LETTER TO BOB FROM JOHN RE INFORMATION OF IMPORTANCE TO SOME OTHER STATIONS

• Document Type: FOIA
• Collection: FOIA Collection
• Document Number (FOIA) /ESDN (CREST): 0005309844
• Release Decision: RIFPUB
• Original Classification: U
• Document Page Count: 3
• Document Creation Date: June 23, 2015
• Document Release Date: August 27, 2009
• Case Number: F-2008-01895
• Publication Date: September 9, 1945

Dear Bob., gept 0
Here is some info oln_ a.. subject .bout vihich-:~you nay_- not. be awrware
and v?hich to any event is not ! believe of great imprtance to you.
It is of imprt ante . to_ J,%// some other stations for /W_ reasons
which you will see as we go along so I think we should all be
fan, ilia.r with it.
All electrical equipment such as -teletype machines, TOTs, tl_'s, some switchboards, the SIGCUI:I the 1700 and so on give out
types of radio waves vihen?'iZe,r they are operated. Of caul~se __-in
variuos T
the case of many of these machines the radio ivaves are small in
power~~~ ~> ~1~ ,~f and so-dinto very far. `'hen -again - if there -are-
a lot of therm. going; at once they inteffere/ with each other and
no recognizable signal can be picked up. Then -again even if `the
signal that is -oven- out carries for some-. distance the situation may
be such, as for instance at Caserta, where- we had meads of knowing
whether there were people around within the distance of
daneger setting up rec?rdin equipment. (I thins, tho that ''as erta
as a bad example to give on~ that score as the recording apparatus
is not large -and could possibly have beeh set up in t? e woods up
the hill without discovery.
as you can see there ar. e a lot- of factors which may
_-,__--
prevent any danger as a practical matter arising regardless of
the pact that plaintext sign ls_ maybe
rivenout. l'\o_t__all_the
above instruments. give out plain text. it all depends at what points
in the coding process < ny arcing or _sparks occur Fo '_ ins t.ance,
in the case of the TKa the decode process produces a strong,
I.airt text signal whereas in encode there:-is na-_.r-eco-4 ni-sa.?le
.
s i-nal unless the plaintext tape is cut independelty of the coding
process
For your info 1 will list -the various instruments that 1
know of and the nature of the signals they give out:
ABA, u.?, L2HA, 1700 -~ only operant g signals (-,-hat
is neither plain nor cipher radio laves, dust
a routine signal that is the same for every
turnover of the machine..)
SIt-.:CUI;I -s A considerable plainted V signal (r.1ore oil
this later.)
TOT - cipher text signals are radiated. In addition.
if the relay which is used for remote control
as in con en, ence rvorl17 is used _a s ror_`,, p in__ text
s ig_;nal is emitted.
TK - see above. The plain text signal is nixed with
certain operating signals but is_ distnigu.i-skiable.
RTP,'IED - Only operating signals
APPROVED FOR RELEASE^
DATE: 19-Aug-2009
 SWITCHBOARDS - No tests made in most cases. The BD~100
plain--or cipher-__t_el t.?
gives a strong signal duplicating whatever is put thru
mom? TYR - -I-t- is a----f act-that---al 1.---t
(if not surpressed) give out a creak to medium signal
- wig ch duel c> a ~ -whatever---a s be .n~ t e.d4 (she.
Western Union teletypes give a much stronger signal
-than- the----Ielet-yTJe--Corp--)- - - - - - - - - -
How strong are these signals? Well they range up to about
th riaximum (TK decode, 3D --3-00) of 400--rr! crovC~~ ts- per--meter _ ___n ___-__ _-___.
which means that unr favorable -conditions the signal could be
heard_ wlt"ri- relatively- sirple; pti tabJ e e pxipeirtn: any recorelad at - - -
a distance of 20 to 25 yards.
An exception is the SIGCUT which it is claimed by the Bell
Lab laeople altho~c i~^re made r~~ ne is nurselvos can be heard_ at__
great distances. (Again more later on this.)
a3oUp_,i-ote---that these radio type sI,,T,nals are of no espeial
wave lengths but rather of all,wave lengths although any species-1____
have its own frequency ora number of them at which
it can be, heard better.
Note this too. That in every, case it. is possible to surpress
the- signal by a pxoprt-e--z-s-e- of -sur--r--ss.ors ~_{c:.ondens_ess..3 ._shiel_di:n:g~.:._._- --.
of the wires and so on. You have to have a competenet radio tech
nit-ian =:.hough.--to do--th s--and-sin o the ~vave^..:are +.a_ven_:_nut.:.at_. n:1----._._~.__
and all frequencies he has to.. actually test the whole 'damn
spe-c-trum f-rorrr--top--to-bottom-- Land -practically into--sou-nd__v ave- _fre -____
quency. The Bell people told us how they thought they had worked
out- surp~~ess~ on---- .or---on - machine _a:nd-tl eta--fou d---oF e-- sin l-e--set-of------
waves ,-,et Ling gray which would have spoiled the whole thin;.
------------
Not only v M the use of proer suppressors and so on fix
any -fl iacl11 bUt a1 o tl e: us c ei tad 1?o ',? f _. _ p.r-oof cage wr11 - -
work fine if all thr, wires that run out have traps on them. We
actzaTlyul~z 6n e or -out tIC si.~id c tao?k-e.___7 ke a c-harm:--but-_we_
had to run around and test it very carefully first because one wire
lIa.c i roc t _~e care a iri l unaa
run:zin ; out of the
all -Tour Vlorl?C.
any wires
tlzat~
the frequencies involved have a Beat af'init for
You will noticre i spoke of the importance of wires. Some of
rz_:_tkio_z eor~-_ and,_ tv :] 1_. ;et dt t o the wirea n d t run ciown the,? for__-_-------
great distances. Further they will radiate from the wires so that
tine e an tae p -cl~-ed_ up by i abu.ct on f _o~ ear~_._the e r s ._ l at9Li _ the
problem with the SIGCUTMMM because the well people insisted that
_-- 1.-aa-in:t e: ----r- an r -ght-4c wn-the- ~ _ix.-e_a1.on it? t~ h ?b.es_. t~~ _ aut` - -
that the timing: was such that you could keep them separate from
each ether irr tl e recording and so---r;eaa the --t:ra.it=%c-a- nuabe of
miles, froi;i the origination point. I. no not find the Army is very
- -e c. a t-e ct- ab a t--thi-s--p.01 n n_ _o ?__~;h~ __-_CtT _u-t -ara ? i l r e d t o -be 1 ?eve
 the All people over the Army because some of the young officers
who had been working on this at ?rl~ n toz tjere ~..orried and- becaudM
Bell doesnt say- it -can CO a thing If it cant.
it man the Wires in the case of the `fN that were the real
danger. Completely unsurpressed we could hear the plaintext not
much r_1oro than 10 or 15 f eet.outside of. our base sent, on the road
But the signal got onto the telephone wires and ` ran i' down them so
the= t you could -hear- very plainly up by "entr_al and North buildings.
and presumably considerably further even .w e?~ e taking the
fu. t'~ ..tQu;0 r2 we, t;~; ty~?
signals off by-Induct ion.. t.-r_ poi-nt perha >s--sixt_o 10 feet _. rom
the wires themselves.
The point in all this is not so much hat there is a serious
danger in -every station-but rather --t"t;- c;here i__s a-posibility
of danger the extent of which must be realised in order to
determine-zhother anything need be Mae; if something is to
be done we have no one to cope with it ourselves and have to call
in a radio r
c'senrcti man to 'ie pp
;3ob, All teletyp . "Corp teletypes