UBC Theses and Dissertations

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UBC Theses and Dissertations

Search for galactic H2+ Sloan, David Scott 1969

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A SEARCH FOR GALACTIC H 2 + by DAVID S. SLOAN B.Sc., The U n i v e r s i t y of B r i t i s h Columbia, 1967 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n the Department of Phys i c s We a c c e p t t h i s t h e s i s as c o n f o r m i n g to the r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1969 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r an a d v a n c e d d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e a n d S t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d b y t h e Head o f my D e p a r t m e n t o r b y h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . D e p a r t m e n t o f Physics  The U n i v e r s i t y o f B r i t i s h C o l u m b i a V a n c o u v e r 8, C a n a d a Date A p r i l 1969 i i ABSTRACT The des ign and c o n s t r u c t i o n of a d i g i t a l a u t o -c o r r e l a t i o n spectometer for r a d i o astronomy is d e s c r i b e d . It is a 16 channel dev i ce with an o v e r a l l bandwidth of 2 IMiHz, Ex tens i ve use was made of i n t e g r a t e d c i r c u i t r y . The use of the spect rometer in a search for s i n g l y i o n i z e d molecu la r hydrogen (Hg*) i s d e s c r i b e d . The search covered a f requency range 1404 to 1409 MH:z for the r a d i o sources NML Cygnus and the Omega Nebula down to a l e v e l of T f e 0.25 K. i i i TABLE OF CONTENTS Chapter Page I I n t r o d u c t i o n ( i ) Hydrogen Ions in Space 1 ( i i ) Spectrometer and Rece i v ing System 2 II Spect rometer Development ( i ) Rece i v i ng System Block Diagram 5 ( i i ) Spectrometer B lock Diagram 6 ( i i i ) S i m p l i f i e d Analog to D i g i t a l Conver te r 7 ( i v ) A c t u a l Analog to D i g i t a l Conver te r 8 (v) M u l t i p l i e r Accumulator 10 ( v i ) Readout Gates 11 ( y i i ) Programmer and Te l e t ype Code Conver te r 12 ( v i i i ) Te l e t ype D r i v e r 15 III Phys i cs and Astronomy of H o + T r a n s i t i o n s ( i ) R ad i a t i on From H 2 * 16 ( i i ) L ine S t rengths and Number of H 2 + Ions 17 IV L ine Search Program and Resu l ts ( i ) Equipment T e s t i n g 21 ( i i ) Observ ing Program 22 ( i i i ) Data P rocess ing 23 ( i v ) C o r r e c t i o n fo r F a l s e D.C. Component 24 (v) van V leck and Hamming C o r r e c t i o n s 26 V Conc lus ions and Recomendations 28 B i b l i o g r a p h y 30 i v LIST OF ILLUSTRATI0NS F i g u r e Pa ge 1 B lock Diagram of Rece i v ing System 31 2 Spectrometer Block Diagram 32 3 S i m p l i f i e d Analog to D i g i t a l Conver te r 33 4 A c t u a l Ana log to D i g i t a l Conver te r 34 5 M u l t i p l i e r Accumulator 35 6 Readout Gates 36 7 Programmer and Te l e t ype Code Conver te r 37 8 T e l e t y p e D r i v e r 38 9 Rece i ve r I.F. Response 39 10 R e s u l t i n g Spec t ra 40 V ACKNOWLEDGEMENTS I would l i k e to express my s i n c e r e g r a t i t u d e to Dr , W. L. H. Shuter fo r h is he lp and guidance throughout t h i s work. I wish to thank the s t a f f of the Dominion Radio A s t r o p h y s i c a1 Observa tory for generous l y p r o v i d i n g t h e i r f a c i l i t i e s . I wish to thank P ro f . F. K. Bowers fo r h e l p f u l d i s c u s s i o n s on the spect rometer d e s i g n . 1 CHAPTER I INTRODUCTION ( i ) Hydrogen Ions in Space The hydrogen molecu la r ion H g + is of i n t e r e s t to r a d i o astronomy because of i t s p o t e n t i a l use in de te rmin ing the amount of molecu la r hydrogen in space . I t is b e l i e v e d that a l a rge p r o p o r t i o n (as much as 40% by some accounts ) of the hydrogen in the ga laxy might e x i s t as molecu la r hydro -gen. S ince the 21 cm atomic hydrogen obse rva t i ons have been so s u c c e s s f u l , a knowledge of the amount of mo lecu la r hydro -gen i s , important so that the t o t a l amount of hydrogen can be f i x e d . Unfortunate ly molecu la r hydrogen does not r a d i a t e at wavelengths i n s i d e any of the a tmospher ic windows through which we may make a s t ronomica l o b s e r v a t i o n s . H2 + on the other hand has many s p e c t r a l l i n e s in the r a d i o f requency band and i t is hoped tha t molecu la r hydrogen su r round ing s u i t a b l e sources might be e x c i t e d , perhaps in a manner anagous to OH. Two reg ions were s t u d i e d , one of these the Omega Nebula is a s t r ong HII r e g i o n which is thought to have no OH e m i s s i o n , the o t h e r , NML Cygnus is an i n f r a - r e d s t a r known to be a s t rong OH s o u r c e . The two s e l e c t e d reg ions were observed from 1404 to 1409 Mhz in f i v e o v e r l a p p i n g 2 MHz bands. The obse rv ing program was preceded by t e s t 2 obse r va t i ons of the hydrogen recombina t ion l i n e s 166 ©t^  and 167 i n the Omega s o u r c e . These have been observed by Palmer and Zuckerman ( r e f . 7) and served as a c a l i b r a t i o n of the i n s t rument . ( i i ) Spectrometer and Rece i v ing System 1) Rece i v i ng System The obse r va t i ons were made with the 25.6 meter p a r a b o l o i d a l t e l e s cope of the Dominion Radio A s t r o p h y s i c a l Observa tory near P e n t i c t o n . The r e c e i v i n g system was a v a r a c t o r d iode paramet r i c a m p l i f i e r rad iometer system deve loped by U. B. C. fo r use on t h i s t e l e s c o p e . Minor m o d i f i c a t i o n s of the r e c e i v e r were made to permit connec t ing the s p e c t r o -meter to the sys tem. 2) Spectrometer A very complete survey of the techniques of r a d i o a s t r o n o m i c a l spec t roscopy up to 1964 is g iven by A r g y l e (Re, 2) with s p e c i a l emphasis on a u t o c o r r e l a t i o n ( f o u r i e r t r ans fo rm) s p e c t r o s c o p y . S ince t h i s r ev i ew , analog techn iques have l a r g l y g iven way to d i g i t a l t e chn iques . The advantages of d i g i t a l methods in a u t o c o r r e l a t o r s are freedom from d r i f t s and e l i m i n a t i o n o f de l ay l i n e anomal ies (Ref . 2) and the easy achievement of v a r i a b l e bandwidths . Near ly a l l d i g i t a l spec t rometers have been of the so c a l l e d "1 b i t " type where input no ise is c l i p p e d u n t i l on ly the a l g e b r a i c s i g n of the input is p r e s e r v e d . Bowers (Ref. 6) has shown tha t s i g n i f i c a n t improvement in s i g n a l to no ise r a t i o can 3 be obta ined by p r e s e r v i n g more that one b i t in the q u a n t i z i n g of the input s i g n a l as shown in t ab l e one: Number of b i t s ' R e l a t i v e S i g n a l to Noise Ra t io R e l a t i v e Observ ing Time 1 2 3 O o 1.57 a. 1 3 1.04 1 . 0 0 Tab le 1 2.56 1.28 1.08 1.00 The p r i c e to be pa id for t h i s improvement is i nc reased comp lex i t y e s p e c i a l l y in the " m u l t i p l i e r s " (see be low) . The Dominion Radio As t rophys i c a1 Observatory were i n t e r e s t e d in a " low n o i s e " spect rometer fo r use in a Super Syn thes i s exper iment which they were p l a n n i n g . The des ign fo r the spect rometer d e s c r i b e d he re in grew out of d i s c u s s i o n s of a spect rometer for t h i s exper iment . Th i s spect rometer was b u i l t so that "2 b i t " as we l l as one b i t q u a n t i z a t i o n could be used to t e s t the f e a s i b i l i t y of t h i s approach . I t was hoped that " 2 b i t " q u a n t i z a t i o n which p rov ides a X X improvement in observ ing t ime , would be a s u i t a b l e t rade o f f . The dev i ce d e s c r i b e d below computes 16 po in t s of the ( co s i ne ) a u t o c o r r e l a t i o n f u n c t i o n . The un i t was used in an obse rv ing program with an o v e r a l l bandwidth of 2 Mhz. 4 Bandwidths from 6 Mhz to any sma l l e r bandwidth should be p o s s i b l e s imply by changing the " c l o c k " r a te and the band-pass f i l t e r ahead of the spec t romete r . The output of the spect rometer i s typed on a t e l e t y p e w r i t e r and punched on paper tape for input to a gene ra l purpose d i g i t a l computer. Th is computer computed the f o u r i e r t r ans fo rm to produce the power spect rum. 5 CHAPTER II SPECTROMETER DEVELOPMENT ( i ) Rece i v ing System Block Diagram As o u t l i n e d in f i g u r e 1, the s i g n a l i s c o l l e c t e d by the antenna and focused in to the " f e ed h o r n " . The e l e c t r i c a l s i g n a l from the feed horn is fed through the d i r e c t i o n a l coup le r to the v a r a c to r d iode paramet r i c a m p l i f i e r . Th i s a m p l i f i e r e s t a b l i s h e s the system noise temperature ( £ ^ 1 7 0 K) and p rov ides about 14 db g a i n . The next a m p l i f i e r i s an octave bandwidth t r a n s i s t o r a m p l i f i e r with enough ga in to overcome the l o s ses in the f i r s t m ixer . 4 A plasma d i s cha rge tube generates a 10 K no ise s i g n a l which is a t tenuated and added to the input s i g n a l by the d i r e c t i o n a l c o u p l e r . Th i s tube can be operated to p rov ide a c a l i b r a t i o n s i g n a l of 25K e f f e c t i v e antenna temp-e r a tu r e when d e s i r e d . The f i r s t l o c a l o s c i l l a t o r ( L .O . ) s i g n a l is generated in the c o n t r o l room by a phase- locked backward wave o s c i l l a t o r . Th is can be se t to any f requency in the 9 range 1 to 4 GHz with about 1 par t in 10 r e s o l u t i o n and a c c u r a c y . The f i r s t L .O. s i g n a l beats wi th the s i g n a l from the t r a n s i s t o r a m p l i f i e r to generate a 35 MHz (nominal ) i n t e rmed i a t e f requency ( I . F . ) s i g n a l . Th i s is a m p l i f i e d by a p r e a m p l i f i e r at the focus and a main a m p l i f i e r in the c o n t r o l room. The 35 MHz I.F. i s f u r t h e r mixed wi th a 45 .7 MHz 6 L.O. to generate an 11,0 MHz (nominally 10.7 MHz) I.F. Several 10,7 MHz bandpass f i l t e r s are provided and can be selected by a front panel switch. These f i l t e r s determine the radiometer bandwidth and have passbands ranging from 5 KHz to 6 MHz. For operation with the spectrometer, a special 2 MHz wide f i l t e r with sharp band edge's was used. This f i l t e r has been described elsewhere (Ref. 2), The bandshaped 11,0 MHz signal was mixed with an 8 MHz L.O. and passed through a 6 MHz low pass f i l t e r to provide a 2 to 4 MHz signal for the spectrometer. ( ( i i ) Spectrometer Block Diagram The input signal from the receiver enters the analog to digital converter where i t is sampled at the clock rate. The samples are quantized and changed to binary numbers. The digital signal is s p l i t into two paths. The f i r s t , the "prompt" line, goes to the f i r s t multiplier and the second, the "delayed" line, goes to the f i r s t multiplier and the f i r s t shift register stage. The shift register stores the binary number present at its input during one shift pulse until the next shift pulse. The sampling pulses and the shift pulses are synchronized and therefore the shift reg-ister functions as a digital equivalent of an analog delay line. The inputs to the N*th shift register are binary numbers corresponding to the present value of the input signal and the signal (N-l) shift periods earlier, Unlike an analog delay,line, the delay time of the shift registers 7 can be v a r i e d by changing the c l o c k f r equency . The m u l t i p l i e r produces the b ina ry product of the numbers p resent at i t s i n p u t s , and feeds t h i s number to the accumula to r . The accumulators sum these numbers for one i n t e g r a t i o n pe r i od of 5£, 1, 2, or 4 minutes . At the end of an i n t e g r a t i o n pe r iod the s to red sum is conver ted to 3 d i g i t o c t a l numbers and gated out channel by channel to the t e l e t y p e code c o n v e r t e r . Th is conver t s the o c t a l cha rac t e r to a 8 l e v e l code used by the t e l e t y p e w r i t e r , A page f o rma t t i ng c i r c u i t spaces the groups of 3 o c t a l c h a r a c t e r s and generates the l i n e feed and c a r r i a g e r e t u r n codes r e q u i r e d at the end of each l i n e . Between o u t p u t s , the t e l e t y p e w r i t e r i s f r ee for t yp ing a d d i t i o n a l data and remarks . ( i i i ) S i m p l i f i e d Analog to D i g i t a l Conver ter A s i m p l i f i e d A to D ( f u n c t i o n a l l y s i m i l a r to the "1 b i t " o p e r a t i o n of the a c t u a l A to D) i s shown in F i g , 3, The input s i g n a l i s fed to an i n t e g r a t e d comparator c i r c u i t . Th is c i r c u i t has the p roper t y that i t w i l l p rov ide a l o g i c a l 1 s t a t e at i t s output i f the input i s ^ 0 and l o g i c a l 0 s t a t e i f the input is •< 0, Th is "1 b i t " r e p r e s e n t a t i o n of the i n -put s i g n a l is sampled by ga t ing the input to the f l i p f l o p fo r 10 nsec . Th is f l i p f l o p holds the sampled va lue for the time between samples . The output of the f l i p f l o p is the input to the s h i f t r e g i s t e r d i g i t a l de lay l i n e . A f t e r the sample has been taken and the f l i p f l o p ' s output has s t a b i l i z e d , 8 the pu lse is a p p l i e d to the s h i f t r e g i s t e r s to s h i f t the new sample i n to the " d e l a y l i n e " . A f t e r a f u r t he r de lay to l e t the s h i f t r e g i s t e r s s t a b i l i z e , a pu lse samples the f l i p f l o p ou tpu t . Th i s pu lse is the "prompt " pu lse and is fed through va r ious a m p l i f i e r s to the 16 m u l t i p l i e r s . ( i v ) A c t u a l Analog to D i g i t a l Conver ter The a c t u a l A to D is shown in f i g . 4, i t i s s i m i l a r to the c i r c u i t d i s c r i b e d above but with the ex t ra c i r c u i t r y to permit " 2 b i t " o p e r a t i o n . Three comparators dec ide i f the input v o l t a g e , y, is g rea te r than -x , 0 and +x r e s p e c t i v e l y . Bowers has shown (Ref . 6) that the r e f e r e n c e v o l t a g e , x , shou ld be approx imat l y the rms va lue of the input s i g n a l but that the a c t u a l va lue of the vo l t age is not c r i t i c a l . The comparator outputs are sampled and held in f l i p f l o p s as above. The second compara to r ' s output becomes the second de l ay b i t and l o g i c gates determine i f the f i r s t b i t should be a 1 or a 0 a c c o r d i n g to t ab l e 2: Tab le 2 Input Comparator Output Delay B i t A B C 1 2 x<y 0 0 0 0 0 0<y<x 1 0 0 1 0 •x <y<0 1 1 0 0 1 y < - x 1 1 1 1 1 9 As d e s c r i b e d below, pu lses A, B, and C occur s e q u e n t i a l l y in time du r i ng each c l o ck p e r i o d ; These pu lses are c o n t r o l l e d by three f l i p f l o p s j u s t as the s i n g l e prompt pu l se was in the above case . These three separa te pu lses are combined in a three input gate and fed to a second three input ga te . Th i s gate has an i n h i b i t input from the readout programmer and a s t robe pulse input from the c l o ck c i r c u i t to c o n t r o l the pu lse w id th . The output of t h i s gate is the prompt pu lse and i s fed to d i s -t r i b u t i o n a m p l i f i e r s . The a c t u a l c lock input is 3 times the sampl ing r a te ( l e . 12 MHz). Th is c l o ck is fed to a d i v i d e by three c i r c u i t f a sh ioned from TTL f l i p f l o p s . Th is c i r c u i t and the l o g i c gates generate three pu lses wi th the t ime r e l a t i o n shown in the t im ing diagram below. These pu lses are s t robed with the c l o ck pu lse to become the three time s taggered pu lses A, B, and C. The (4 MHz) output of the d i v i d e by three c i r c u i t is termed "one c l o ck c y c l e " . The output of the d i v i d e by three c i r c u i t is f u r t h e r processed to become the pu lses that s h i f t the RTL and TTL s h i f t r e g i s t e r s . Va r ious TTL i n v e r t e r s were used to p rov ide sma l l ( 5 nsec) de lays as were r e q u i r e d in va r ious par ts of the c i r c u i t to i nsu re pu lses had the proper time r e l a t i o n with other p u l s e s . A t e s t swi tch connects the comparator inputs to +3.8 v o l t s . Th i s f o r c e s a l l three comparators to be in the one s t a t e so that c i r c u i t o p e r a t i o n can be checked . 10 (v) M u l t i p l i e r Accumulator D e s c r i p t i o n The b ina r y numbers to be m u l t i p l i e d by the m u l t i -p l i e r are present at i t s input in two d i f f e r e n t fo rms. The de layed number is r ep resen ted by a p a r a l l e l b i na r y form and i s s t o r ed fo r one c lock c y c l e in s h i f t r e g i s t e r s 1 and 2. The other number i s r ep resen ted by s e r i a l pu lses on the prompt l i n e . 0, 1, 2 or 3 pu lses may occur dur ing one c l o ck c y c l e . S h i f t r e g i s t e r 1 c o n t r o l s whether the prompt pulses are a l lowed to togg le accumulator stage 1 f l i p f l o p . S i m i l a r l y s h i f t r e g i s t e r 2 c o n t r o l s a gate which a l lows the prompt p u l -ses to pass to accumulator stage 2. The t r a n s i t i o n of accumu-l a t o r stage 1 output are d i f f e r e n t i a t e d by C I , Rl and the p o s i t i v e t r a n s i t i o n s are ored w i th gated prompt pu lses and fed to the input of accumulator stage 2. The accumulator c o n s i s t e s of a number of s c a l e s of two i e , b ina r y f l i p f l o p s . The f i r s t three stages as we l l as the s h i f t r e g i s t e r stage 1 and the l o g i c gates are TTL l o g i c for high speed . The remain ing 39 f l i p f l ops and s h i f t r e g i s t e r 2 are RTL l o g i c fo r low c o s t . For "1 b i t " ope r a t i on s h i f t r e g i s t e r 2 is he ld in the 0 s t a t e and the prompt pu lses are e i t h e r 1 or 0 i e . e i t h e r 1 pu lse or none. S ince s h i f t r e g i s t e r 1 is a TTL c i r c u i t and there are on ly 1/3 as many pu lses on the prompt l i n e , c l o ck speeds as high as 12 Mhz should be p o s s i b l e and bandwidths of 6 Mhz obta ined a l though th i s has not been t e s t e d . The m u l t i p l i e r accumulators are assembled two per 11 b o a r d o n e i g h t e t c h e d c i r c u i t b o a r d s . T h e s e p l u g i n t o a m o u n t i n g f r a m e s o t h a t t h e c i r c u i t s may b e e a s i l y c h a n g e d f o r s e r v i c i n g . F o r t h e t e s t s w i t h 2 b i t o p e r a t i o n , t h e s i x t e e n t h a c c u m u l a t o r was m o d i f i e d t o s u m t h e n u m b e r o n t h e p r o m p t l i n e , t o a l l o w t h e c o r r e c t i o n t o b e m a d e f o r t h e f a l s e D. C. t e r m a s e x p l a i n e d b e l o w . T h e m o d i f i c a t i o n c o n s i s t e d o f r e m o v i n g t h e c o n n e c t i o n f r o m t h e f i r s t d e l a y f l i p f l o p t o t h e g a t e c o n t r o l l i n g t h e p r o m p t l i n e a n d h o l d i n g t h i s g a t e o p e n . T h i s a l l o w e d a l l t h e p r o m p t p u l s e s t o e n t e r t h e a c c u m u l a t o r . T h i s i n e f f e c t m a d e t h e s p e c t r o m e t e r a 15 c h a n n e l d e v i c e a l t h o u g h r e a d o u t e t c . r e m a i n e d 16 c h a n n e l s . ( v i ) R e a d o u t G a t e s ( r e f e r t o F i g . 6 ) T h e l a s t t e n s t a g e s o f t h e a c c u m u l a t o r s a r e m o u n t e d p h y s i c a l l y o n t h e r e a d o u t b o a r d s . T h e s e t w o b o a r d s a l s o c o n t a i n t h e g a t e s w h i c h p e r m i t t h e c o n t e n t s o f t h e m o s t s i g n i f i c a n t d i g i t s t o b e g a t e d o u t s e q u e n t i a l l y t o t h e t e l e -t y p e c o n v e r t e r . T h e r e a d o u t p r o g r a m m e r g e n e r a t e s a 16 u n i t b i n a r y s e q u e n c e o n f o u r l i n e s ( A , B, C, D ) a n d t h e i r c o m -p l e m e n t s (X,"TF, T7, T T ) . T h i s s e q u e n c e s e l e c t s w h i c h c h a n n e l i s t o b e r e a d o u t . A f o u r i n p u t n a n d g a t e i s w i r e d t o t h e a p p r o p r i a t e c o m b i n a t i o n o f f o u r l i n e s t o r e c o g n i z e t h e b i n a r y a d d r e s s f o r t h a t c h a n n e l . W h e n t h e a p p r o p r i a t e a d d r e s s f o r t h a t c h a n n e l o c c u r s , t h e n a n d g a t e g o e s h i g h a n d t h e t h r e e 2 i n p u t g a t e s a r e e n a b l e d . T h e s e g a t e s a l l o w t h e c h a r a c t e r s e l e c t i o n p u l s e s (x, y , z ) t o e n a b l e t h e r e a d o u t g a t e s . 12 These pu lses read out the lowest accumulator f l i p f l o p s , s t a r t i n g with the th ree most s i g n i f i c a n t (x) and ending wi th the three l e a s t s i g n i f i c a n t ( z ) . The outputs of these gates are ored onto the output busses (4, 2, 1 ) , which are common to a l l c h a n n e l s , by the three input expanders . Note tha t when a readout c y c l e is t ak ing p l a c e , the input to the accumulators is i n h i b i t e d as des c r i bed in the A to D d e s c r i p t i o n above. Th is is r e q u i r e d because the changing of a s i n g l e accumulator f l i p f l o p dur ing readout can r e s u l t in a comp le te l y e r ron ious number be ing read out . At the end of each readout c y c l e , the programmer generates a pu l se which r e se t s the l a s t nine accumulator f l i p f l o p s to z e r o . The readout c y c l e l a s t s about seven seconds as determined by the t e l e t y p e w r i t e r p r i n t i n g speed and du r i ng th i s time one l i n e of output is p r i n t e d , ( v i i ) Programmer and T e l e t y p e w r i t e r Code Conver ter  ( r e f e r to F i g . 7) The t im ing for the programmer is de r i v ed from the 60 Hz power l i n e . The 6.3 V.,, 60Hz s ine wave i s conver ted to a square wave at TTL l o g i c l e v e l s by a Schmidt t r i g g e r made from an RTL l o g i c ga te . The 60 Hz square wave is d i v i d e d by two in a b ina r y f l i p f l o p and f u r t h e r d i v i d e d by three in a two stage s h i f t coun te r . The r e s u l t i n g 10 Hz waveform is conver ted to a narrow pu lse by ga t i ng in the two input nand ga te . The r e s u l t i n g 10 Hz pu lse is the bas i c t iming pulse for the programmer. Note that the model ASR 33 t e l e t y p e w r i t e r 13 accepts c h a r a c t e r s fo r p r i n t i n g at a 10 Hz r a t e . The 10 Hz pu lses are d i v i d e d by 100 in two F a i r c h i l d C JJ L 9958 decade d i v i d e r s and by 3 in a s h i f t c oun t e r , to produce one pu lse per 30 seconds . This is f u r t h e r d i v i d e d to produce one pu lse per minute , one per 2 minutes , and one per 4 minutes by a d d i t i o n a l b ina r y d i v i d e r s . A sw i t ch s e l e c t s which r a te w i l l c o n t r o l the readout ra te and hence the i n t e-g r a t i o n t ime . Each time the readout t r i g g e r o c c u r s , a sequence of events begins which goes as f o l l o w s : 1) p r i n t a l i n e of 16 words, each word c o n s i s t i n g of three cha rac t e r s and a space . 2) at the end of each l i n e , p r i n t a " l i n e f e e d " and " c a r r i a g e r e t u r n " symbol and generate a r e s e t p u l s e . Th is i s done in the f o l l o w i n g manner: The readout t r i g g e r turns on f l i p f l o p 2 and f l i p f l o p 3. F l i p f l o p 3 c o n t r o l s the p r i n t i n g ope r a t i on of the t e l e t y p e w r i t e r (see t e l e t y p e d r i v e r d e s c r i p t i o n ) . F l i p f l o p 2 opens a gate to a l low 10 Hz pu lses to reach a s i x stage b ina r y coun te r . The f i r s t two stages ( d i v i d e by f o u r ) and the app rop r i a t e two input g a t e s , generate the x, y, z and space c o n t r o l s i g n a l s . The next four stages ( d i v i d e by 16) p rov ide the A , B, C, D and A, B, C, D s i g n a l s which ( i n the readout boards ) s e l e c t the channel to be read ou t . At the end of 64 , 10 Hz p u l s e s , the D waveform is d i f f e r e n t i a t e d and a pu lse produced which turns o f f f l i p f l o p 2 ( s topp ing the coun te r ) and turns on f l i p f l o p 1. F l i p f l o p 1 opens a gate to a two stage counter which with the app rop r i a t e gates 14 generate the l i n e f e e d , c a r r i a g e r e t u r n and r e s e t s i g n a l s . The r e s e t s i g n a l turns o f f f l i p f l o p 3 ( and the t e l e t y p e ) and r e se t s the accumula to r . The output waveform H is d i f f e r e n t i a t e d and turns o f f f l i p f l o p 1 and the c y c l e ends . The t e l e t y p e code conve r t e r generates the proper outputs on s i x l i n e s which become s i x b i t s of the e i g h t b i t ASCII code which the t e l e t y p e w r i t e r r e c o g n i z e s . The other two l e v e l s are always 1 and 0. The l o g i c gates at the r i g h t hand s i d e of f i g u r e 7 generate outputs on the s i x l i n e s a c c o r d i n g to t ab l e 3: Tab le 3 Charac te r Leve l 123456 G 000011 1 100011 * 8 000111 9 100111 L. F. 010100 C . R. 101100 Space 000001 The i n f o r m a t i o n on l i n e s 1, 2 and 4 from the readout gates go d i r e c t l y to l i n e s 1, 2, and 3 qs the ASCII r e p r e s e n t a t i o n of numbers is b ina r y we ighted . The programmer 15 is l o ca ted in a s h i e l d e d box to the r i g h t of the p lug in c a r d s . ( v i i i ) The Te l e t ype D r i v e r ( r e f e r to F i g . 8) The t e l e t y p e d r i v e r is l oca ted i n s i d e the model ASR33 t e l e t y p e w r i t e r and con ta ins a l l the high power s e m i -conductors r e q u i r e d to operate the t e l e t y p e . The t e l e t y p e is commanded to p r i n t by ope r a t i ng a 115 v o l t ( reader t r i p ) r e l a y . The c i r c u i t shown at the top of f i g u r e 8 accompl ishes the i s o l a t i o n of the d e l i c a t e i n t e g r a t e d c i r c u i t l o g i c l e v e l s from the 115 v o l t power l i n e . The p r i n t command (from f l i p f l o p 3 in the programmer) l i gh ts a m in i a tu re long l i f e lamp. Th i s lamp causes the pho to- t r ans i s tor to conduct which turns on the b i - d i r e c t i o n a l t h y r i s t o r and operates the r e l a y . There i s no e l e c t r i c a l connec t i on between the l o g i c c i r -c u i t s and the r e l a y c i r c u i t and problems of t r a n s i e n t s from the power l i n e g e t t i n g in to the i n t eg r a t ed c i r c u i t s are avo i d e d . The model ASR33 t e l e t y p e has p r o v i s i o n fo r e n t e r i n g data by grounding one or more of the e i g h t input l i n e s a c c o r d -ing to the ASCII code (tape reader i n p u t ) . E i g h t PNP power t r a n s i s t o r s are used to i n t e r f a c e between the l o g i c l e v e l s and the t e l e t y p e v o l t a g e s . Note tha t the normal ly f l o a t i n g t e l e t y p e s i g n a l power supply is grounded at th i s po in t but t h i s i s of no concern as long as the t e l e t y p e is not used fo r any other purpose . 16 CHAPTER I I I PHYSICS AND ASTRONOMY OF Hn TRANSITIONS ( i ) R a d i a t i o n from H 2— S o m e r v i l l e (Ref . 3) has g iven the c o u p l i n g scheme fo r H g + as the so c a l l e d b^j scheme, where J_ and S_ coup le to form F_2 and £2 and N_ couple to form F» The s i m p l i f i e d l e v e l diagram fo r Hg+ in the N=l r o t a t i o n a l s t a t e ( the lowest s t a t e g i v i n g r a d i o f requency t r a n s i t i o n s ) and the V=0 s t a t e , is sketched below £2 •4 Va. S o m e r v i l l e has c a l c u l a t e d the t r a n s i t i o n probab-i l i t i e s for the p o s s i b l e t r a n s i t i o n s and shown that the most i n t ense w i l l be 17 and t h a t t h e E i n s t e i n A c o e f f i c i e n t f o r t h i s t r a n s i t i o n i s -IS -I The s p i n H a m i l t o n i a n f o r t he s y s t e m can be e x p r e s s e d as j -i> ~* U s i n g S o m e r v i l l e ' s v a l u e s f o r b & c and t h e e x p e r i m e n t a l v a l u e f o r d o b t a i n e d by J e f f e r t s ( r e f . 1 2 ) y r 000. 7 C z ( Z ? . 0 IMHJ, t h e p r e d i c t e d f r e q u e n c y i s t h e n Vo * 76 l * '*40 C 1 Yy '<L SIHj, u s i n g the b e s t v a l u e f o r d g i v e s The r a n g e s e a r c h e d i n c l u d e s t h i s v a l u e and t h e v a l u e Vp z 1405 MHz upon w h i c h P e n z i a s e t a l . ( r e f . 8 ) b a s e d t h e i r s e a r c h . ( i i ) L i n e S t r e n g t h s and Number o f H2+ i o n s . F o r a c l o u d o f t e m p t e r a t u r e 7"^  t a n ( j o p t i c a l d e p t h f 18 t h e e x p e c t e d a n t e n n a t e m p e r a t u r e i s I f t h e c l o u d i s o p t i c a l l y t h i n ( 7"V< I ) T o f i n d a n e x p r e s s i o n f o r "7" we u s e B a r r e t ' s ( R e f . 5) e q u a t i o n f o r t h e a b s o r p t i o n c o e f f i c i e n t : c k r w h e r e Y*0??- i s t h e a b s o r p t i o n c o e f f i c i e n t p e r i o n 7 x 0 i s t h e n u m b e r p e r c c . o f i o n s i n t h e s t a t e oi i s t h e E i n s t e i n B c o e f f i c i e n t f{y) i s t h e 1 i n e s h a p e f u n c t i o n i s t h e o b s e r v i n g f r e q u e n c y T " i s t h e c l o u d t e m p e r a t u r e . s i n c e ' -fvc*)jut. we h a v e c k r w h e r e N i s t h e t o t a l n u m b e r i o n s i n t h e u p p e r s t a t e i n a * c o l u m n . 19 From Condon and S h o r t l e y (Ref. 4) we have : P°' ~ <r - , Rio where f_!L i s the r a t i o of the s t a t i s t i c a l weights fo r the two h y p e r f i n e l e v e l s = 3 . A J O i s the E i n s t e i n A c o e f f i c i e n t . S u b s t i t u t i n g we have p u t t i n g t h i s i n equa t ion ( 1 ) , f TT V c A T S -no- ' « T — : >0 i f we assume the l i n e to be a g a u s s i a n , I w h e r e / i V is the gauss i an f u l l width at h a l f maximum. We get a va lue of A J Q from Sornmervi l le ( r e f . 3) of Pi to ~ 3 i 63 X lO*1* 20 I f i s the number i n the s t a t e ( F 2 , F) (3/2, 5/2) t h e i the number i n the ground s t a t e i s g i v e n by: Hi. 6 -where V'-i? i s the energy gap between the N = 0 and N - 1 l e v e l s . s u b s t i t u t i n g f o r and t h e r e f o r e we get f o r r 21 CHAPTER FOUR LINE SEARCH PROGRAM AND RESULTS ( i ) Equipment T e s t i n g In order to r e s o l v e low i n t e n s i t y s p e c t r a l f e a t u r e s , i t i s necessary to have a system whose ampl i tude response as a f u n c t i o n of f requency is very f l a t . In order that a v a r i a t i o n of 0.2 K be l a rge (say 10 t imes ) compared with the system no ise background ( £ ^ 2 0 0 K) the f requency r e s -ponse must be f l a t to 0 .1% . The obse rv ing techn ique used ( t ak ing a d i f f e r e n c e spectrum) helps but because of e q u i p -ment d r i f t s e t c . , a good f requency response is s t i l l a major conce rn . S ince i t would r e q u i r e unreasonably high c i r c u i t Q*s fo r the 1400 Mhz R.F. s tages to a f f e c t the gassband wi th e f f e c t s important over a two Mhz range , the f requency r e s -ponse of the R.F. stages was not measured in d e t a i l at t h i s t ime . The ampl i tude response of the r e c e i v e r I.F. a m p l i f i e r s i n c l u d i n g the added I.F. system for the spect rometer was measured. F i g u r e 9 shows the response from 35 Mhz input to output to the spec t rome te r . From th i s i n f o rma t i on the sampl ing f requency was ad jus ted to be 12 Mhz so that a l i a s i n g (Ref. 1) occured at the 20 db. po in t and a l l f o lded s p e c t r a l components were a t tenua ted by at l e a s t that amount. B) Other t e s t s 22 The spec t rometer was f u r t h e r t e s t ed by f eed ing cons tan t ampl i tude s i n e waves i n t o the 35 Mhz I.F. system with the spec t rometer a t t a c h e d . F requenc ies from 33 to 36 Mhz, in 10 Khz steps were used . The spect rometer output in each case was processed to produce a spectrum as d e s c r i b e d below. These s p e c t r a were i n spec ted to insure that the peak ampl i tudes c o r r e c t l y d e p i c t e d the I.F. ampl i tude r e s -ponse ( f i g , 9) and were f ree from any anoma l i e s . Fu r the r t e s t i n g used the whole r e c e i v e r system and is d e s c r i b e d below. ( i i ) Observ ing Program As a p r e l i m i n a r y s tage of t e s t i n g the spec t rome te r , p r o f i l e s jo'f the 21 cm atomic hydrogen l i n e were taken . S ince th i s l i n e is t y p i c a l l y 100 K, t h i s p rov ided a measure of the o v e r a l l performance of the system but no i n d i c a t i o n of i t s u se fu lness for obse rv ing very low i n t e n s i t y l i n e s . The r e fo r e a t e s t was made by l o o k i n g fo r recom-b i n a t i o n l i n e s ( n y n - 1 ) of hydrogen in the Omega Nebu la . Palmer and Zucherman (Ref, 7) have observed these l i n e s at Ha r va rd , We observed H16<7< at 1399.4 Mhz and H166 at 1424.7 Mhz in the Omega Nebula s o u r c e . These two l i n e s b racke td our planned search f requency range , and s i n c e they had antenna temperatures of 0.4 K and were c l e a r l y r e s o l v e d , we began our search f o r Hg* . The sea rch c o n s i s t e d of 20 minutes on the source and 20 minutes with the antenna moved one degree north in 23 d e c l i n a t i o n . The spectrum taken o f f the source was then s u b t r a c t e d from that taken on the source to e l i m i n a t e spur ious responses from the equipment. A f t e r each 40 minutes of o b s e r v i n g , the r e c e i v e r was tuned 1 Mhz h igher in f requency and the pa t t e rn r epea t ed . S ince the s p e c t r o -mete r ' s bandwidth is very nea r l y 2 Mhz, a 50% ove r l app ing of each spectrum was ob t a i ned . The Omega Nebula was o b s e r -ved from 1404 to 1409 Mhz in th i s manner on two separa te o c c a s i o n s . The i n f r a r e d s t a r NML Cygnus was a l so observed in th i s manner but on ly one complete spectrum was taken . To f u r t h e r e l i m i n a t e spur ious r e sponses , the two o b s e r v a -t i ons of Omega were s h i f t e d in f requency by 300 Khz. ( i i i ) Data P rocess i ng The spec t rometer p rov ides a l i n e of output p r i n t e d on the t e l e t y p e w r i t e r every 30 seconds to 4 minutes as d e s i r e d . The output ( a u t o c o r r e l a t i o n c o e f f i c i e n t s ) are a l s o punched on paper tape by the t e l e t y p e and th i s tape was fed i n to the computer wi thout any p r o c e s s i n g . In the computer the l i n e s of data on the source were averaged and the f a l s e D. C. component was computed and sub t r a c t ed from each c o -e f f i c i e n t . A s i m i l a r c o r r e c t i o n was made fo r the o f f source d a t a . The data taken o f f the source was sub t r a c t ed from the on source data and the van V leck and the Hamming c o r r e c t i o n s (see above) were per formed. The cos ine f o u r i e r t r ans fo rm of the data was computed us ing a program w r i t t e n by A. C. Gower. Th is program took the 16 a u t o c o r r e l a t i o n c o e f f i c i e n t s and 24 computed a 31 p o i n t power spectrum. The on and o f f s o u r c e s p e c t r a and the d i f f e r e n c e spectrum were punched on paper tape and p r i n t e d by the computer. The above p r o c e s s i n g was done on s i t e a t D. R. A. 0. u s i n g t h e i r P. D. P. 9 computer, f u r t h e r p r o c e s s i n g was done at the U, B. C. computing c e n t e r . The computer programs were not unique and are not i n c l u d e d here. T y p i c a l l y the d i f f e r e n c e s p e c t r a had a s l o p i n g b a s e l i n e w i t h an a p p r o x i m a t l y one degree K/ Mhz s l o p e . The i n d i v i d u a l s p e c t r a were examined by eye and the end p o i n t s of the f l a t p a r t were p i c k e d . A computer r o u t i n e s u b t a c t e d a s t r a i g h t l i n e through the e n d p o i n t s and " r e j e c t e d " the end d a t a . S i n c e i n d i v i d u a l s p e c t r a o v e r l a p p e d by 50% no p a r t of the t o t a l spectrum was l o s t . The computer p r o -gram then j o i n e d up a d j a c e n t s p e c t r a and s u b t r a c t e d a b e s t f i t s t r a i g h t l i n e from the t o t a l spectrum. The r e s u l t i n g s p e c t r a a l o n g w i t h the 166 and 167 •< r e c o m b i n a t i o n l i n e s are shown i n f i g u r e 10. ( i v ) C o r r e c t i o n For F a l s e D. C. Component Of c o n s i d e r a b l e concern i n t h i s type of s p e c t r o -meter i s the f a c t t h a t p o s i t i v e a r i t h m e t i c i s used to r e p -r e s e n t the i n p u t v o l t a g e samples. The samples are g i v e n the v a l u e s 0 or 1 a c c o r d i n g to whether the sample i s g r e a t e r to or l e s s than z e r o . ( T h i s i s f o r the "1 b i t " case but the same argument holds f o r the "2 b i t " c a s e ) . T h i s i s done to reduce the hardware r e q u i r e m e n t s . Simple ac c u m u l a t o r s are of the "up c o u n t e r " t y p e . "Up-down" c o u n t e r s which can 25 s u b t r a c t counts fo r negat i ve inputs are much more expens i ve . I f no i se with a f l a t spectrum (over the 2Mhz band -width ) i s fed in to the a u t o c o r r e l a t o r i n p u t , the product formed in the f i r s t channel m u l t i p l i e r w i l l be the square of the input to the de lay and prompt l i n e s and t he r e fo r e the 2 2 products G and 1 are e q u a l l y l i k e l y (0 and 1 ) i e , the chance of a 1 is 0 , 5 . I f t rue a r i t h m e t i c had been used , 0 and 1 would each occur with equa l l i k e l i h o o d and the products 0, 0, 0, 1 would have equa l chance , i e „ the p r o b a b i l i t y of a 1 would be 0 .25 . Th is ext ra number grows in each channel even when there is no s p e c t r a l i n f o rma t i on p r e s e n t , and i t has been termed the " f a l s e D.C. component" . I t i s the nature of the f o u r i e r t r ans fo rm that t h i s term w i l l t r ans fo rm to a l a rge s i g n a l at zero f requency ( D . C . ) . Th is term has a s i n x / x form and is u n d e s i r a b l e for two r e a s o n s : F i r s t , the width of t h i s term masks s p e c t r a l i n fo rma t i on of a low f r e -quency. More important for the a p p l i c a t i o n s tha t were planned fo r t h i s spec t rome te r , the s i d e l o b e s of t h i s term r i n g at a low l e v e l throughout the whole f requency band and s i n ce these s i d e l o b e s would be many times the ampl i tude of the expected s p e c t r a l f ea tu res they cou ld not be t o l e r a t e d . I t is necessary that t h i s term be sub t r a c t ed from the data ( c o r r e l a t i o n c o e f f i c i e n t s ) be fo re the f o u r i e r t r ans fo rm is per fo rmed. The f o u r i e r t rans fo rm is very s e n s i t i v e to th i s term and i t was dec ided tha t some method of r e c o r d i n g the f a l s e D. C. was r e q u i r e d . For the t e s t s made with "2 b i t " o p e r a t i o n , the 26 l a s t (16th) channel was mod i f i ed to count not the products of the de layed and undelayed numbers but the numbers on the prompt l i n e o n l y . Th is m o d i f i c a t i o n is d e s c r i b e d in the d e s c r i p t i o n above. When the c o r r e l a t o r was used as a "1 b i t " machine, (as i t was fo r the work r epor ted h e r e i n ) the above m o d i f i c a t i o n was not r e q u i r e d and the 16th channel was r e -turned to normal . S ince the f a l s e D.C. in t h i s case is one-h a l f the va lue of the f i r s t c h a n n e l , the only c o r r e c t i o n r e -qu i red was to s u b t r a c t one-ha l f the f i r s t c o e f f i c i e n t from a l l the c o e f f i c i e n t s . (v) van V leck and Hamming C o r r e c t i o n s The a u t o c o r r e l a t i o n c o e f f i c i e n t s are processed in two ways p r i o r to the f o u r i e r t r a n s f o r m . The need for the van V leck c o r r e c t i o n may be seen by c o n s i d e r i n g the e f f e c t of one b i t q u a n t i z i n g on a sinewave i n p u t . The i n -put s i g n a l is c l i p p e d to a square wave of cons tan t ampl i tude by the A to D c o n v e r t e r . The a u t o c o r r e l a t i o n f u n c t i o n of a square wave is a triangle wave. The van V leck f u n c t i o n c o n -ve r t s the t r i a n g l e wave to a s i n e ( a c t u a l l y a cos ine wave because the t r i a n g l e wave s t a r t s at a maximum) which the c o r r e l a t i o n f u n c t i o n would have been i f the d l i p p i n g had not o c c u r e d . The only deg rada t i on for a s t a t i o n a r y no ise s i g n a l is a r e d u c t i o n in the s i g n a l to no ise r a t i o ci. (Re. 6, 9 ) . The a u t o c o r r e l a t i o n f u n c t i o n has the p rope r t y that the c o e f f i c i e n t of the f i r s t channel is as l a rge or l a r g e r than any other channe l . The c o e f f i c i e n t s can be 27 normal ized t he r e fo r e by d i v i d i n g a l l channels by the magnitude of the f i r s t c h a n n e l . The so c a l l e d van V leck c o r r e c t i o n can then be per fo rmed. It c o n s i s t s (Ref . 9) of r e p l a c i n g the normal ized c o e f f i c i e n t C by the f u n c t i o n The co r r e spond ing c o r r e c t i o n for "2 b i t " ope r a t i on w i l l be comp l i ca ted i n v o l v i n g two t r i a n g l e waves and w i l l c r i t i c a l l y depend on the o p e r a t i n g po in t of the second d e c i s i o n l e v e l in the A to D c o n v e r t e r . The second c o r r e c t i o n performed is the g rad ing of the c o r r e l a t i o n c o e f f i c i e n t s which is r equ i r ed to reduce the s i d e l o b e s of the f o u r i e r t r ans fo rm . Th is po in t is d i s -cussed in d e t a i l in r e f . 1. The c a l l e d Hamming f u n c t i o n was chosen . Th i s is g iven by the ope ra t i on where the c o -e f f i c i e n t of the n ' th channel C„ is r ep l aced by C ^ * [ o . S ¥ + 0-i6 x c , s (C"~'1*lr ) J where n ranges from 1 to 16. 28 CHAPTER FIVE CONCLDSIONS AND RECOMMENDATIONS ( i ) H? + Search F i gu re 10 shows the f i n a l spec t r a obta ined for the Omega Negula and NML Cygnus. Theses suggest than an upper l i m i t of T^ = 0.25 K (^-5 s tandard d e v i a t i o n s ) can be ass igned to these r e g i o n s . Th is is e q u i v i l e n t to 3.3jt>e ions 2 + in a cm column. Al though no Hg was found in t h i s search nor in that of Penzias et a l (Ref . 8) i t i s f e l t that f u r t h e r e f f o r t s shou ld be made to de t e c t i t because of the importance i t s d e t e c t i o n might have in the unders tand ing of p h y s i c a l p rocesses in i n t e r s t e l l a r space . It i s noted that more theo -r e t i c a l work to r e f i n e the f requency p r e d i c t i o n is important as t h i s w i l l reduce the f requency range which must be searched and permi t more sources to be s t u d i e d . ( i i ) Spectrometer The spect rometer worked as expected a f t e r an i n i t i a l pe r i od of " debugg ing " was completed . Some component f a u l t s which at f i r s t were a t t r i b u t e d to component f a i l u r e s , were l a t e r shown to be a r e s u l t of a power supply go ing out of r e g u l a t i o n . The i n t e r f a c i n g of TTL to RTL l o g i c l e v e l s was found to be s e n s i t i v e to l o ad ing by the RTL f l i p f l o p s . Th is was cured by adding an RTL b u f f e r a m p l i f i e r between the two c i r c u i t s . The TTL c i r c u i t which ored the d i f f e r -2 9 e n t i a t e d pu lse and the prompt pu lse in the m u l t i p l i e r s was found to be s e n s i t i v e to pu lse amp l i t ude . Th i s was because t h i s gate was ope ra t i ng near the upper f requency l i m i t for TTL c i r c u i t s . The d i f f e r e n t i a t o r c i r c u i t had to have com-ponents i n d i v i d u a l l y s e l e c t e d and was very s e n s i t i v e to the prompt pu lse w id th . A TTL l o g i c gate c i r c u i t that might a l l e v i a t e the problem is shown below a l though i t has not been t e s t ed in the a c t u a l c i r c u i t . The readout g a t e s , programmer and t e l e t y p e d r i v e r worked very we l l except for some i n t e r f e r e n c e from no ise on the power l ine g e t t i n g in to the 60 Hz t r i g g e r gene r a to r . S imple R.C. low pass f i l t e r i n g removed the n o i s e . Recent t rends in i n t e g r a t e d c i r c u i t s have been towards lower p r i c e s fo r TTL c i r c u i t s so the cos t advantages fo r RTL is no longer so c l e a r . C o n s i d e r i n g the wide range of a v a i l a b l e TTL c i r c u i t s and t h e i r advantages of speed and no ise immunity, f u tu r e inst ruments of t h i s type would probab ly b e n e f i t from us ing TTL c i r c u i t s e x c l u s i v e l y . 30 BIBLIOGRAPHY 1) B lackman, R. B. and Tukey J . W , " T h e Measurement of Power S p e c t r a " N. Y. C. Dover (1958) . 2) A r g y l e , P. E. Ph.D. Thes i s 0. B. C. , (1964) . 3) S o m e r v i l l e , W. B. , Mon. Not . R. a s t r o . S o c , 139. 163 (1968) 4) Condon, E. D. and S h o r t l e y , G. H . , "The Theory of Atomic S p e c t r a " , Cambridge U n i v e r s i t y P r e s s , (1964) . 5) B a r r e t t , A. H . , P roc . IRE, 46 . 250. (1958) . 6 ) Bowers, F. K., P r i v a t e Communicat ion. 7) Pa lmer, P., Zuckerman, B. , Na ture , 209. 118, (1966) . 8) P e n z i a s , A. A . , J e f f e r t s , K. B., D i c k i n s o n , D. F . , L i l l e y , A. E . , and P e n f i e l d , H. Ap. J . , 154. 389, (1968) . 9) van V l e c k , Radio Res. L a b . , Harvard U n i v e r s i t y R e p t . , #51, (1943) . 10) Weinreb, S . , P roc . IRE, £ 9 , 1099, (1961) . 11) Shu te r , W. L. H . , S l o a n , D. S. Can. J . P h y s . , In the P r e s s . 12) J e f f e r t s , K. B. , Phys. Rev. L e t t e r s , 2_0, 39 , (1968) . 25. G M PARAB. > 1 \ S T L . O . 1ST U . O . i DIODE O C T A V E 1 P R E | PAR-AMP T R W S . A M P AMP . S 5 MHfl F T ATT EN. V A MIXER P L A S M A N O V S E T U B E o I.F. AMP 10.7 B P F 7.7 M H ^ o s c . 6WlH-j. L P r 2 \-.o. N O M I N A L \0.7.MH^ I.F. T O SPECTROMIET^ T O E * \ S T . R E C E I V E R _ . . I PULSE <3cN S P E C T R O M T R T T Y S H I F T R E G I S T E R S M U L T I P L I E R S A C C U M U L A T O R S R E A D O U T £>ATES < j 0 SELECTOR C O D E CONVERTOR T T Y T T Y D R I V E R R F . I N P U T 4 MHi P U L S E -0 -R E A D O U T . \HH\B\T DELAY - O -o -o--o-P R O M P T LINE.S T O E A C H O R C U I T C A R D E> S . f ? . S H I F T P U L S E Ik w ^ — :+ Q U-0 o 0 o h D 0-z A c t u a l A t o D C o n v e r t e r F i g u r e h 35 > > SHIFT REGISTERS >—1 -> > r M P S SS2. L-{>-V c "PROMPT L\HE cc V TO READOUT S A T E S F i g u r e 5 M u l t i p l i e r A c c u m u l a t o r 36 7ACCI \ N V 0-S u-I 0; J 0 D 0 0 A S E T On 1> 0 — M 0 — > 2 o— A A BB c c DD <KJ=—<Y R e a d o u t g a t e s . f i o u r e 6 i i , i I I t i > i i i • i 9 37 A . Z 0 i A A Q O O O A 1 ui V h h 3 0 0 < UJ —W— f t v<rx IUJIU-Q CD i _ j r V V -K -i>—1 IT* - V V H i ' L - L ~ LI) .|10 •cr 10-m "D—P—0- N U-UJ 0 o. 0 -» u 4 ) — p — p — CO c-jnurp 7 P r o g r a m m e r a n d T e l e t y p e f i g u r e / fcode C o n v e r t e r ' 38 F P T - IOO MAC-5 - W A r rW W R E A D E R T R I P JLSJb 1 US V A - . C . 4 T E L E T Y P E D R W E R r r 8 T . E L E T Y P _ E Figure 8 Teletype Driver 39 R e s u l t i n g I.F. R e s p o n s e F i g u r e 9 

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