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Memorandum M- 1 5 1 1 ~ l l k l XO Page 1 of 4

D i g i t a l Computer Laboratory \ ClASSlFVCATlW* &**} Massachusetts I n s t i t u t e of Technology

Cambridge, Massachusetts

TO:

By. Date: Jl -lz£t-£-

SUBJECT: WWII B10CK DIAGRAMS GROUP MEETINGS OF MAY 27 & 29 AND JUNE 3 . 1952

T o : WWII Planning Group

From: W. A . Hosier

Da te : June A, 1952

Abs t rac t : Th i s note summarizes the d i scuss ion a t the above meetings f o r the benef i t of t h o s e whc^aajLjdEsh^ t o t race t h e course of thought on t h e subject.

P resen t : May 2 7 :

G. R. A. J . W. J . R. W. N.

R. Briggs C. Jeffrey K a t z V . Harrington A . Hosier J a c o b s P . Mayer N. Papian H. Taylor

W J R R W N

J . Harr ington, l e a d e r of Lincoln group 24, had been asked t o speak t o us on the gene ra l subjec t of radar da ta t r ansmiss ion . He began by point ing o u t how the method chosen t o transmit t h i s data depends both on the q u a l i t y and quantity o f the data. I f a typical r a d a r of the Cape Cod net saw nothing b u t nice, c l e a n t a rge t s , s ay 50 of them p e r 5-second s c a n , or an average of 1 0 per second, and the p o s i t i o n of each t a r g e t were represented by a 16 -d ig i t number, t h i s would require t ransmission of 160 d i g i t s p e r second, and could b e done on a te lephone l i n e of no more t h a n 200 cycles bandwidth.

I f , on the other hand, the area surveyed by t h e radar , which i s quantized i n t o some 16,000 elements , i s 10Jf f i l l e d by a i r c r a f t and ground c l u t t e r , t h i s g ives 1600 words to t ransmit ins tead of 50, and of course o n l y the 50, o r 3%, are u s e f u l . Unless something were done about i t , t h i s would require over 6000 c y c l e s bandwidth t o t ransmit every th ing .

There i s further t h e problem of r e c e i v r f V > i s e mixed in w i th s i g n a l s , b u t for tuna te ly t h i s has been v i r t u a l l y s o l v e d # w \ a i t a b l e i n t e g r a t i o n and c l ipp ing , so t h a t false t a r g e t s due to noiajaAye^ of n e g l i g i b l e number.

C I f iy$A T i A 8. SECURITY INFORMATION

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M T U l Memorandum M-1511 ^ ^ ^XT\ j P ^ lt= UVl U U inl IL Page 2

Ground c l u t t e r and ra ins torms , however, do present d i f f i c u l t y . In t rying t o choose between t r ansmi t t ing a binary number and slowed-down video (which requires one possible pulse per scan for every quantized area element), observe t h a t i f fn represen t s the bandwidth required t o pass b inary d i g i t s , and fv that r equ i r ed for slowed-down v ideo , N the number of quantized area e l e m e n t s , T the t ime in seconds per antenna scan , and ex the f r ac t ion of the a r e a "occupied" w i th s i gna l s , we may wri te

fD =<*N log2 N ; fv • J L % ft) =cxlog 2 N T T fv

with 256 x 64 = 2** elements of a r e a , log2 N = 14, so tha t fj) = fy implies <X= l / H • . 0 7 . Which i s to say, i f l e s s than 7% of the area i s to be t ransmit ted as t a rge t s and c l u t t e r , a binary coded s ignal i s bes t to send over the te lephone l i n e s ; but i f more than 7% of the area i s to be s e n t , then slowed-down video (SDV) i s p r e f e r a b l e . As i t happens, with present MTI and o t h e r c lu t t e r - e l imina t ion techniques , more than 7% ge t s through, and SDV i s current ly necessary . But i n 2 years or l e s s , i t seems reasonably certain t h a t MTI wi l l be improved t o the point where l e s s than 7% w i l l ge t through, and binary coded s ignals w i l l be preferab le in most cases . Harr ­ington suggested tha t we might with p r o f i t v i s i t t h e CAA's i n s t a l l a t i o n of an ASR-2 a t Logan a i r p o r t . This has an MTI which gives only 20 db s u b - c l u t t e r v i s i b i l i t y bu t wil l do t h i s r e l i a b l y ; usua l ly no more than 10 f a l s e s igna l s show on t h e PPI.

Even with such improvement, i t ip u n l i k e l y tha t coded binary t ransmission wi l l e n t i r e l y supersede SDV, for two reasons: f i r s t , SDV i s simpler, r e q u i r i n g perhaps 100 tubes per radar as aga ins t 600 for a coded binary sys tem. Second, the coded b inary system i s " sa tu rab l e " ; a sudden increase i n signals due t o a i r c r a f t or jamming might produce more data than could be t r a n s m i t t e d , w i th the r e s u l t t h a t some des i red s igna l s might never get through a t a l l . Therefore , Harrington th inks t h a t the f i n a l system w i l l probably have SDV a t smal l r ada r s , l eaving the more complicated binary i n s t a l l a t i o n s to la rge r a d a r s , whose l a rge coverage area makes i t uneconom­ica l to u s e SDV. I t seems l i ke ly t h a t as long as telephone l i n e s are used , data w i l l always be t r ansmi t t ed s e r i a l l y in pulses of about 500 ,us.

Experiments a r e going on, says Harr ington, to ob ta in b e t t e r angle readings from the radar— to the order of l / l 0 ° . This i s p a r t i c u l a r l y necessary f o r e levat ion read ings . I t i s s t i l l undecided whether "nodding beam" or "V-beam" he igh t f inders a re b e s t , and whether i t i s b e t t e r to have height d a t a come through automat ica l ly or only when requested by the computer. WWII, he b e l i e v e s , should have the f a c i l i t y for request ing height da ta , and th is a t a maximum r a t e of about four i n t e r roga t i ons per second. V-beam height d a t a probably cannot be expected to be more accurate than 1000 f t . ; in sp i te of t h i s , Harr ington fee l s t h a t V-beam w i l l probsbly be the f i n a l system because of i t s g r e a t e r s i m p l i c i t y .

P r o j e c t Lincoln has r ecen t l y receitwd a CPN-18 radar— one of a type which Harrington t h i n k s wi l l becorae^Mj£\pBckbone of the Cape Cod system". This set has MTI and a rapii^rSpfinVVate (23 rpm).

N T D A l

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•s> „-«-.«« O i l M W T D M P a g e3

I t i s doub t fu l , said Harrington, whether we can be very d e f i n i t e a b o u t terminal equipment u n t i l a t l eas t a year from now* Some aspec ts of i t s u c h as b e t t e r MTI may wel l take longer. In any event i t i s l i k e l y t o be complex and expens ive , and i f we have any choices to make between adding memory to WWII o r more terminal equipment, we w i l l probably do b e t t e r t o t a k e the f i r s t a l t e r n a t i v e .

In conc lus ion , Mr. Harrington reminded us tha t even i f i t seems p o s s i b l e , i t would be a mistake to t ry to make an a i r defense system e n t i r e l y a u t o m a t i c . Problems of c l u t t e r , t a rge t i n i t i a t i o n , or concent ra t ion on a r e a s of g rea tes t t a r g e t dens i t y are eas i ly handled by human ope ra to r s , and f o r t h i s reason i t i s highly des i r ab l e to keep a scope on the end of each r a d a r input. The objective should be, not an automatic system, but a balanced s y s t e m , in which rou t ine opera t ions are done automat ical ly and more complex d e c i s i o n s are made by the o p e r a t o r s .

At the May 29 meeting, which was b r i e f , several r a t h e r unre la ted q u e s t i o n s were b rough t up:

W. Pap i an emphasized again tha t the memory group would p r o f i t l i t t l e from the 256- reg i s t e r memory t e n t a t i v e l y planned for WWIA, and would have t o devote t i m e to bui lding i t that would be be t t e r devoted to the l a r g e WWII memory. He suggested t h a t for t h e purpose of t e s t i n g other components assembled into a WWIA, i t might su f f i ce to have a 3 2 - r e g i s t e r memory analogous t o t e s t s to rage in WWI. This could be b u i l t out of cores w i t h o u t great d i v e r s i o n of e f f o r t , and would fu r ther serve the twofold p u r p o s e of a f fo rd ing the shop p rac t i ce in working with cores and helping t o develop t rouble-shoot ing techniques .

Ex t rapo la t ion of WWI methods, i t was speculated, would y ie ld a WWII arithmetic element of some 2000 tubes . N. Taylor wns su r e , however, t h a t a third or s o of these could be pared off by omitting buffer ampl i f ie rs and some extra g a t e s , and s u b s t i t u t i n g c r y s t a l diodes wherever p o s s i b l e . T h i s -vould be f a c i l i t a t e d by u s i n g lower pu l se l e v e l s , of the order of one v o l t (instead of t h e 20 vol t s used in WWI), and perhaps by using d i f f e r e n t t u b e s such as t h e 6AK5 in some a p p l i c a t i o n s .

I t i s important t h a t a magnetic a r i t h m e t i c element be b u i l t and t e s t e d soon, for comparison w i t h tubes and t r a n s i s t o r s .

The J a c o b s Computer, b u i l t by the Jacobs Co. of Bal t imore, Mary­l a n d , has been descr ibed in glowing terms i n adver t i s ing l i t e r a t u r e — i f i t l i v e s up to t h e s e claims, i t s techniques should be worth looking i n t o .

R. C. Sims of Papian1 s group w i l l bui ld a small (say 5-step) m a g n e t i c stepping r e g i s t e r t o t r y to answer ques t ions on use of cores i n c o n t r o l — e s p e c i a l l y whether power can be got out of cores i n useful amounts.

Oils ' I M T D A I L

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Memorandum M-1511 ^ U^V« UvJ U U Lni IL p a g e 4

The new uncoated ca thode material developed by P h i l i p s Laborator ies a t Eindhoven (Netherlands) sounds qui te promising to extend tube l i f e — T a y l o r expects t o s e e one of t h e i r r ep re sen t a t i ve s soon.

De lay - l ine dynamic f l i p - f l o p s of the SEAC type, us ing 7AK7's, are t o b e invest igated by Dick B e s t , possibly a l so by Jacobs. These would have t h e v i r t u e of h a v i n g se l f -conta ined gates, could be connected i n a c i r c l e t o p r o v i d e 2 or more gates for a l t e r n a t e s t a t e s . (The ques t ion was asked, how about 10 for a decimal machine?) These would e i the r have t o be run w i t h synchronous p u l s e s or an r f c a r r i e r ; engineer ing cons idera t ions p rac ­t i c a l l y veto the l a t t e r . This i n v e s t i g a t i o n , i t was thought , i s more impor­t a n t than to pursue "low-performance" f l i p - f l o p s , p a r t i c u l a r l y i n view of a r e c e n t observat ion by R. R. E v e r e t t that a 50% speed inc rease i s a bargain i f o n e does not h a v e to pay more than a 2C$ i n c r e a s e in equipment for i t .

N. T a y l o r mentioned i n c i d e n t a l l y t h a t d i r ec t ion of the WWII block d i a g r a m s work w i l l be taken over by Everet t s h o r t l y , with probable changes i n organiza t ion and procedure.

The June 3 meeting, a l s o quite b r i e f , brought f o r t h only two i tems:

R. E v e r e t t , who was p r e s e n t , said he needed a week or t en days t o c o l l e c t his t hough t s on how the b lock diagram e f f o r t might proceed; in view of t h i s and the d e s i r e of o the rs i n the group t o devote themselves to some­what divergent p u r s u i t s , i t was agreed to suspend these meetings u n t i l f u r t h e r notice.

R. Mayer pointed out t h e p o s s i b i l i t y of building a " p a r a l l e l " mach ine in which t h e various d i g i t s are represen ted by presence or absence of c e r t a i n r-f f r equenc ies in a f requency-mult iplex spectrum. Such a t ech ­n i q u e would make p o s s i b l e s e l e c t i v e gating by u s i n g various l o c a l o s c i l l a t o r s to b e a t against t h e r-f , genera t ing various IF*s which would be guided to t h e i r des t ina t ions by proper band-pass f i l t e r s .

Everett commented t h a t t h e r e i s a fundamental f a l l a c y i n thinking t h a t such frequency -mult iplexing actual? v enab le s one to t r an smi t information f a s t e r than he o the rwi se could: wi th a given t u b e or analogous element, wh ich has a p r a c t i c a l upper f requency l i m i t , i t w i l l be necessary to have a p u l s e envelope o f cer tain minimum length t o a s su re adequate f i l t e r response to t h e various modulated c a r r i e r s . There i s no s ign i f i can t d i f ference b e t w e e n this enve lope length and the length of a t r a i n of narrow pulses (approximating one top-frequency c a r r i e r cycle) necessary t o code the same i n f o r m a t i o n in s e r i a l form.

Taylor commented f u r t h e r t h a t the f requencies necessary for such uses a re unfor tuna te ly t o o high for e a s y cons t ruc t ion of lumped-constant tuned c i r c u i t s ; that t h e a l t e r n a t i v e , namely, resonant cav i t i e s wi th waveguidj and c o a x i a l plumbing, i s horrible t o contemplate.

4& HK>__?1™ ~ C A \ w* A« Hosier

APPROVED FOR PUBLIC RELEASE. CASE 06-1104.