US2217157A - Telefacsimile transmission system - Google Patents

Description

A. G. COOLEY TELEFACSIMILE TRANSMISSION SYSTEM Filed March 25, 1958 Sv-Shqets-Sheet 2 l INVENTOR ATTORN Y Oct. 8, 1940.`

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TELEFACSIMILE TRANSMISSION SYSTEM Filed March 25, 1958A- .Oct. 8, 1940.

INVEB'AS? BY fd/f ATTORNEY Patented Oct. 8, 1940 PATENT OFFICE TELEFACSIMILE TRANSMISSION SYSTEM Austin G. Cooley, New York, N. Y., assignor to Wide World Photos, Inc., New York, N. Y., a corporation of New York Application March 25, 1938, Serial No. 197,991

9 Claims. y (Cl. 1785.6)

This invention relates to telefacsimile transmission and more especially to systems for transmitting facsimiles between widely separated localities, employing existing telephone, telegraph "10 phone wire channel; and also transmitting from the same source to one or more distant receiving points over a carrier telephone channel.

Another object is to provide a system of telefacsimile transmission from an originating source 5 over existing telephone service lines, to a plurality of distant receiving points some of which are linked to the transmitting source via noncarrier lines, and others of which are linked to the said source via carrier lines.

Another object is to provideA an improved repeater arrangement for telefacsimile transmission over existing telephone service lines, whereby the transmission can be effected from an originating point by a non-carrier wireline to a main re- ,25 peating point and from which latter point transmission may be repeated over either'non-carrier wire lines or carrier wire lines to distant receiving points, without duplicating separate or complicated synchronizing equipment at each point. A feature of the invention relates to a repeating arrangement for telefacsimile transmission over existing telephone service lines, whereby compensation for frequency drift or other form of distortion introduced by a carrier link, can be v indicated and eiected at a central point. This enables the facsimile signals to be faithfully reproduced at a plurality of distant receiving points, notwithstanding that the signals during transmission have passed over a non-carrier wire channel and over a carrier wire channel.

Another feature relates to an improved form of drift indicator to compensate for frequency' 55 plished by delaying the repeating of the signals fromthe more expensive toll connected stations until the other tollconnections have been fully completed, and the called subscriber has answered the telephone.

A still further feature relates to the novel or- ,-5 ganization, arrangement and interconnection of parts constituting an economical and exible repeating arrangement for telefacsimile transmission.

Other features and advantages not specifically 1,10 enumerated will be apparent after a consideration of the following detailed descriptions and the appended claims. n

Since the invention is concerned primarily with a telepicture transmission and a repeating system J5 as a whole, only those parts of the system as are necessary to a full understanding of the invention are described and illustrated in detail. The details of apparatus which are well known'vin the art are omitted for the sake of clarity and in order 20 to enable the invention to be more readily understood. It is understood therefore, that wherever in the specication and drawings a device or apparatus is illustrated schematically in block diagram form, that any suitable apparatus well 25 known to the art may be employed.v Accordingly, in the drawings, p

Fig. 1 is a schematic block diagram showing the invention applied to a typical existing telephone service network. 30

Fig. 2 is a more detailed diagram of part of the system of Fig. 1.

Fig. 3 is a schematic block diagram of a modification of the invention. Y

Fig. 4 is a detailed diagram of the drift cor 35 rector and indicator arrangement that may be used in the system of Fig. 3. f

Where telefacsimile signals are to be transmitted from an originating source to a plurality of receiving points, over existing telephone servv4.0 ice lines, it frequently happens that one or more receiving points are linked to the originating` points by a carrier channel, and other receiving points are linked to the transmitting point by a non-carrier channel. As pointed out in Patent I15 No. 2,138,398, the characteristics of the usual carrier terminal equipment are such that upon demodulation of the modulated carrier, a frequency drift distortion may be introduced. Consequently, where the synchronizing signal is transmitted over the same channel as the facsimile signal proper, the receiving equipment Amay run out of step with the transmitter. This is especially so where the picture signal is transmitted in the form of a modulated pulsating or alternating current of fixed fundamental frequency which frequency is used for synchronizing, as described for example in Patent No. 2,045,294, granted to Austin G. Cooley. In accordance with the present invention, the frequency drift correction is effected at a central or intermediate point in the system, and a special form of indicator is used tovindicate when correction is required.v

Furthermore, when facsimile transmission is effected by employing the usual telephone sube scribers calling and answering equipment, and the transmission is to be effected tov va plurality of receiving points, one or more of the called points may be slow to answer the telephone call and if the transmission has been started, the slow-to-answer subscriber will receive only part of the transmission. Or if transmission has not been started, it may require that other expensivetoll connections must be held up until the slowt'o-answer subscriberremoves his receiver to complete -the connection. As an example, assume that a picture is to be transmitted from Boston to New York and thence repeated to Philadelphia and Toronto. It is quite obvious that when the Boston subscriber makes his call to the New York subscriber, and the latter is informed thatY the picture is'to be repeated to Philadelphia and Toronto, the New York subscriber thereupon calls the Philadelphia and Toronto subscribers. Consequently, even though the New York subscriber is in readiness to receive and repeat the picture signals, he must await the answer of the telephone bythe Philadelphia and Toronto subscribers respectively. Should both the Philadelphia and Toronto subscribers answer their calls simultaneously, then of course the transmission can be effected from Boston to NewYork and thence repeated to Philadelphia and Toronto. Should however, the Toronto subscriber be slow in answering his telephone or should the toll connection to Toronto be delayed, it is necessary to hold up the previously completed telephone connections until the Toronto subscriber answers his telephone. In the case of long toll connections, the holding timevof the previously completed trunk connections during this preliminary setting up of the connections' may constitute avery expensive procedure. In accordance with the present invention, this disadvantage is overcome by receiving the picture and recording it in the usual way at the New York station 'and Vrepeating it simultaneously to thefnearby'station, but delaying the transmission to those stations where the completion of the toll connection is likely to be delayed. l

Referring to Fig. -1, there is shown diagrammatically a typical set up of telephone lines for effecting facsimile transmission, it being assumed that the picture is to be transmitted from Boston to the various points designated. Each of the dotted rectangles of Fig. vl represents a telephone 'subscribers station in the particular locality designated. It is assumed that the telephone connection from Boston to New York is over a lnon-carrier wire line, while the connection from New York to San Francisco is over a carrier telephone line. In the drawings, the wire or non-carrier telephone channels connecting the various localities are indicated by the full lines whereas the carrier telephone channels are indicated by the dot-dash lines. The pictureto be transmitted is 'analyzedand translated into a series of current impulses by anywell-known apparatus designated` by the numeral I." For a detailed ldescription of such apparatus, reference may be had to Patent No. 1,593,651, granted to Austin G. Cooley. Preferably, the apparatus I is of such a character that the picture signals are transmitted in the form of an alternating or pulsating -current having a definite fundamental telephone frequency which is modulated in accordance with the shade characteristics of the successive analyzed elemental areas of the picture. For example, the fundamental frequency may be 1800 cycles per second, and this 1800 cycle component can be used as the synchronizing control signal. The picture modulated current is then applied to the telephone line 2 in any Well-known manner. Preferably, although not necessarily, the application is effected in the manner described in detail in application Serial No. 103,506, led October l, 1936, so that in effecting connection between Boston and New York, all that the Boston subscriber has to do is to remove his telephone receiver from its switch hook and ask the telephone operator to connect lhis line with the particular line in New York over which the transmission is to be effected.

`.The New York subscriber is provided with a photographic recorder 3 and also with a phonographic recorder 4. Associated with the recorder v4 is a phonographic repeater 5 by means of which the retransmission over the line 6 to the Toronto subscriber may be delayed. The Toronto subscriber is of course provided with a photographic recorder I which may be similar to the recorder 3.

The New York subscriber is also provided with a repeater 8 preferably, although not necessarily, of the type disclosed in application Serial No. 149,868, filed June 23, 1937. This repeater has a plurality of output coupling members by means of which the repeated currents may be applied to the respective telephone lines leading to the Philadelphia, Miami, Nashville, etc. subscribers each of these latter subscribers being provided with a photographic recorder I3, I4, I5, etc. similar to recorders 3 and 'I. At the New York subscribers station, there is also provided a phonographic repeater 9 by means of which the phonographic record produced on recorder 4 may be translated back into the corresponding picture currents. The output of repeater 9 is coupled, preferably, although not necessarily, as described in said application Serial No. 149,848, to the carrier telephone line leading to the San Francisco subscribers station.4 The repeater 9 is preferably driven by a synchronous motor I0 which is operated from a suitable tuning fork oscillator II. The fork oscillator is of such frequency that it causes the motor I0 to operate the drum or table of-repeater 9 so that the wax disc or the wax cylinder on the repeater 9 on which the picture currents have been recorded, makes one complete revolution for each 2400 fork impulses, it being understood that the picture drum of the transmitter I at the Boston station is also driven so that it makes one complete revolution for each 2400 impulses of the picture current. In other words, the current in the output of repeater 9 consists cf a fundamental frequency of 1800 cycles per second modulated in accordance with the shade characteristics of the original picture at Boston. At the San Francisco subscribers station, there is provided a photographic recorder I2, which may be similar to the recorders 3, lI, I3, I4 and I5. The recorder I2 is preferably driven in synchronism with the repeater 9 by means of a tuning fork controlled oscillator I6 similar to the oscillator II. A portion of the 1800 cycle picture currents received at the San Francisco ter that transmission is to be recorded at New l York and repeated to Philadelphia, Miami, Nashville and Toronto. The New York subscriber while maintaining the original connection with Boston then calls 'the subscribers at the designated points and when the telephone connections have been completed, a suitable signal is transmitted to the Boston subscriber, whereupon the apparatus I is set in operation and transmits the ypicture currents to the New York subscriberY where they are photographically recorded on the recorder 3 and phonographically recorded on the recorder 4. A portion of these picture currents are also repeated immediately by repeater 8 over the several telephone lines to Philadelphia, Miami and Nashville. Assuming that it takes a longer time to effect the telephone connection to the Toronto subscriber than it does to the Philadelphia subscriber, the phonographic repeater 5 is operated in time displaced relation with respect to the phonographic recorder 4 andthis time displacement may be Variable so as to allow the Toronto sub-scriber to come in on the connection without losing any of the transmission. When the transmission over the wire telephone lines has been completed, the phonographic record is removed from the recorder 4 and mounted on another phonographic repeater 9 which may be similar to the repeater 5, with this diiference however, that repeater 5 is mechanically connected to run at the same speed as recorder 4, whereas, repeater 9 is operated at a speed determined by the tuning fork controlled oscillator II-. The New York subscriber having placed and completed the toll connection to the San Francisco subscriber sets the repeater 9 in operation and the picture currents are transmitted over the carrier telephone line to the San Francisco central oice where they are demodulated by the usual central ofce carrier telephone demodulating equipment and the San Francisco subscriber therefore receives a current having an approximate 1800 cycle fundamental frequency and with modulations corresponding to the shade characteristics of the original picture transmitted from Boston. The photographic reproducer I2 is driven in synchronism with the repeater 9 under control of the local tuning fork oscillator I6 so that the drum of recorder I2 makes one complete revolution for each 2400 impulses of the received picture current. The fork oscillator I6 which controls the recorder i2 also acts as a source of carrier current for retransmission of the picture signals to the Los Angeles subscriber. For this purpose, a portion of the currents received by the San Francisco subscriber are detected by the detector I'l and modulate the current from the fork oscillator and the modulated output from modulator i8 is applied to the wire telephone line leading to the Los Angeles subscribers station. At the latter station, there is providedv a photographic recorder I9 similar to the recorder 3. Consequently, the recorder I9 'can be operated in synchronism`with the rtransmitter I and the synchronism can be effected over the wire channels by the fundamental frequency of the picture currents themselves, While over the carrier channel portion of the connection the synchronism is effected by the fork controlled oscillators. Referring to Fig. 2, there is shown in somewhat more detail the important parts of the equipment at the Boston, New York Aand San Francisco subscribers stations referred to in the set up of Fig. 1. At the Boston station, the picture to be transmitted is wrapped around the scanning drum 25 which is driven through suitable gearing 26 from a non-synchronous motor 2l, motor 27 also drives the toothed wheel 28 of an induction generator, which rotates adjacent a coil 29 and by means of which a current of 1800 cycles per second is generated in the circuit including coil 29, transformer Winding 30 and battery 3 I.

The secondary winding 32 is connected in circuit with the photoelectric cell 33, resistance 34 and battery 3`5. Light from a suitable steady source 36 is projected through condensing lens 31 on to the picture, and the reected light is passed through the objective lens 38, thence through the apertured mask 39, to the cell 33. The electric variations set up by the cell 33, and the 1800 cycle current in secondary 32 are impressed across the input electrodes of `a suitable grid-controlled vacuum tube or audion 40, with the result that there is produced in the output of said tube 40 a current of a fundamental frequency of 1800 cycles modulated in accordance with the shade values of successive elemental areas of the picture. It will be understood of course, that the drum 25 is advanced longitudinally, a predetermined amount for each revolution thereof. Preferably, although not necessarily, each revolution of drum 25 corresponds to 2400 impulses of current from generator 29. For a more detailed description of this portion of the system, reference may be had to Patent No. 1,593,651, granted to Austin G. Cooley. The modulated 1800 cycle impulses may be amplified further by a suitable vacuum tube amplifier 4I and then impressed upon the telephone line 42 by a coupling unit 43, it being understood that the Boston subscriber has meanwhile called the New York subscriber who has answered the call in the usual way of placing a telephone call. Unit 43 may be of any Well-known construction but is preferably of the type disclosed in said application Serial No. 103,506.

' At the New York subscribers station, there is provided a pick-up unit 44 which may be similar to unit 43. The output of unit 44 is amplified by a suitable vacuum tube amplifier 45, and is applied to the primary winding 46 of a transformer which is provided with three separate secondary windings 4l, 48, 49. Winding 4`I is connected to the input electrodes of a suitable vacuum tube .amplifier 50, the output of which is applied through coupling transformer 5I, to the recording lamp 52, a suitable apertured mask 53 be-` ing located between the lamp and the sensitized paper wrapped around the scanning drum 54. A suitable optical system represented schematically by lens 54a forms on the sensitized film an image of the illuminated aperture in mask 53. Drum 54 is driven preferably by a 90 cycle synchronous motor 55 which in turn is controlled by a 90 cycle generator 55, the latter being driven by an 1800 cycle synchronous motor 5'I which in turn is #controlled by the 1800 cycle current from winding 48 after amplification by tube 58. The

to motor through transformer 60. Motor 55 rotates drum 54 in synchronism with drum 25 `thus causing the transmitted picture to be reproduced on the sensitized lm wrapped around drum 54 in the well-known manner.

For the purpose of retransmitting the 1800 cycle picture currents to another subscriber, for example the Toronto subscriber (Fig 1), the current in secondary winding 49 after amplification in tube 6|, is applied to a coupling transformer having a primary winding 62 and two separate secondary windings 63, 64. The current in winding 63 after amplification in vacuum tube 65, is fed through coupling transformer 66 to the recording head 61 of a suitable electromagnetic recording device having a stylus which is oscillated in synchronism with the currents from transformer 66, as is well known in the phonographc and sound recording arts. Associated with the recording stylus 61 is a cylindrical drum. 68 on which is mounted a cylindrical wax blank, the drum with the blank being rotated at the desired speed by a motor 69 preferably,

`although not necessarily, of the synchronous type.

Also associated with drum 68 is a phonographic translator 1| which is preferably mounted to be moved longitudinally of the drum, so as to Start the phonographic reproduction at any desired part of the record as is well known in the phonograph and dictaphone arts. Device 1I translates the phonographic record into corresponding electric currents. 1t will be understood of course, that the heads 61 and 1I may be mounted in threaded engagement with a suitable lead screw so as to move the heads longitudinally in timed relation to the rotation of drum 68, it being understood that by suitable decoupling means, for example a split nut coupling with the lead screw,

,each head may be adjusted to any desired position longitudinally of the drum end. The phonographic currents generated by reproducer 1l are then applied to a coupling device 12 which may be similar to devices 43 and 44 and by means of which the 1800 cycle picture modulated currents are applied to the telephone line 13 leading to the Toronto subscriber. It will be understood that the New York subscriber has previously placed a call and has been connected in the usual way with the Toronto subscriber. From the foregoing, it will be seen that the phonographic record is being made by device 61 at the same time that the picture is photographically recorded on drum 59. Consequently, should any time elapse between the completion of the telephone connection to the Toronto subscriber and the beginning ofthe photographic recording, this may be taken care of by advancing reproducing head 1I so that the repeating of the phonographic currents to the Toronto subscriber does not take place until the latter has answered the telephone call and is in readiness to receive the currents. Consequently, no portion of the picture is lost by the Toronto subscriber.

, When the transmissionis tobe repeated over a carrier telephone channel, there may be introduced what is known as a frequency drift. There are disclosed in said Patent 2,138,398, certain methods of compensating for this frequency drift in order to use the fundamental frequency of the picture currents for syn- 4a suitable modulating arrangement.

No. 1,691,071. 4fore a modulator as well as an amplifier, the

chronizing. However, where Asuch 1 frequency' drift compensation is not desired, the synchronizing may be effected locally atthe New York subscribers station and at the receiving subscribers station. For example, assume that the pictures are to be yrepeated from New York to San Francisco. After the received picture currents have been recorded on the wax blank on drum (i8l as above describedthis blank may be transferred to another similar drum 14 which is driven-by an 1800 cycle synchronous motor 15, the drum being advanced longitudinally in the properv timed relationY similar to the advancement and rotation of the drum 25 at the transmitter. The motor 15 is controlled by a tuning fork 16 Which. is associated with a vacuum tube amplifier 11. The'amplied currents resulting from the interaction of the tuning fork and the amplifier tube are applied to motor 15. Preferably the motor 15 is geared to the drum 14 so that the latter makes one revolution for each 2400 impulses from the fork 16 in order that the reproduction by the reproducing head 18 may be at the same rate as the scanning at the Boston transmitter. The currents from reproducer 18 vare applied to the carrier telephone line 19 pref- .windings 82, 83. Winding 82 impresses the picture currents on the recording lamp 84 the light from which passes throughl a suitable apertured mask-85 and a lens system 85 toy form an elemental light spot on the sensitized film wrapped around the recording drum 81. Drum 81 is driven by a synchronous motor 88 which is contrclled by a tuning fork 89 and amplifier arrangement 90 is similar to the tuning fork 16 at the New York station. Consequently, the picf ture currents are received and reproduced at the same rate as they were originally transmitted from the Boston oflice. Should it be desired to retransmit the picture from San Francisco to Los Angeles over the non-carrier telephone line 9i, and without employing a local synchronizing source at the Los Angelesl subscribers station, the synchronism may be effected by the frequency of the picture currents themselves. For

this purpose, a portion of the` picture currents rreceived at the San Francisco station are applied through transformer winding 83 to a suitable vacuum tube detector 92 in the output circuit of which there are produced currents corresponding yto the shade values of the original picture. Associated with the tuning fork 89 is a pick-up coil 93 by means of which la current of 1800 cycles per second is impressed upon the coupling transformer 94. The currents in the secondary of the transformer 94 and the detected picture current from tube 92 are impressed upon Since ,the output of detector` 92 is in effect a variable amplitude D. C. signal the tube 95 and associated input circuit including resistance 96 and battery 91 are 4of the so-called direct coupled amplifier type as illustrated for example in U. S. Patent The tube 95 is in reality theremodulating signal ,beingderived from forkf89.

zamlrwy There is thus produced in the output of tube 95 an 1800 cycle current modulated in accordance with the original picture-signals', and this current may be coupled to the telephone line 9| bya coupling device 98 similar to devices 43, 44, 'IZFand 80. At the Los Angeles station, there is provided a photographic recorder 99 similar to recorders 54 and 8l, which is operated in synchronism with the transmitter drum by the 1800 cycle component of the received picture currents.

Fig. 3 shows a modification of the invention wherein all stations, from the originating station kto the various receiving stations, are synchronized by a frequency component of the picture currents.

`InKFig. 3, the picture is assumed to be transmitted from the San Francisco subscriber by means of picture transmitting apparatus such as described forY example in connection with the Boston transmitter (Fig. 2) the transmission being over a non-carrier channel to the Sacramento subscriber who is equipped with recording and .repeating mechanism such as disclosed in said application Serial No. 149,848. The pictures are recorded at the Sacramento station and are repeated by carrier telephone to the Omaha sub- Scriber Where they are repeated over the noncar-nier` line |0I to the Chicago subscriber. Assuming the'transmitter atthe San Francisco station produces a picture signal in the form of an 2,1800` cycle modulated wave, then therecording apparatus at Sacramento will be synchronized by the 1800 cycle component. However, .because of the carrier telephone link between Sacramentoand Omaha, the carrier demodulating equipment in the telephone plant may intro- .duce a frequency drift or distortion by the time the picture signals are received by the Chicago subscriber.V In order to maintain proper sync hronismby the synchronizing component of the picture, notwithstanding this frequency drift, a frequency drift compensator can be employedv at the Chicago station. One form of such compensator is disclosed in said Patent 2,138,398. Breferably, the drift compensator is locatedv at an intermediate point of the system, for example" at Chicago, the picture signals beingpreferably received from the telephone line |0|, by an 4inductive coupling device |02 as disclosed in said application Serial No. 103,506. being-acted on by the compensator |00, the picturecurrents are applied to the photographic reproducer |03 which is synchronized by the-1800 cycle component of the currents flowing from the ,cernpensator |00. These compensatedcurrents arealso repeated through respective repeaters |04, |05, |06, to the associated telephone lines leading'to rother subscribers as shown. Each of these other subscribers is provided ,with a photographic recording mechanism which is maintained-in synchronism by the 1800 cycle com` .ponent of the received picture currents.

` Preferably, the drift compensator |00 is of the type shown in Fig. 4l, wherein the conductors |01, |08, correspond to the same conductors of Fig. 3. For purposes kof explanation, let it be assumed that thelSOQcycle picture current repeated from Sacramento is changed by the carrier telephone Vequipment in the telephone plant at Omaha, so that there is repeated to Chicago a picture current of 179,9` cycles per second. In order to effect proper synchronism at Chicago and succeeding stations, it is necessary therefore, to convert this 19.9...yclecl0dulated picture current into a After similar 180.0 Vcycle current.. v5 `The.1'799 cycle Acurrent receivedover conductors |01 is applied to a modulator tube |09 of the audion type which is also fed'with current from a source of oscillations 0 of known fixed, but higher, frequency. For example, source ||0 may Agenerate asustained wave of 10,000cy'cles vper second.v The upper beat frequency between the 1799 cycles and tht-:10,000 vcycles is, then applied toa demodulator tubev Il'of the audion type which yisalso fedfrom'a source l |2of sustained Wavesbut of variable frequcnifso .that in the output circuit ofthe demodulator ||'|,th`ere` is produced an 180|), cycle wavefjbearingfthe originahpictiire` modulations. Thus 'under the above assumption,

the @sallam u2 is adjusted to beat witnthe `ing the compensator prior to actual reception of the picture signals, it is necessary that the oscillators l l0 .and ||2 be synchronized at the same frequen cy.V For this purpose, the oscillators may be connected to -the coordinate deflectin'g plates..

HB, -I l1 of a cathode-ray tube oscilloscopeof any well-known construction. `An attendant can by examining the patternV traced on the fluorescent screen of the oscilloscope, determine,r instantaneously whetherfthe sources H0 and I|2 are synchronoussynchroniaed and the picture signals are received overconductors |01, the r`attendant can determine by observing` thetarget H3 whether the oscillator I|2 shall be increased or decreased ,in

After .the oscillations have been frequency so as tomaintainian. y18.00 cyclecurrentfinH conductors |08. Q If the picture currents that are repeatedthrough the Omahastation to Chicago v are also' to be recorded locally at-the .Omaha Station. then @local frequency drift comscribers station so ,that the local recording ythereat caribe compensated for' frequency driftin the manner described in said Patent 2,138,398.

While specific apparatusy and f circuit arrange- ,45 pensatorlmayfbe: provided `at the l.Omalfla subments have been Yreferredjto herein, it will be understood that various changes -andmodifications may be made without departing `from the spirit and scope of the invention. f

1. In a telefacsimilerepeating system, a rst telephone subscribers 'station,.a second telephone subscribers station, a third telephone s ubscribers station, a non-carrier telephone line linking vthefirstand second stations, a carrier .11

telephone line linking the second and third stations lwhich line lis subject to frequency drift in the telephone plant, means at said first station including a facsimile scanner to generatev picture currents in the .form'of an audiofrequency carrier whosefrequency is locked vwith the/speed of the transmitting scanner, a picture reproducing means at said second station including motive means controlled by said carrier, means to repeat the picture currents from the second station to the-third station over said carrierline, the. last mentioned means including a tuning fork .controlled phonographic repeater at the second station, anda tuning fork controlled photographic. reQQrder theV Said third Station duceV the picture ,therefrom substantially free from the effects of frequency drift in said carrier channel.

r2. Af system according to .claim 1 in which a @fourth vtelephone subscribers station is connectedby a non-carrier line to said third station, said third station having means to detect the picture signal modulations in the picture currents received thereat and means to modulate a regular frequency current controlled by the tuning fork at said third Vstation by said detected currents, said modulated .currents being applied totheline leading to the fourth station, and a nel in series with a carrier channel which is subject to Vfrequency drift, means located bef tween the junction of said physical and .carrier channels to overcome the effects of said frequency drift, the last-mentioned means including a beat frequency modulator onv which the received picture currents from the carrier channel are impressed and a beat frequency demodulator connected to the output of said modulator, and a facsimile reproducing mechanism at said distant station having its vscanning mechanism synchronized with the transmitting scanner under control of the output of said demodulator.

4. In a facsimile system of thetype wherein the facsimile signals are generated in the form of a modulated audio frequency current whose frequency is locked with the speed of the transmitting scanner, which signals are to be transmitted to a distant station over a physical channel in series with a carrier channel which is subject to frequency drift, means to repeat the signals from the carrier channel to the physical channel so as to be free from the effects of frequency drift while maintaining synchronism with the transmitting scanner, the last-mentioned means including a pair of oscillators, means to beat the picture currents received from the carrier channel with one oscillator to Yproduce a beat frequency, means to lbeat the said beat frequency with another oscillator to produce another beat frequency, and means to apply said other beat frequency to said physical channel to control the facsimile reproducing light source of a receiver'connected thereto andv to synchronize the facsimile scanning mechanism thereat with said transmitting scanner.

5. In a facsimile system of the type wherein the facsimile signals are generated in the form .of a modulated audio frequency carrier whose frequency is locked with the speed of the transmitting scanner which signals are to be trans- 6. In a facsimile systemof the type wherein lthe-facsimile signalsV are generated in the form to' receive the repeated currents and to repro-` of a modulated audio frequency current whose frequency is locked with the speed of the transmitting scanner which signals are to be transmitted to a distant station over a physical channel in series with a carrier channel which is subject to frequency drift, frequency drift compensating means between said channels including a pair of normally synchronized oscillators, a beat frequency modulator for producing a beat bef tweenthe first oscillator and the signal currents, abeat frequency demodulator'having its output 'controlled by the output of said modulator and the second oscillator, one of said oscillators being adjustable as to frequency in order to maintain a predetermined fixed frequency in the signals applied to said physical channel, a facsimile reproducing mechanism at the receiving end ,of said physical channel and having a scanner mechanism synchronized with the transmitting scanner by said fixed frequency,. and means as-fv the facsimile signals are transmitted over a physicalchannel in series with a carrier channel which is subject to frequency drift, means including a transmitting scanner to transmit facsimileA signals in the form of an audiofre-r quency current over said carrier channel to a repeater station while maintaining the facsimile transmitting andv receiving scanners at the ends of saidcarrier channel synchronized by local os'-,A cillators, and means to retransmit said signals over said physical -channel to a distant station, the last-mentioned means including a detector for detecting the signal modulations as received from said carrier channel, means to derive an audio frequency carrier from the oscillator local to said repeater and for modulating said derived audio frequency carrier by said detected modulations, a facsimile reproducer at said distant station having means to synchronize it with the .transmitting scanner under control of the said frequency of said derived carrier whereby the facsimile reproduction at said distant station is substantially free from the effects of frequency drift in said carrier channel. f

8. In a system for transmitting facsimiles between a first station and a second station which are linked by a physical telephone channel in series with a carrier channel which is subject to frequency drift in the telephone plant, means at said first station to transmit facsimile signals in the form of a modulated audio frequency carrier, an intermediate station located between the physical and carrier channels, means at said intermediate station to record and to retransmit said signals under control of the record, the speed of said recording means being locked with the transmitting mechanism at the first station 'by the intermediary of said audio frequency carrier, a third station connected to said intermediate station by said carrier channel, means at said third station to retransmit said signals to said second station in the form of a modulated audio frequency carrier substantially free from the effects of frequency drift in said carrier channel, the last-mentioned means including a local source of oscillations at said third station, means v at said third station to detect the picture signals received over said carrier channel, meansat saidy third station to modulate said local oscillations by said detected signals, means to transmitsaid modulated oscillations to said second station. and a facsimile reproducer at said second -station which is synchronized with the transmitter at the rst station by the frequency of said received oscillations.

9. The method of transmitting facsimiles over a carrier telephone channel which is subject to frequency drift in the telephone plant, which method includes the steps of transmitting the facsimiles in the form of a modulated carrier Wave, receiving the modulated Wave and detecting the signals therefrom, generating local oscillations at the receiving station Whose frequency is independent of the frequency drift introduced in said carrier channel, modulating said local oscillations by said detected signals, retransmitting said modulated local oscillations to a third station in the form of an audio frequency lcarrier Whose frequency is locked with the transmitting scanner, recording the picture at said third station under` control of the received signals and controlling the synchronism of the recorder at said third station by said received carrier frequency.

AUSTIN G. COOLEY.

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