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REF ID:Al05~C'~­

D R A F T 

5th Memo In..:i. 

TO Chief Signal Officer 

THROUGH: War Plans and Training Di vision 

'Pfte cmdeI s:i'~ h~-, me4e ~ further st~dy of the s_ystem proposed ~~-Y.~..a in the original sketch accompanying basic memorandum..>\vith the result that 

an important madificati~~J~:f..~e~~ 

~~ therein which it iR believed)has 

eliminated the featurt ~ ~v£~~ .a&ou:& "TOld:eh Pe-tent--B.oard-~~~. -et:ftl"esseJ-·q-aesti-on ~ A 

a... to ~&Ot-ica~l~ This change provides that at-. no paint on the steel 

tape is there ever impressed more th~n one set of voice frequencies, the 

superimposition of sets of frequoncies being accomplished by electrical 

mixing in transformers rather than by successive magnetic impressions on 

the steel t~pe. A search has been made, at our own expense, in the 

Pa.t.e".lt 0ffice and there appear to be no conflicting issued patents dealing 

wi tn s3 e·ee111eos d' eh.H'M" means~ accomplishing the ,.purpose of this invention.> 

although the Radio Corporation of America and some other organization/ have 

o-1~ patented iif~epe1!!1; schemes for accomplishing a similar purpose. 

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~nde~- believ~that this modification eliminates tbe 

technical obje~~ons on which previous action of t,he Patent Board was based.'Sr~ 

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the Boar·~ ~ be asked, 

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reconsider 

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@'pp roved for Release by NSA on 09-11-2013 pursuantto E .0. 1352a 

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Transmitting end: Electrical oscillations corresponding to imput signals are recorded on a moving 

steel tape, the tape pass~ng in the direction shown between the paired impressing magnets 1. The tape 

then moves between pairedjreading magnets 2, 3, 4, and 5 which pick up the signals on the tape and pass .. them into modulating ampltfier 6. Thence the signals go through power amplifier to output. Thus, the ' 

final output corresponds re a sequence of blocks of algebraically superimposed frequencies representa~le 

by A, AB, .ABC, .ABCD, BODE, CDEF, ••• , the A block of frequencies coming at the head of the train. Except 

for t~e first.block, A, e~ch block of frequencies is-mixed with one to three blocks preceding it. 

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Receiving end: Received' signals are led to receiver and thence to transformer 7, which has three 

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coils. Signals from the iransformer 7 are impressed on steel tape by impressing magnets 11, and simultaneously led to amplifier 8, for final output. Signals on.the tape then pass under reading magnets 21, 

31, and 41, which feed into ampli~ier 9. Output of the amplifier 9 is reversed in polarity and led to 

transformer 7. When the block of frequencies represented by A is received, there is nothing on the tape 

.for reading magnets 21, 3f, and 4', to pick up. Hence A is fin-9.l output. When the block of frequencies 

represented by AB is received, reading magnets 21 are reading the A block, and these frequencies are led 

back to transformer 7 through amplifier 9. This neutralizes A from the received block AB, leaving only B. 

In the same way when ABC comes in, the re~ding magnets 21 and 3' feed back -A and -B, neutralizing the 

latter from z\BC and leaving only C; ••• etc. The cryptographic principle consists in micromctrically 

varying.the distances between the impressing and reading magnets at the two ends, the variations being . determined by prearranged cipher keys. While in this embodiment st.eel tapes o.nd magnetic recordings a.re 

used, other media may be employed for r~cording the basic principle being the mixing with the signals, 

recordings of signals which occurred during previous time intervals. I 

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