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Патент USA US2406347

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Aug, 27, 1946°
2,406,347
FQG. BUHRENDORF
SPEECH PRIVACY COMMUNICATION
Filed July 11, 1941
20R3:N
Quki
//v l/ENTOR
E6. BUHRE/VDORF
By
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,‘da
ATTORNEY
arcs?
Film
Patented Aug. 27, 1946
UNITED .s'm'rss ‘PATENT
‘SPEECH PRIVACY COMMIUNICATION
Frederick ‘G. Buhrendorf, Hastings on Hudson,
N. Y., assignor to Bell Telephone Laboratories,
Incorporated, New York, N. Y., a corporation of
New York
Application July 11, 1941, Serial No. 401,908
5 Claims. (Cl. 179—1.5)
-1
.2
H'VI'he present .rinventionrrelates‘to the use of ro
tary distributors .for subdividing messagerirwaves
the next should be made atlthe same instant and
on a time basis for transmission or ‘reception.
.More particularly the invention relates to .the
problem of coordinating the movements of a re
cording medium such as a magnetic tape and a
rotary distributor located at one point to the
movements of vsimilar apparatus at a distant
point.
_.'I‘he invention will :be disclosed, for illustra
tron, as embodied in a speech privacy system in
which speech is recorded on a moving magnetic
_
‘Moreover; if the
same "apparatus 'is to be used alternatively to
transmit and receive ‘for :purposes of two-way
V with minimum transition time.
conversation, the distributors must be capableof
serving for either transmitting or receiving-and
cannot be of different design.
It is ‘possible to secure some of ‘the advantage
of running-the receiving distributor slightly fast,
byiactually‘running it at the same constant speed
as ‘the transmitting distributor but delaying
slightly the sending out of the start‘impulse so
tape and ‘is subdivided on a time ‘oasis by a r0
tary distributor so arranged as to send out the
fragments of speech :in ‘abnormal sequence to ‘
that‘both distributors are normally stopped for
:me he reception‘by unauthorized persons difiicult.
tributor. This enables all distributors'to beialike
in construction, and when'any :distributor is con
A similar magnetic tape recorder and rotary dis
*tributor at the receiving point subdivide the re
ceived privacy vspeech and rearrange its parts
:into'understandable speech.
‘Various ways of synchronizing'the transmitting
and receiving distributors in sucha system have
been proposed heretofore. These have involved
rather complicated constructions or have, in the
case
the simpler constructions, been subject to ~
- dropping out certain small portions of the mes
sage waves under normal operating conditions
with introduction of some noise or distortion.
An ‘object of the present invention is to im
prove .upon suchiapparatus by providing a simple
construction which in normal operating condi
tion loses none of the message in the subdividing
process.
It is commonzipractice in printingitelegraphy to
.use start-stop distributors and to run the receiv
ing distributor normally slightly faster than the
transmitting distributor so {that normally it is
stopped ‘for a longer time, in each revolution,
than ‘the transmitting distributor. Errors in
speed of the receiving distributor result in vary
"ing the duration of stoppage‘of the (receiving dis
itributor, and by running the receiving distributor
normally too fast a greater margin is allowed in
stoppage time to compensate for speed varia
tions. If the receiving distributor varies in speed
by '1becoming still faster the stoppage period is
‘prolonged. If the variation is slowing down, the
stoppage time-isreduced. It-is customary in such
systems to make the receiving distributor seg
an interval to allow a time ‘margin in which to
correct for errors in speed of the receiving dis
verted ‘from receiving to transmitting it is ar
ranged automatically 'to send out the delayed
starting pulses. .All receiving distributors are
then synchronized to ‘the distributor that is at
the time transmitting.
The invention makes use of the “delayed start
ing pulse but avoids'the attendant loss of a small
percentage of ‘the speech 'Which ‘has been experi
enced with ‘the delayed impulse method. ‘While
‘the delayed starting impulse allows a time mar‘
gin for purposes of synchronizing the start-stop
distributors, there remains theproblem of ?tting
the distributor movements to the motion ‘of the
recording tape. The message is recorded con
tinuously throughout ‘its duration which has “no
necessary relation‘tothe distributor operate‘time,
vand the tape moves continuously. What is de
sired of the distributor is to enable equal "lengths
of the ‘record as measured along the tape to ‘be
reproduced in any order in accordance with the
particular code and to repeat such reproduc
tions ‘inde?nitely without loss of any part of the
message.
‘This is accomplished in accordance ‘with one
feature o'f'the'invention by'making one distribu
‘tor segment shorter than the others by such
amount that the travel time across such segment
plus the stoppage or waiting time is equalto the
travel time across each o'fthe other segments.
'The nature of the invention and its objects
and features will be more fully understood from
the following detailed description and the accom
:ments shorter than the transmitter segments so 50 panying drawing.
;as<to1pick out ‘the middle part of the transmitted
pulse.
‘In the drawing,
‘Fig. 1 is a schematic circuit diagram of ‘a sys
distributors are used to ‘subdivide the message
tem of speech privacy incorporating the inven
tion, and
waves as referred to above, start-stop distribu
tors may also be used'but‘the synchronizing pre
of the tape and recording and reproducing mag
sents a much ‘more diiiicult ‘problem since it is
nets to show their spacings, and of the com
mutator to show the use ‘of a, short segment in
‘In a speech privacy system in which rotary
necessary to preserve as far as possible the en
tire wave, which means that ideally each transi
tion‘of‘the two distributors from one segment to
‘Figs. 2 and 3 are diagram views respectively
accordance‘with the invention.
Referring to Fig. l, a constant speed motor
2,406,347
3
III of suitable type drives a shaft II which is
shown as driving magnetic tape I2 mounted on
the rim of a suitable disc, brush arm I 3 rotatable
over the segments of commutator 29, and a gear
train I4, I5 driving a contact making cam [5.
The system is arranged to transmit with privacy
when speech is spoken into the transmitter’ I'I,
4
to the other segments.
In this way it is ar
ranged that the currents transmitted through
coil 3| represent fragments of the recorded speech
picked up in a sequence different from the se
quence in which they were recorded. Moreover,
this sequence is varied from time to time by
changing the settings of the code switches 38.
This general method of transmitting fragments
of speech out of their normal sequence and of
under certain circuit conditions to be described,
and to receive with privacy in receiver I8. The
transmission and reception of the privacy Waves 10 changing the code is more fully disclosed in a
takes place over the line 22 shown interconnect
copending application of J. C. Steinberg, Serial
ing the terminals in Figs. 1 and 2.
No. 401,897, ?led July 11, 1941, which may be
A number of two-position switches are illus
consulted for further details including the con
trated at 23, 24, 25, 21, 54 and 55. These switches
struction of the code switch mechanism 38.
may, if preferred, be ganged together or they 15
The speech waves occurring out of their nor
may be in the form of relays operated by a single
malorder in coil 3I are transmitted through
push button. These switches are all assumed to
switches 25 and 24 and ampli?er 36 to the‘ out
be operated to their upper positions in the ?gure
going line 22.
1
(and switch 2'! to the right) when speech is to be
Attention will now be given to the start-stop
transmitted and to be operated to their lower 20 mechanism to which the invention particularly
or opposite position when speech is to be received.
relates. The brush arm I3 frictionally engages
Such switches are commonly referred to as push
the shaft I I by suitable friction clutch mechanism
to-talk switches and may conveniently be re~
so that when the brush is released by latch 32 it
tracted to their receiving positions by springs
rotates with the shaft II but can be held sta
(not shown), the receiving position in such case 25 tionary by latch 32 while shaft II continues to
being considered normal. The circuit of Fig. 1
rotate. Latch 32 is released‘ by tripping magnet
will ?rst be described for the transmitting con
33 when energized from tube 50 under control
dition, so that'switches 23 to 21, 54 and 55 are
of cam I6 and contacts 34 and 35 when, the sta
considered thrown to their upper or talking posi
tion is transmitting or under the control of sim
tions.
30 ilar impulses received over the line from a distant
The tape I2 is assumed to be rotating in a
station through coil 46 and ?lter 60 when the
clockwise direction at constant speed. Located
station shown is receiving.
around the periphery of the tape are an erasing
The gear train I4, I5 drives the cam I6 at a
magnet 2| supplied continuously with current
slightly slower rotational speed than shaft II.
from the battery shown, a recording magnet I9
and nine reproducer magnets 20 located at equal
intervals around the tape. When speech is spo
ken into transmitter I'I, therefore, the speech is
For, example, the gear I4 may have seventy-four
teeth and the gear I5 seventy-?ve teeth. This
feature is disclosed and claimed in the copending
recorded on the tape at I9 and the recorded por
tions in passing the magnets 20 generate corre
?led Oct. 8, 1941.
application of W. A. MacNair, Serial No. 414,054,
,
Assuming that the’ arm I3 is stopped against
sponding electromotive forces in their windings.
latch 32 and that the cam I6 is about to move’
The terminals of these windings are connected
the contact spring upward to close contact 35,
this contact will, then, be closed and connect
condenser 48 through upper contact of spring 54
through code switches 38, ?ve in number, and
thence through contacts of switch 2‘! to the seg
ments of commutator ring 29, which are num
across inductance 49. The condenser, which has
bered in order I, 2, 3, 4, 5 over one-half of the
circumference, with these numbers repeated in
the second half of the circumference;diametri
previously been charged to the full potential of
battery 47 through contact 34, now discharges
suddenly through the inductance 49, causing a
highly damped'wave of 2,000 cycles per second
frequency to be generated in the ?lter 60. One
series tuned branch‘ 6| of the ?lter transfers
some of this 2,000-cycle voltage to the input of
tube 36 across resistor 64, and the other series
cally opposite segments being directly connected
together.
The code switches are so arranged
that, one winding terminal of reproducers 20 may
be connected in a number of different sequences
to the commutator segments of ring 29. Brush
arm I3 carries brushes bridging across fromseg
mented ring 29 to solid ring 30, the latter being
‘connected to one terminal of winding of speech
coil 3|, the opposite terminal being common to
(233m terminal of each of the reproducer magnets
tuned branch 62 transfers some of the 2,000-cycle
voltage to the input of tube 50 the grid circuit
being connected across the inductance 63. On
the ?rst positive swing of this pulse wave, tube
50 breaks down and sends a fairly heavy current
through release magnet 33, releasing the brush‘
It will be seen, therefore, that as the brush 60 I3. At the same time, the brush at the distant
arm I3 rotates and sweeps the brush over the
station is released by the pulse sent over the line.
segments of the commutator, different repro
At the end of the pulse the tube 50 is restored
ducers 20 are connected to the speech coil 3| in
by the aid of plate'circuit condensers‘65 in com
sequence, and the particular sequence is at any
bination with the rest of the circuitelements.
given time determined by the setting of the code
Since the apparatus at station 2 is aduplicate
switches 38. For example, designating the‘re
of that at station I, the action‘ taking place in
producers 20 beginning next to the recording
station 2 in receiving the waves sent out from
magnet I9 and continuing around the periphery
station I in accordance with the foregoing de
of the tape as reproducers a, b, c, . . . i, repro
scription can be understood by considering that
ducer a may, with one code setting be connected 70 similar waves are being received in station I in
to commutator segment I, reproducer 0 may be
which case all of the two-position switches 23, 24,
connected to segment 2, reproducer e may be
25, 21, 54 and 55 are assumed in their lower or
connected to segment 3, etc. With a different
receiving position.
setting of the code switches 38 reproducer d might
Considering ?rst the start impulse sent out
be connected to segment I, and other reproducers
from station 2, this is received through trans,
2,406,347
5
‘ former 4'46, lower contact of spring $55 to input
iterminals of ?lter 60. ‘It will be notedthat con
denser'll8 is now ‘ in parallel with inductance :49
and forms-part of the ?lter to separate the start
pulse wave from ‘the speech waves. ‘The~2,()00
- cycle ‘frequencywave is applied to'thev grid of-tube
50 and the ?rst 'positi-ve swing renders the tube
conducting, sending a large pulse ‘of current to
6
altered ‘sequence, this long speech fragment may
occur as the last recorded fragment, orimore gen
erally, depending on the codecombination in use,
the material recorded at the receiver in the last
(long) interval will‘be a normal length fragment
plus a small portion of another fragment out of
its normal sequence, and this material is what
is received in the ?nal or long interval. This
the winding’ of the tripping magnet-‘33 releasing
extra amount .or left-over material appears,
brush is. As long as the station in Fig. ‘2 con 10 therefore, as noise, and the corresponding small
portion :of .theilong speech fragment is dropped
tinues *to transmit, the cam 16 at such‘ station
sends out astart impulse once each revolution ‘of
- out.
.This effect is avoided by making the seg
the cam, which .as stated rotates vat a slightly
ment on which the brush isistoppedshorter by a
lower ‘speed than ‘the distributor shaft. ‘This
suitable amount than the other segments.
causesthe‘brush arm 13 at stationlz to‘be stopped
Reference‘is made .to Figs. 2 and 3 foranun
momentarily ‘once each revolution. The brush
derstanding of how the length .of the short. seg
arm l3 at station I, serving-as the receiving sta
ment may ibe properly determined in any case.
tion, if running vin exact synchronism is stopped
These ?gures are based on Lthe .assumption that
once .each revolution for the same length of time
a ?ve-unit code is'being used, althoughany other
as the ‘transmittingcommutator brushor, if the 20 number of-time divisions, such as six, seven,ietc.,
‘receivingibrus‘h is'running slow-'or‘fastiby a slight
could‘as wellbe ‘used, in which case instead of-the
amount, it .is stopped for a shorter or longer
ten segments shown-there wouldibe 12, .14, etc. In
length of time as the caselmay‘ be.
interpreting the formulas given below the num
The jumbled‘speech waves received‘from sta
ber 10 should be-considered-as illustrative of‘the
1tion 2 through‘ switches 124 and 23 energize ‘the
?ve-unit case andnot asilimiting.
winding of/recordingzmagnet £9 to make a record
of the received waves on the tape I2. As this
In Fig. 12 ‘a plan view, or view in diagram, is
given of thetape "[2 on the rim of the tape‘disc,
tape rotates past the various .reproducer magnets
1253, these latter ‘pickup the recorded wavesand
and of the nine reproducer magnetszil, recording
magnet l‘91anderaser magnet‘zl. The ‘angular
distance between pole-pieces of magnets '29 is Dr,
and the angular separation of the last reproducer
‘transmitlth‘em through code switc'hiiil :and switch
'21 ltothe segmentsiof commutator 29 and the wir
ing and settings of ‘the .code switches are such
that as the .brush lt'passes over the commutator
segments in successionthe speech'fragments tare
rearranged in their normal order in the 1coili3l,
from which ‘they are .transmitted'through switch
zitoireceiver I58. Wh'enithe code switches?a ‘and
.the wiring are 'made in ‘accordance‘with ‘the dis
closure 10f :the Steinberg .‘appli'cation above .re
ferred to, a given ‘setting .‘of :the ‘knobs '28 'will 40
result in transmitting in accordance witha par
'20 from the ‘recorder 19 is 1D2.
The eraser is
shown fha'l'f way along D2, ‘although ‘this spacing
is not especially signi?cant.
In Fig. '3 the commutator i2'9 is composed of
ninesegments of angularlengthTLra-nd one short
segment of angular length lLz, the latter being‘the
segment ‘on which-the brush 113 is stopped. The
di?erence in length of 1L1 ‘and L2 is exaggerated
in this ?gure for illustration.
If the tape disc and commutator arm arelboth
ticular .code :and .a soinrreceiving in accordance
mounted on ‘the same v‘shaft II as in ‘Fig. ‘1, ‘they
with the same code. 'The knobs '28 in Figs. 1 and
have the same angular velocity S when rotating.
2 are, therefore, given the same setting.
There is no necessity that they ‘should‘have the
The ideal timing relationsare-such that a given 1.. same *angular velocity since either or both may
point on the tape passes the successive repro
be driven through gearing. If it is assumed for
ducer magnets at the same instants that the
generality that the velocity in degrees per sec
brush passes from one commutator segment to
0nd of the brush is S, while that of the tape is S2
the next and that these occur at equal intervals
EiL_1_1_QQ1_
and at the same instants at transmitter and
S1 _ S2 _
receiver. Where the tape is running continu
ously and a continuous record is being made, a
where T is the time between start pulses in sec
stoppage of the brush is immaterial so long as it
onds.
passes off one segment and on to the next seg
Considering revolutions per second, if
ment at the right instant. If there is to be stop
V1=R. P. S. of the brush arm shaft
page of the brush, it must be required to travel
V2=R. P. S. of the tape drum shaft
less distance during its moving time since the
V3=R. P. S. of the cam shaft driving cam l6
brush when moving‘ is running at constant speed
(except for acceleration time) for otherwise it
could not reach the end of the segment in time. so
By making the segment on which the brush is
stopped slightly shorter than the other segments,
the stoppage time plus travel time over that seg
ment can be made equal to the travel time over
the other segments. ‘The stoppage allows the 65
brushes to he started in the proper timing despite
small errors in rotational speed.
If the segment on which the brush is stopped
has the same length as the other segments, the
brush is on that segment for a longer total time
than it is on any of the other segments, which
In a practical case
L, Q
—‘STI<SI+.OO5 sec.
where an allowance of .005 second is made to in
sure that the brush comes to absolute rest when
means that the length of tape passing the cor
the latch is operated and to allow the brush to
responding reproducer magnet is longer than in
come up to speed.
the other time units. When the speech frag
The details may be varied to suit various con
ments are sent and recorded at the receiver in 75 ditions of requirements without departing from
2,406,347
8
7
the invention, the scope of which is de?ned in the
’ ing of such length that the duration of closure of
a claims which follow.
What is claimed is:
1. In a start-stop distributor, a plurality of
equal length segments, a brush rotating over said
segments, an additional segment shorter than
said ?rst-mentioned segments, means to stop the
brush on said short segment, means to release the
brush to start on its next revolution, means to
the circuit connected to said short segment is
equal to the duration of closure of each of-the cir
cuits connected to said other segments.
,
4. In a speech privacy system, the combination
with a magnetic tape, a recording magnet and a
plurality of reproducer magnets spaced along said
tape, a reproducer circuit and means including a
start-stop rotary distributor for selectively conproduce a start impulse to operate said release 10 necting said reproducers to said reproducer cir
cuit in sequence, said rotary distributor compris
means, and means to time said impulse to cause
ing a segmented ring and a brush movable over
the total travel time plus rest time of the brush
said ring, a start segment, and means to stop the
on said short segment tobe the same as the travel
brush periodically on said start segment, of means
time across one of said equal length segments.
for transmitting to said circuit the same length
2. In a speech privacy system comprising inde
of recorded speech on said tape from each repro
pendently driven continuously moving record
ducer magnet comprising a shorter length of start
media at transmitting and receiving stations,
segment than other segments on said distributor,
means to record speech on the record medium at
the di?erence in length thereof with respect to
the transmitting station, means to record re
the other segments on the distributor being equal
ceived privacy waves on the record medium at the
to the distance of travel of the brush in a time
receiving station, rotary distributors at said sta
equal to the normal period of stoppage of the
tions comprising segments and brushes rotatable
brush on said short segment.
‘
over said segments, a plurality of reproducers for
5. In a speech privacy system, the combina
each record medium connected individually to
tion with a magnetic tape recorder, a plurality of
segments of the corresponding distributor, start
reproducers spaced along said tape, a reproducer
stop mechanism for each distributor, means to
circuit, a rotary distributor having a segmented
start said distributors in step with each other and
to stop them on a given segment at the end of a
revolution, said segment being of such length that
the travel time of the brush over such segment
ring and brush movable relative thereto to con
nect said reproducers in sequence to said repro
ducer circuit, a common driving means for mov
ing said tape past said reproducers and for ro
tating said distributor, of means for insuring
equal time intervals of connection of said repro
ducers to said reproducer circuit comprising a
short stop segment for said distributor, saidseg
ment serving also to connect one of said repro
currents in equal time intervals, a ring of con- ducers to said reproducer circuit, means to stop
ducting segments including a plurality of equal
said brush on said short segment and to restart
length segments and one short segment, a circuit
the brush, the difference in length of said short
connected to each segment, a common circuit
closing means for sweeping over said segments 4.0 segment from the other segments being equal to
the distance of travel of the brush, at its normal
and closing each of said circuits in rotation,
rate of travel, in a time equal to the time of stop
means to stop said common circuit-closing means
page of the brush on said short segment.
on the short segment, and means to start said
plus the stoppage interval thereon is substantially
equal to the travel time of the brush over each
of the other segments When the distributors are
rotating at correct speed.
i
3. In a start-stop distributor for transmitting 35
common circuit-closing means on its next rota
tion over said segments, said short segment be
FREDERICK G. BUHRENDORF.
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