITY OF BRITISH COLUMBIA  January, 1970  1968  In p r e s e n t i n g  this thesis  in p a r t i a l  an advanced degree at the U n i v e r s i t y the  Library  shall  permission  f o r s c h o l a r l y purposes may representatives.  be granted by  his  of  t h i s t h e s i s f o r f i n a n c i a l gain  Columbia,  f o r reference  the Head of my  It i s understood that  permission.  of  The U n i v e r s i t y o f B r i t i s h Vancouver 8, Canada  Date  British  requirements f o r I agree and  that  study.  f o r e x t e n s i v e copying o f t h i s t h e s i s  by  Department  of  make i t f r e e l y a v a i l a b l e  I f u r t h e r agree tha  written  f u l f i l m e n t o f the  Columbia  shall  not  Department  copying o r  or  publication  be allowed without  my  ABSTRACT  An (22 of  MHz) high  attempt  lower  i s made  than  they  to receive  have  g a l a c t i c background  receiver  used  optimizes  been  pulsar  received  signals before.  at a The  r a d i a t i o n i s the dominant  the ratio  of  signal  to sky  frequency  problem  one.  The  background  noise* The dispersed relation at  one  by  technique  intervening  i t i s possible  frequency  (150  MHz). The  time  with  eous  bandwidth  a  s t i l l  limit  to their  At  the time  at  22  — j o u l e s  MHz,  t h e known  signals  dispersion  of the pulsar  at another  tracks  the pulse  i s small  enough  signal  frequency  i n frequency  t o match  are  the  vs.  instan-  signal»  i t was  t o o weak  pulsar  the phase  i f i t i s known  then  which  of the  that  electrons.. Using  ( .22 M H z )  bandwidth  the property  to predict  receiver  Although are  uses  t o be  strength  found  received was  of observation  averaged over 2 p e r in o f c a p t u r e  that  pulsar on  such  obtained (August,  2600  a  from  system,  by m e a s u r i n g  cross-section  was  less  per unit  CP  an  1919  upper  i t s sensitivity.  1969) t h e s i g n a l  pulses,  i i  signals  than  strength 1,0  x  bandwidth.  10  TABLE  OF  CONTENTS  page 1 R  ABk)  TABLE  AC  l  Ol  r  1  >  i  e  4  e  <  *  «  »  C 0 iV 1 ilj JN7 P S  L I S T  OF  1  JPIJLSAIIS  e  «  «  «  e « o o « * « 6 « « e « « e « o e « * * e e «  e  6  0  *  c  «  e  *  *  J U S T I F I C A T I O N  3 . -•  S I G N A L - - T 0 ~N 0 1 S E THE"  ANTENXA  o  6 ©  THE  E.\1?ER I  T •  THE  EESUETS  «  *  8•  GONG LUS X ONS  ©  <  TZEFEr^ENCES  o  TLM  o  SYS  o  o  e  »  «  «  «  i  )  t  *  <  *  *  «  0  »  *  t  «  «  111  «  o  *  •  »  «  *  (  o  «  a  e  *  «  »  *  6  *  o  *  THE  *  «  «  »  «  »  c  >  t  J  »  «  9  e  *  e  *  1  o  E X P E R I M E N T . . . . .  ©  t  «  «  o  «  o  «  *  «  o  «  »  «  »  «  «  o  *  »  »  a  «  »  «  «  «  *  o  e  *  o  o  «  »  «  o  0  «  «  o  s  «  «  «  c  e  »  »  ©  »  *  *  o  «  «  »  o  «  o  o  »  *  iii  o  *  *  «  «  «  *  *  o  *  7 8  o  «  J  »  o  PROBLEM.  JViEN T  «  iv  OF  THE  5  »  I L L U S T R A T I O N S  2.  A- c  «  .11  «  «  <  *  «  #  «  «  >  e  «  o  o  «  c  e  «  «  «  «  «  o  «  «  «  «  «  «  «  «  «  o  «  #  o  *  «  *  «  «  «  *  e  «  *  e  *  »  o  11 13  IT  o  *  19  «  *  21  »  24  «  LIST  OF  ILLUSTRATIONS  page  Figure 1-1  The  Frequency  1-2  Pulsar  1-3  Pulsar  3-1  Sweep  5-1  System  5-2  Pulsar  Signal  6-1  Output  from  Signals  v s . Time Sweep R e c e i v ed  Spectra•••••••• Path  Followed  «  of the Pulsar  a t 408 .  e  by- t h e  «  .  «  »  .  Signal • •  MHz••»•«•«»•«»••••«» 6  w  .  «  Receiver  .  .  o  *  «  .  .  a t 22  .  o  «  «  o  .  .  »  .  t h e 22  3 5  o  MHz•»••••  9 14  Diagram........ R e c e i v e d on  2  t h e 1 5 0 MHz  M H z ^5 y 3 i ^ c i l i °  iv  0 , > , > o c c  S y s t e m «•••«••  16  **®**  18  c , ,  *  o o o , >  * * 0  ACKNOWLEDGEMENT •I wish to thank Professor F . K . Bowers for his guidance and encouragement  in carrying out this  research. Furthermore, I would l i k e to thank the  staff  of the Dominion Radio Astrophysical Observatory for their assistance and encouragement, the use of f a c i l i t i e s  and to  acknowledge  there*,  This research was conducted with the f i n a n c i a l assistance from a National Research Council bursary and from National Research Council grant A-3295 given to the Department of E l e c t r i c a l Engineering at the University of B r i t i s h Columbia.  v  1 1. PULSARS Since pulsars were discovered in 196B by hewish et a h at Cambridge, much work has been done to measure the properties of (1 J known pulsating sources, and to search for new ones. Pulsar: signals exhibit very unusual properties. At the source they arcpulses of radio frequency noise which are emitted over a very broad range of frequencies (from 40 MHz to a few GHz) The pulse repetition rate is exceedingly constant (to within at least 7 (2) one part in 10 per year) . Although i t has been presumed that the pulses are emitted simultaneously on a l l frequencies, i t has been found that pulsar signals observed on a low frequency are delayed with respect to those observed on a high frequency. Investigations of this phenomenon have shown, that there is dispersion caused by intervening electrons along the line of-sight to the pulsar. The measured dispersion accurately f i t s the relation c  41  =  -•£.-<•  7~ p where f is the received frequency c i s the velocity of light "  f  DT  d L  , --3 A f is the plasma frequency ( f - 8.98 x 10"" n^2 ) n is the electron density in the intervening medium dL is an increment of distance along the line of sight, or £1 1.2048 x 10~ f •s e where f is in MHz >n is in electrons-cm . e  4  3  =  3  f  °  -> n dL is known as the dispersion measure and is usually —3 quoted in parsec-cm ( 1 parsec = 3,26 l i g h t - years ). An i l l u s t r a t i o n of the shape of the frequency vs. time curve of observed pulsar signal is shown in Figure 1-1. In this model the pulse width is independent of frequency. There has been some evidence that the duration of the observed pulse is longer at low frequencies than at high ones. The effect is small but requires a more complicated theoretical explanation (4) of the dispersion . Among the pulsars there is quite a wide e  z  range of pulse repetition rates and pulse durations. The fastest repetition rate is about 30 per second; the slowest is about 1 every 4 seconds„ The pulse widths vary from 2 msec to 200 msec. The fastest repetition rates are usually accompanied by the longest pulse durations. Pulsar signals received at 408 MHz can be seen in Figure 1-2,  Figure 1-1 The pulsar signal sweep (not to scale), t is the pulse width (constant with frequency). P is the pulsar period. B. is the instanteous bandwidth. 1  The radio frequency spectra of the pulsar signals are very d i f f i c u l t to obtain because of the large, random variations in the intensity of the pulses. Some histograms of intensity distributions have been measured for the pulsar CP 1919. ( For the designation f pulsars see reference 4 ) A measured d i s t r i b u t i o n can be seen in reference 5. The d i s t r i b u t i o n function 0  3 decays exponentially at intensities  above the average  This type of d i s t r i b u t i o n has been observed at several  intensity,, frequencies  by Lovelace and Craft at Arecibo Ionospheric Observatory. Pulses outside a small frequency range do not seem to be correlated in intensity.  For instance,  at 430 MHz correlation was observed only in  a range of about 3 MHz for CP 1919.  —^JV^^ Figure. 1-2 Pulsar signals received at 408 MHz. The method of expressing pulsar signal intensity varies s l i g h t l y in the l i t e r a t u r e . The intensity w i l l be taken here to mean the t o t a l energy per average pulse s t r i k i n g a unit capture cross-section per unit bandwidth. The intensities quoted in the l i t e r a t u r e have been standardized to this form. Where necessary pulse widths for this standardization have been taken from reference 4. Some spectra are plotted in Figure 1-3 for CP 1919. The wide range of intensities is due partly to the different averaging techniques used by the various observers, and partly due to the large, long-terra variations in pulsar signal strength. Each spectrum in Figure.1-3 is denoted by a l e t t e r and a number. The l e t t e r stands for the observatory where the spectrum was measured. The number is the number of pulse periods used to obtain the average. Spectra which have been drawn from selected large pulses or groups of such pulses are noted. Inevitably, there w i l l be some selection effect because weak pulses w i l l be l o s t in background noise. Note that although there are shifts of overall l e v e l , . t h e shapes of the spectra measured by different observatories are similar,, (with the exception of one point on the Parkes spectrum ). Periods quoted in the l i t e r a t u r e are usually referred to the earth-sun barycentre. Owing to the motion of an earth-  —  4  bound  observer  with  doppler-shifted. this axial  effect  respect  The  but there  rotation.  to t h i s  earth's i s also  point,  orbital a daily  motion  the period  will  contributes  variation  due  be  most  to i t s  of  5  Pulsar  Signal  Intensity  (joules-m~ -Hz ) x 2  10 MHz  - 1  10"  100  MHz Figure  1 1-3  GHz  6  Note MHz  1:  The  Parkes  spectrum  represents  identification  of  reported  very  d i f f i c u l t .  -26  -2  was  mined  to  energy  be  .06  pulses  lower  than  2 s The  MHz,  and  reports  a  10  may  have  which  4096  of  .85  been  than  spectrum  -Hz  i s a  1.3  times  .3  x  the  average  . Because  w'as  deter--  from  this  many  of  average,  t h e lowi t may  be  pulses.  6144  a t 430  i s a variation  to  p u l s e a v e r a g e . A t 85 -•-'6 -2 ~] 10 " joules-m -Hz  -1  these  average  5000  However,  excluded  includes  pulse  there  less  joules-m  Arecibo  that  data  x  one  Note  the  t o be  pulses  a  pulse  MHz.At  i n 6  average 111.5  equal  MHz  at  111.5  Arecibo  subdivisions of  the average.Similarly, i n 4  s u b d i v i s i o n s a t 4 3 0 MHz t h e r a n g e w a s f r o m (5) average. A t 4 0 MHz t h r e e o b s e r v a t i o n s o f  .4  to  1,6  4096,  7>1,  equal  times  the  and  3940  pulses  were averaged. T h e r a n g e w a s f r o m .2 t o 1.6 t i m e s this (private letter) . . . , ... j , average. Because these i n t e n s i t i e s were reported n  r  as  peak  the  flux,  mean  pulse  Note  3 s The  8100  pulses.  4t  At  factor  1/  spectrum  Included  2  was  introducted to  determine  i s an  i n this  average spectrum  over  approximately  a t 82  MHz  i s a  raeasureinenx. 22  MHz  noise  level  has  as  upper  limit  an  of  height«  Jodrell (15)  Camondge Note  a  x  the  been  level  of  indicated  three  standard  f o r a  5000  f o r comparison  with  and  deviations of 8100  the other  pulse  spectra.  the  average  7 2.  JUSTIFICATION OF THE  EXPERIMENT  There are no observations of any of the pulsar spectra at frequencies  less than 40 MHz, and the work done at frequencies (3) less than 80 MHz is very l i m i t e d . Although the data are very incomplete, I O '  2  0  i t appears that the pulsar intensity may be less than  joules-m" -Hz™ 2  1  at  22  MHz.(see Figure 1-3). The a v a i l a b i l i t y  of a large antenna at this frequency at the Dominion Radio Astrophysical Observatory near Penticton, B . C . makes detection in this flux density range feasible. The physical area of this antenna 2 i s 23,693 ra . It i s comparable to the collecting area of Arecibo Ionospheric Observatory's c i r c u l a r dish at this frequency. Even an upper l i m i t in this s e n s i t i v i t y range would be s u f f i c i e n t l y low to be of use in determining the slope of the spectra of pulsar signals at low frequencies, A spectral cistoff at low frequencies would be useful in r e s t r i c t i n g theories of the origin of pulsar signals. Also, since the dispersion is proportional to the inverse square of the frequency, a measurement of the delay from frequencies above 100 MHz would give a very accurate dispersion measure. T h i r d l y , as indicated in chapter 1, there i s some evidence that the pulse gets systematically wider as the frequency decreases. Previously, i t had been thought that the pulse width vras independent of frequency. Detection - of-the pulsar signals at 2 2 MHz would be a sensitive measure of this trend* These considerations provide the basis of j u s t i f i c a t i o n of the experiment described herein.  8  3.  At sky  frequencies  sky  part  temperature.  temperature  PROBLEM  the background  The " c o l d e s t "  of brightness  brightness  2 2 MHz  near  i s considerable.  degrees  S I G N A L - T 0 - X 0 1 S E  rises  noise  from t h e 40,000  of t h e sky i s about  In the plane  of the Galaxy the  as 2 8 0 , 0 0 0  as high  degree's.  (7) This  r a d i a t i o n i s p r i m a r i l y nonthermal  ground  brightness  55.,000  appears  of  explained  not accurately  has  a  that  known.  t h e power  steeper  slope  Therefore, a high  taneous  bandwidth  than  enough  noise  level  hand,  the pulsar  width  than  1,  index  f o r pulsars  bandwidth  time  a  pulsar.  The  t h e paramount ratio.  of a  time  period,  signals  order  the centre  i tfollows  problem i s  signal  increases  level.  On  the  through  increasing  and that  where  6f i s t h e sweep 1J\  A  t h e optimum  v s , time  curve  power  i bandwidth. of the receiver  bandwidth  band-  band-  of the receiver can  the signal-to-noise  i s the instantnaeous  large  t h e maximum i n t e g r a t i o n  frequency  the frequency  bandwidth  other  i s the instantaneous  to gain  the  i n Appendix  factor  fixed  a  than  the available  fsP B.  an optimum  instan-  t o more  •J over  slope  1 - 3 f o r comparison.  receiver  I t i s shown  i s overwhelming,  Now,in  The  A typical  t o sweep  one, thereby  pulsar  radiation  i s 1 0 k H z a t 2 2 MHz ( s e e  the signal  period.  spectrum, i n Figure  of the pulsar  per pulsar  result i s that  by a  power  signals  longer  small  f o rreceiving  so t h a t  increased  a  availablei t  of the sky background  the bandwidth  takes  effect  per pulsar  t h e data  signal-to-noise  increasing  of the pulsar.  swept  from  the pulsar  bandwidth  without  the f i r s t  the spectral  However,  of pulsar  through  integration  time  1 9 1 9 i s about  radiation i s indicated  instantaneous  width  o f CP  spectrum  3 - 1 ) . Increasing  Figure  that  back-  i n the v i c i n i t y  a t low frequencies  getting  be  i n chapter  t h e background  the  The  degrees.  As is  temperature  i n origin.  of tne pulsar  of the  ratio i s  9 Because  of the l i k e l i h o o d  0  f  g a  i  fluctuations i n the receiver  n  a c o m p a r i s o n s o u r c e i s u s e d i n t h e same way as i n a D i c k e r e c e i v e r . The  c o m p a r i s o n i s t h e b a c k g r o u n d n o i s e . The r e c e i v e r b a n d w i d t h  follows the pulsar f o r one-half the  sweep f o r t h e o t h e r  half.  o f t h e p u l s a r p e r i o d , and r e p e a t s  Of c o u r s e ,  r e c e i v e r sees o n l y background n o i s e  t h e second t i m e t h e  (see F i g u r e 3-1). A l l t h e  r e c e i v e r p a r a m e t e r s a r e t h e same f o r t h e f i r s t h a l f . The b a c k g r o u n d n o i s e r e c e i v e r takes  h a l f as f o r t h e second  i s a l s o t h e same f o r b o t h sweeps. The  t h e d i f f e r e n c e between t h e o u t p u t s o f two  sweeps w h i c h i s p r o p o r t i o n a l t o t h e p u l s a r s i g n a l  successive  strength.  Sweep  Bandwidth  F i g u r e 3-1 A r r o w s i n d i c a t e t h e p a t h f o l l o w e d by t h e r e c e i v e r when i t i s i n p h a s e w i t h t h e p u l s a r s i g n a l . F o r CP1919 t h e sweep b a n d w i d t h i s 70.7 kHz a n d the. i n s t a n t a n e o u s b a n d w i d t h ( B ^ i s 4.2 k H z . CP1919's h e l i o c e n t r i c p e r i o d i s 1.3373011 s e c o n d s . One bandwidth phases  important  a s s u m p t i o n t h a t has been made i s t h a t t h e  sweep i s i n p h a s e w i t h t h e p u l s a r . I f a s e a r c h  i s required, then the gains  of the  i n s i g n a l - t o - n o i s e r a t i o made  by a s w e e p i n g b a n d w i d t h a r e n u l l i f i e d .  However, any i n f o r m a t i o n  about t h e phase can r e s u l t i n a h i g h e r  p r o b a b i l i t y of detection  w i t h a sweeping bandwidth. I f o b s e r v a t i o n s  a r e made  simultaneously  10  on  a  high  signal to  a t 2 2 MHz  give  and  frequency  tional again  adding  amplitude  dependenc trains  Therefore, than the  can  be  It  was  ference  accuracy  Arecibo work  However,  f o rabout  time  that  discussed  time  30 s e c o n d s .  by a f u r t h e r averaging t o concentrate that  i n trains  at night.  a t 2 2 MHz.  Ionospheric  were  at higher  frequencies.  strong  longer  frequencies  The  integration  longer  integration  on t h e p u l s a r being  A t 2 2 MHz about  made  and t h e r e  seen  CP 1 9 1 9 .  CP 1919  man-made  inter-  9 : 3 0 p.m.  and  d i s p e r s i o n measure.  t o p r e d i c t t h e phase  CP 1 9 1 9 h a s b e e n  Observatory,  length  of the records.  t o between  i n order  they  average.  At low  Of c o u r s e ,  CP 1 9 1 9 h a s a n a c c u r a t e l y known  i s required  that  w hose  on t h e  be g u e s s e d .  by  r  1 9 1 9 a t 8 5 MHz  efforts  observations  observations  be i n c r e a s e d  i s active.  can only  i n which  of the other  to i n t e g r a t e f o riinies  a pulsar  the meridian  Also,  bo  propor-  i tappears  one minute  signals  done  could  to last  restricts  This  pulsar  of detection  seem  of year  a.m.  will  independent  F o r CP  decided  7:00  problem  the frequency.  transiting  frequency  p u l s a t i n g phenomenon  to the next.  f o r CP 1919 was  t h e time  This  independent, but odcur (9)  integration  was  c a n be i n t e g r a t e d  at a high  upon  obtained  of the pulsar  difference i s directly  i s s t a t i s t i c a l l y  period  t h e average  used  1-1  t h e epoch  steadily  i ti s disadvantageous  optimum  time  a  the probability  one p u l s e  pulse  The time  were  not s t a t i s t i c a l l y  is  t h e phase  6.  the pulsars  amplitudes,  At  a t 2 2 MHz.  i n chapter  pulse  are  d i f f e r e n c e between  t o t h e d i s p e r s i o n measure.  If one  a s a t 2 2 MHz,  c a n be p r e d i c t e d , l i q u a t i o n  t h e time  t h e epoch  as w e l l  of the  a t 4 0 MHz  has been  by  considerable  11  4.  The T-shaped wave  antenna array  dipoles  above  a  used  degrees  steering  MHz.  Phasing arm by  methods.  a n d 2.1  degrees  of the individual switching  method  was  of  ( a p p r o x i m a t e l y one hour)  scans  a  few degrees  to  be made  of  the Galaxy,  from  The  the total  Observations  of  scintillations of  each  for  the  and  area  units ( 1 (12)  polarized.  unit  The n o i s e  The r e s u l t i n g  compared  sensitivity  of  factor  polarizationo  two because  2  the antenna  several A had  i n the plane subtracted  o f C a s s . Ac,  shown  ionospheric  that  of a  factor  good f l u x (11)  records was  .  den~  Comparison  done i n  temperature* T h i s method t h e ohmic l o s s factor A  a t 2 2 MHz =  1Q~  2 6  with  a  has a  flux  watts-ra~ -Hz"" 2  temperature  area  i s receptive  1  due t o . t h i s  standard  the antenna  p e r degree. The o v e r a l l e f f e c t i v e A ---~ -|- = 3 7 6 m ° e o 2  at the  of the order  Cass.  by  broadness  be  f o r t h e antenna  flux  was  must  scintillating  substituted  to the amplifier  units  i s a  from  done  of Cass.  c o m p l i c a t e d by  i t has been  cables i n the antenna.  degrees.  There  even  to the  side  the effect  fluctuations  However,  was  i s located  including  the input  flux  A  overall effective-  i s randomly  7000  each  the Galaxy  further  caused  flux  at  i n the  the antenna  Owing  of noise  o f 51,400  o f 14  i n R i g h t Ascension,  Cass.  from  A were  source  beamiwidth  Ascension.  to get absolute values  the feed  density  one  which  a noise/  case  gives  7.3  Cass,  A.  on  to isolate  c a n be d e t e r m i n e d  against  at  radiation  two i n t h e r e c o r d .  sities  baseline.  i n order  and i t s c e n t r e  of the antenna  Casseopeia  i n Declination  to provide a  mounted  of dipoles  to point  bright  source  and  f u l l -  i n Declination  rows  but not i n Right  of the sensitivity  The f i r s t  o f 24.0  MHz  l e n g t h s o f c a b l e as d e l a y s p r o v i d e s  well-known, t h e beam  direction  I t has a half-power  i n Declination,  Calibration  arm o f t h e 22  I t i s an a r r a y  i n the East-West  i n Right Ascension  North-South  two  of the North-South  s c r e e n , , T h e a r m i s 4X w i d e ,  i s 22.25  zenith.  ANTENNA  at D.R.A.O.^^  polarized  reflecting  frequency  the  consists  THE  source  and found  i s then i s then to  )  only  t o be  The  aperture efficiency The  region  o t h e r method  near  brightness the  the  value  at  i s to  North  Pole  temperature  brightness 38  of  MHz^uling  a  where  i s the at  * at Because shape  the (as  n  be  The  in this  as  f  ohmic  ratio  background equally. in  the  the  index  The  value  obtained from  of  average  2.50^^.  of  the  background  temperature  of  the  background  measured Loss  i s not be  to  =  factor  so  an  broad  at  =  cable  l i t t l e  the  gives to  background  of  the  beam  constant ohmic  loss  preamplifier  3.1#  -  affect of  the  i s added  Efficiency  the  attenuate the  noise  the  the  Overall Aperature Ohmic L o s s F a c t o r  losses  the  degrees.  1180 38,000  not  of  source  input  1180  does  extra  that  extended  measurement  be  Factor  Factor  i s independent  f i l l i n g  factor,  because,  i n this  case,  antenna  the  output  can of of  antenna  the  one.  only  the  shape  same  half  signal  n o i s e power  independent has  absorb  however,  signal the  noise  of  the  affect  the  the power  as  antenna  antenna  and  the  cabling  but  this  noise system  ratio  mentioned i s more  beam.  less  A  comes  geometrical area  power.But,  from of  does  - „ *  signal-to-  noise  by  _ ~  antenna.  the  of  the  temperature  s i g n i f i c a n t l y . S i n c e most  Very  MHz.  an  2.50  antenna  beam  The  larger  was  22  has  l  temperature  loss  sky,  at  region  The  J  b2  temperature), this  case  This  sky.  .  of  F i l l i n g  noise  0  the  noise  MHz  f„  considered to  Ohmic  The  22  l»7f«.  background  degrees  spectral  brightness  e  output  long  can  factor,,  ^  s  the  =  f ^.  frequency  brightness  was  at  brightness  frequency  at  chosen.  38,000  T, , A  ef f e c t i v e area p hy s i c a 1 a r e a  look was  temperature  i.e.  sky  i s then  The  signal  or  above, less  smaller than  of  the  13  5. A  block  diagram  22  MHz  antenna  an  amplifier with  MHz.It MHz, It  i s mixed  and i s  is  fed  of  the  connected a  3  with  into  db a  an  to  swept  I,F.  a m p l i f i e d . The  is  system a  i s  of  local  is  discharged  chart  recorder.  MHz  a  signal  oscillator  was  i n the  calibrated  provides  and  can  be  a  accurate  frequency  checked  CP  at  22  1919  the  seconds.  at  W.W.V.B. 6 0  MHz.  the  In  deviates  counter  various  a  42  Hz  from  of  voltage  output  of  Therefore, the  oscillator  to  be  a  of  the  Hewlett-Packard  for  synthesizer  was  maximum  (  sky  plusrreference is  done  of  a  more of  by  switching  than  400  Hz.  with  (signal  plus  i s done  integrator.  The  slightly  of  of  the  must sky  that  a  a  1  can  was  this  timing control well  as  used  the  a  to  local  a  good  half  a  pulsar  at  22.25  used  to  oscillator  of  pulsar. i s  approximaperiod  MHz.  This  bandwidth  control  synthesizer  as  the  s t i l l  a  the local  frequency  I t was  described  be  in  subtracted  background). the  output  jjulsar  measured, only  one  chapter  from  This into  the  tenth  3,  the  source  subtraction opposite  half-period.  inputs  Since a l l  the  pulsar  repetition  rate,  there  is  spurious  timing  signal  build  up  the  o f f - p e r i o d s of  the  phase  so  the  period  that  during  a  crystal  of  be  of  MHz  on  pulsar.  method  switching  twice  the  displayed  instantaneous  deviation  a m p l i f i e r each at  ramp  detected  detector  to  non-linearity  This  the  background)  alternately  possibility  that  to  kHz  f i l t e r .  sweep*  linearity  4.2  32.950  The  frequency  output  frequency  The  bandwidth  differential  lapped  system.  accordance  reference  no  the  instaneous In  a  the  is  pulsar,- as  the  at  an. i n t e g r a t o r  down  delay  corresponding  of  1919.  The  22.250  phase  c a r r i e r . The  the  along  a  output  dividing  at  at  into  crystal  into  sweep i s l i n e a r  i s only a s m a l l f r a c t i o n CP  The  that the  so  pulsar  about  into  The  fed  detected.  then  kHz  delay*  points  sweep  fed  a  5-1.  i s  centred  then  s y n t h e s i z e r . 1'he  digital  Figure  centred  then  and  i s done' by  frequency  Fortunately, tion  30  timing  with  kHz  i s then  various triggering l e v e l s  17-position, trigger  every  The  300  p r e a m p l i f i e r and 10 7  in  oscillator  made f r o m f i e l d - e f f e c t t r a n s i s t o r s , which  shown  preamplifier which  bandpass  f u r t h e r amplified, at  output  SYSTEM  THE  can  detector of  are  in  over-  possible transients,  16.6 db Coupler  22 MHz Preamp.  Cable  22 MHz R.F. Amp.  Mixer  10.7MHz I.F. Preamp.  Crystal Filter B.W.= 4kHz.  10.7MHz Amp.  Frequency Counter  Noise Generator  HighPass Amp.  Frequency Synthesi zer  Switch  Detector  Phase Detector  Timing Control  Integrator Reset Timer  integrator  Master Clock Chart iecorder  V  Sweep  25.6 m P a r a b o l o i d w i t h 151 MHz f e e d  150 Miiz Preamp. C a b l e  Time Oscillator  Receiver  Synchronous Averager  Figure 5 - i  Chart Recorder  15  System  Diagram:  paths,,  Thin  Signals  from  frequency  Thick  lines  lines  represent  Timing  represent paths  R. F„  paths  of control  and main  signal  signals.  Controlt o *  Synthesizer V o 1 1 a g e Ramp c o n t r o 1 s output frequency  F r e qu en cy  C o un t e r L e a d i n g edge t r i g g e r s c c u a t e r . P h a s e c a n be adjusted i n steps of 40 m s e c .  Phase  Detector S o l i d square wave c o n t r o l s one h a l f . o f p h a s e detector; do11ea square wave, t h e o t h e r half.  Svnchronous  Averacer L e a d i n g edge t r i g g e r s sweep o f F a b r i t e k Averager. The phase o f t h i s s i g n a l can a l s o bo a d j u s t e d ,  Noise  Generator  Switch T h i s s i g n a I a dA s n o i se to t h e i n p u t of t h e sy stein e v e r y h a. I f p u i s a r p e r i o d f o: c a l i br a t i on.  •*  On e P u i s a r P e r i o d 5-1  there  i s no The  a. n o i s e sweep  signal  sensitivity  on  and  150  MHz  D.lt.A.O.  A  detected  output  that  typical is  dipole  one  output  triggered  phase  from  of the local  adjusted  antenna feed  relative  synchronously  overall  i s t h e 26.5  i s used a  o f t h e 236  from  The  c a l i b r a t e d by  this  with  system  the timing  m  Sinythe  minute  be  i s one  sweep  trigger  averager  pulsar  i n Figure  i n t h e 22 i n t h e 22  MHz MHz  average  period, 5-2.  system  MHz  system,  sweep The  can  -C=»  Sign a1  A  The  system.  Period-  Figure 5-2 f r o m t h e 150  The arranged  pulse.  Pulsar  at  preamplifier.  1 10  the  w i l l  paraboliod.located  i s shown  control  oscillator to this  a  channels  Pulsar  typical  with  sensitivity  256-channel- s i g n a l  One  A  switching  7,  i s fed into  sweep  detector..  c a n be  the preamplifier  half-periods.  i n chapter  The  out of the phase  of the system  o f f into  on. a l t e r n a t e  discussed  so  coming  bo  17  6, As be  i n phase  benefit a  was  If  with  observations  then  out i n chapter  equation  f  2  f  1  For  CP  easily  a r e made  1 c a n be  1 5 1 . 5 MHz  =  22.250 t =  109.91  of the local  to cover  a range  searching  a l l possible  explained  with  a fixed Figure  during when the 30  method phases phase.  t o be  eprch  a t 22  strongest  indicates  near  on t h e two  at  MHz,  literature  150  Mlizo  frequencies  give  The r e q u i r e d  phase  second  change  was  of about was u s e d  on t e n o c c a s i o n s  scanned  can  100 msec as a  and spending Earlier  on each  method  The  of the  compromise  between  the entire  observing  observations  h a s no a d v a n t a g e  this  a  durixig t h e  before,  were  were  made  scanned, b u t , over  observing  bandwidth. 6-1  shows  of the output average.  a typical  piece  The s t r a i g h t reset just  of chart  lines  record  occur  30 s e c o n d s ) . this  point  section contains  section  5-1) s l i g h t l y  (every before  The f i r s t  and t h e second  see Figure  sweep  way  phases  the observations.  value  i n this  a l l of the possible  t h e i n t e g r a t o r was  noise (  This  at the predicted which  made  oscillator  phase.  as  f u l l  f l  seconds.  were  predicted  during  t  The  must  be c a l c u l a t e d .  observations  time  t h e phase  simultaneously  f 2 "  to get the  t o g e t t h e pvO.se  151.5 MHz,  integrated to  sweep  MHz.  Observations phase  was  signals are likely  =  1919  i n order  I t i s possible  chosen  t  where  signal  3, t h e b a n d w i d t h  and use i tto predict  frequency  the pulsar  EXPERIMENT  the pulsar  frequency  high  that  pointed  of the system*  high  The  THE  contains  l a r g e r than  a  made  at the points Therefore,  represents only  simulated  a  background pulsar  one s t a n d a r d  signal  deviation.  1J. QO  .Figure  6-1  O u t p u t f r o m the 2 2 MHz p u l s a r system. T h e u p p e r n o i s e ; the l o w e r one i s b a c k g r o u n d n o i s e p l u s a signal.  trace i s background simulated pulsar  19  7. The  minimum  determined noise  by  to  background +  10,000  with  the  be  RESULTS  detectable brightness temperature background  temperature.  measured  THE  The  200  sky  noise  temperature  temperature  degrees,above  ambient  brightness temperature  degrees  which  this  i n the  the  to  1 3  be  receiver  receiver  55,000  1919,^  the  the  temperature.  contributes  r e g i o n ' n e a r CP  i s transmitted  of  and  will  '  The  preamplifier  was  The decrees efficiency  i s  3.1$.  Therefore,  T  = G'T. +  S  = where  r  (l-e)T  A 2186  +. 1'  o  R  degrees  i \ i s the o v e r a l l system temperature s T., i s t h e a n t e h r i a temperature A T i s ambient temperature q  T  i s the  R  The  standard  receiver  deviation  of  For  a  B  i s the  I.F.  x  i s the  integration  single  time,  and  of  1919  CP  point  tiie  on  the  bandwidth  ) i s 4.0  of  figure  13.8  kHz.  approximately calculations made 6.9 is p:«7  10$ but  interference. flux  40 x  pulsar  units  msec., 10  ^  per  then  intensity).  the  record  from  also  there as  than 120  the be  the  i s a  the  30  second  integration  instantaneous  bandwidth  «  the  measured  samples limits  and  (  ).  of  attributed  sensitivity  standard "-Hz  system  degrees  lower  degree  joules-m  of  12.6  Since  the  i s  time °  i s within could  output  Then,  =  ( taken  .  T  ( chosen  i s somewhat  degrees  noise  bandwidth  a This  the  = 2  •a  where  temperature  the  pulse  deviation expressed  The  standard  d i f f e rence  accuracy to of  of  the  the  i n the  antenna of  CP  noise  same  of  the  low-level,  length of  deviation  mani s  1919 i s  units  as  20  As longer time If  explained  periods  that  , as  i n chapter  than  the source  in a typical  30  3 the i n t e g r a t i o n  seconds  by  averaging  i s i n the antenna  beam  night's  observations,  a =  degrees.  c a n be  done f o r  the records.  The  i s about  hour.  120  points  one are  then  This  standard  signal  1.2  d e v i a t i o n of noise  intensity  of  .34x10"^  corresponds  joules-m  ^_Hz"  toaa .  pulsar  total  used,  23 APPENDIX The  optimura  fixed  can  be d e d u c e d a s  The  receiver  Tj,  time  that  t h ereceiver  <  v  B The  maximized,,  Since  p e ru n i t  TQ  output  (assuming voltage  two i n t e g r a t i o n s ,  constants o f  bandwidth  bandwidth  ratio  of t h e pulsar  i sobtained  when  v t h etwo p r o c e s s e s T  a n d V Q a r eassumed  andv^ a r e independent,  v a r ^  t o be G a u s s i a n ,  var  v,, =  var  v, =  then  "2(p£B+nB;  var(v^)  and  time  these  (neglecting  var $> = var<v^> + If  between  power  of t h e receiver  signal-to-noise  var is  power  i st h eb a n d w i d t h  The  noise  proportionality)  i st h ei n s t a n t a n e o u s  best  signals  0  ~ nB  signal  over  lawdetector).  > = ^ l V ^ T  YQ  6B  pulsar  plus  power  the noise  = p 6 B + nB  i sp u l s a r  power  the difference  6B<B  p  signal  has a square  the receiver, v, is  where  pulsar  and integrates  i.e. If  f o r receiving  followst  integrates  over  of  bandwidth  v a r v„ =  n B 2  If  v a r / ? , ) « v a r v.  p « n  ' But  T,  --^ .  T is  h e  0  sweep  n  long  If  6B>B,  as  B should  be  as small  as  possible  6B<B.  v±  then  Therefore,  =(p  v  o r B should  Taking  bandwidth  (^ )  2  var  B<5B.  T. 1  rate  df/dt  S i n c e <v) ~ i s p " 6 B t h e b a n d w i d t h as  -  period  var<V>~ 2  1  a n d T„ = T  B  pulsar  t h ep u l s a r  Substituting  2HT7"  dfTdt"  1  where d f / d t i s t  n B  =  into  must  account  b e B — 5B«  + n) B  n  -j  b e made  T,  as large  t h eabove  result,  as possible t h eoptimum  as long  as  receiver  24 REFERENCES 1. H e w i s h ,  Bell,  Pilkington, Scott, Collins,  Rapidly Pulsating 1968,  "Observations of a  Radio S o u r c e " , N a t u r e , V o l . 217, Feb. 24,  p. 709.  2. D a v i e s , S m i t h , H u n t , " C h a n g i n g  Periodicities  i n the Pulsars",  N a t u r e , V o l . 2 2 1 , J a n . 4, 1969, ;;p„ 2 7 . 3. D r a k e , Gunderraann, J a n c e y , C o m a e l l a , Z e i s s i g , C r a f t , "The R a p i d l y V a r r y i n g Eadio Source i n V u l p e c u l a " , S c i e n c e , V o l . 160, May 3, 1 9 6 8 , p. 503. . 4. T a y l o r , J . H . , " C a t a l o g u e o f 37 P u l s a r s " , A s t r o p h y s i c a l  Letters,  Vol.::3, 1969, p. 205. 5. L o v e l a c e , C r a f t ,  " I n t e n s i t y V a r i a t i o n s o f t h e P u l s a r CP 1919",  N a t u r e , V o l . 2 2 0 , Nov. 3 0 , 1 9 6 8 , p . 8 7 5 . 6. B r i d l e , A.H., "The S p e c t r u m  o f t h e Radio Background  Between  13 and 404 MHz", M o n t h l y N o t i c e s o f t h e R.A.S.,Vol» 136, 1967,  p. 2 1 9 .  7. K r a u s , J o h n D., " R a d i o A s t r o n o m y " ,  M c G r a w - H i l l , 1966, p.236,  p. 3 1 0 . 8. W i l l i a m s , K e n d e r d i n e , B a l d w i n , "A S u r v e y o f R a d i o S o u r c e s and Background  R a d i a t i o n a t 38 M H z " , M e m o i r s R o y a l A s t r o n o m i c a l  S o c i e t y , V o l . 7 0 , 1 9 6 6 , p . 53. 9» R o b i n s o n , C o o p e r , G a r d i n e r , W i e l e b i n s k i , L a n d e c k e r ,  "Measure-  ments o f t h e P u l s e d R a d i o S o u r c e CP 1919 b e t w e e n 85 and 2700 MHz", N a t u r e , V o l . 2 1 8 , J u n e 2 2 , 1968, p , 1 1 4 3 . 10. C o s t a i n , L a c e y , R o g e r , I.E.E.E. No.  "A L a r g e 22 MHz A r r a y f o r R a d i o  T r a n s a c t i o n s on A n t e n n a s  2, M a r c h ,  Astronomy",  and P r o p a g a t i o n , V o l . AP-17,  1969, p. 162.  11. P u r t o n , C.R., "The S p e c t r a o f R a d i o S o u r c e s and B a c k g r o u n d R a d i a t i o n " y t D o c t o r a l T h e s i s , U n i v e r s i t y of Cambridge, J u n e , 1966. 12. R o g e r , C o s t a i n , L a c e y , " S p e c t r a l F l u x D e n s i t i e s o f R a d i o S o u r c e s a t 22,25 MHz", A s t r o p h y s i c a l J o u r n a l , V o l . 174, No,  3, A p r i l  1 9 6 9 , p. 366.  2 5 13.  Gait, of  Costain, t h e Royal  Sec,  3,  "Low-frequency Society  o f Canada, F o u r t h  R.,"Statistical  N a t u r e , V o l . 219, S e p t . ,  of  Transactions  S e r i e s , V o l . 3,  1965.  14. W i e l e b i n s k i ,  15. L y n e ,  Radio A s t r o n o m y " ,  Properties  1968, p .  R i c k e t t , "Measurements  of P u l s a r  CP  1135.  of the Pulse  Shape and  t h e P u l s a t i n g R a d i o S o u r c e s " , N a t u r e , V o l . 218,  1968, p. 329.  1919",  Spectra April,  

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