US2336932A - Facsimile retransmission method and apparatus - Google Patents

Description

AMP

MOD.

Dec. 14, 1943. a G. FRAIM 2,336,932

FACSIMILE RETRANSMISSION METHOD AND APPARATUS Filed April 3 1941 AMP Z INVENTORS viii/.433?

Patented Dec. 14, 1943 FACSIMILE RETRANSMISSION METHOD AND APPARATUS Everett G. Fraim, Hicksvllle, N. Y., assignor to Press Wireless, Inc., Chicago, 111., a corporation of Delaware Application April 3, 1941, Serial No. 386,646

Claims.

This invention relates to facsimile systems and more particularly to systems of phonographically recording or retransmitting facsimile signals.

It has been proposed heretofore to record phonographically at a distant receiving station received facsimile signals, and to use the phonographic record to control the retransmission to another point or points. An exampl of such a system is that disclosed in U. S. Patent No. 1,669,222 to C. A. Clarke. I have discovered that these prior proposals are not entirely satisfactory particularl where the signal are t ansmitted over a radio link or over a wire line which is subject to channel interruption or fading. Furthermore, with these prior systems, I have found that the inconstancies in speed of the motor driving the phonographic recorder and the photographic reproducer may b suflicient to mar the retransmitted copy and in some cases to render it useless for ordinary commercial purposes. In accordance with this invention, it is possible to record and retransmit picture signals, facsimile signals and electro-optical signals generally, without introducing distortions such as those mentioned above. This result is accomplished by transmitting the picture signals in the form of a modulated alternating current carrier and recording the received signals phonographically in such a way that the speed of the phonograph turn-table or th like i not electrically locked to the speed of the transmitting facsimile scanner. The speed of the phonographic recorder can then be chosen to suit the particular conditions to be found during retransmission.

The invention however is not limited to the retransmission of the signals from the receiving station to a distant point. Thus in certain cases, it may be desirable to record a picture phonographically at a receiving station rather than to reproduce the picture directly as a facsimile from the received signals. In other cases it may be desirable to have a phonographic record at the transmitter so as to monitor or play-back the picture or facsimile signals after transmission. In still other cases it may be desirable to record phonographically a transmission at a speed of recording which is different from that at which the local facsimile recorder normally runs. Subsequently, this abnormal-speed" record may be is shown in the drawing in schexwtic form, a typical facsimil system embodying the features of the invention. Inasmuch as picture transmitting systems and apparatus are quite well-known, and since the invention is concerned primarily with the non-facsimile recording portion of such a system, only so much of the facsimile apparatus is disclosed as is necessary to a clear understanding of the invention. However, as an example the invention may be used in connection with a picture transmitting system of the type shown in application Serial No. 301,563. Furthermore, while the term "phonographic" is used herein as applied to a recorder or reproducer, that term is used in its wider sense to include not only wax disc or cylinder recordings, but also photographic recordings such as are employed in sound recording and reproducing systems. In fact, any known method of sound recording and reproducing may be employed in connection with the present invention.

Referring to the drawing, the numeral I represents any well-known form oi facsimile scanner including for example a rotatabl drum 2 around which the picture 3 or other subject matter is wrapped. Associated with the scanning drum is any well-known form of pick-up l by which the picture 3 is analyzed in successive elemental areas and the shades thereof translated into corresponding electric signals usually by mean of a photo-electric cell or the like. In order that the entire picture can be so scanned, the drum 2 may be advanced along its axis a predetermined distance for each complete revolution thereof thus causing the picture to be scanned in successive adjacent parallel lines.

For the purpose of rotating the drum, 9. driving motor 5 may be employed and energized from the supply source 6 of constant frequency. It will be understood that the source 5 may b of any well-known type of standard frequency, for example a tuning-fork-controlled oscillator whose output is sufficiently amplified to drive the motor 5, or this standard frequency source can be used to control a speed adjusting arrangement which in turn controls the speed of motor 5. In this latter case the motor 5 may be driven from the A. C. mains. Suitable reduction gears I may be provided between motor 5 and the driving shaft 8 of drum 2. The picture current signals from device 4 are applied to an amplifier-modulator 9 of any well-known type which i also fed with a carrier wave from source l0. Preferably, source i0 supplies an audio frequency carrier, for example of 1800 C. P. S. The output of device 9 is then a modulated audio frequency carrier wherein the modulations represent the picture current signals from device 4. It will be understood of course that the signals from device 4 may be used to amplitude-modulat the carrier from source III, or they may be used to frequencymodulate the waves from source ID in any wellknown manner. The modulated carrier is then passed through a suitable amplifier ll prior to being impressed upon the signalling channel l2 which may be a wire or radio channel.

At the receiving station. the modulated audio frequency carrier is amplified in a suitable amplifier l3 and the modulations representing the shades of the picture 3 are demodulated in any well-known form of demodulator l4 whereby they are converted into corresponding D. C. signals. The demodulated signals are applied to an amplifier-modulator device l5 which is also fed with constant frequency alternating current from source I6. Source l6 may be a standard frequency source such as a tuning-fork-controlled oscillator or the like. The driving motor I! can be supplied with power from the local commercial power means for example 60 cycle mains. The motor I! drives through suitable gearing iii, the phonograph turn-table IS on which the record blank 20 is carried. The modulated carrier output from device I5 is applied to the phonographic recording unit 2| the stylus 22 of which engraves the blank 20 with a single frequency wave, that is, the frequency of source l6 and with cutting amplitudes corresponding to the original picture signals.

When it is desired to retransmit or "play-back the facsimile signal on record 20, it is transferred to a phonograph reproducer comprising the turntable 23, driving motor 24 and gearing 25. Motor 24 may be driven from the same A, C. supply mains as that which supplies motor l'l. It will be observed that the turn-table l9 and motor I! used for recording may also be used for reproducing. The record 20 in the form of a single frequency cutting having amplitude variations representing the facsimile signals is translated by any suitable pick-up comprising for example stylus 2B andtranslater unit 21 by which the cutting is translated into a corresponding modulated carrier wave. The frequency of the wave from device 21 will then be the same or a fixed multiple of the frequency of source l6 plus or minus any variation introduced by inconstancies in speed of turn-tables l 9 and 23. The modulated carrier wave from device 21 after suitable amplification in amplifier 28 is applied to the reproducing light source 29 or to the corresponding reproducing element of any well-known form of facsimile reproducing machine. The facsimile reproducing machine may be of any well-known type and merely for purposes of illustration it is shown as of the type employing a rotatable drum 30 around which the recording film or paper 3| is wrapped. Drum 30 is arranged to be rotated about its axis and advanced longitudinally thereof so that the recording film or paper 3i is exposed in successive elemental areas in successive parallel lines. The drum shaft 32 is driven through suitable gearing 33 from a motor 34 which is controlled or. operated by the carrier frequency from unit 21. Preferably, an amplitude limiter and leveler 35 of any well-known type is connected between unit 21 and motor 34 so as to maintain a substantially uniform level in the waves of the current applied to the motor winding. It will be understood that the carrier wave plied with an 1800 C. P. S. signal.

from device 21 instead of operating motor 34 directly, may control a tuning fork or other wellknown frequency responsive element which in turn controls and maintains the motor 34 in synchronismwith the said carrier frequency. With this arrangement therefore, the actual facsimile recording on the surface 3! is independentof any minor inconstanciesgeither in the speeds of the motors H or 24 or in the speeds of the turn-tables l9 or 23. Consequently, if the sources 6 and it are accurately controlled as to frequency, the record which is produced on the recording surface 3| will be substantially independent of any variations of speed in the phonographic recording and reproducing mechanisms. .As an example of the flexibility which is provided for repeating and reproducing, assume that drum 2 at the transmitter runs normally at a lower speed than the recording drum 30. Thus drum 2 may run at 50 R. P. M. and drum 30 may run at R. P. M. It will be assumed further, that drum 30 rotates at 100 R. P. M. when motor 34 is sup- Turn-table I9 is then set to rotate at 30 R. P. M. by motor I! and the standard frequency source l6 will supply a standard frequency carrier of 900 C. P. S. to the modulator l5, whereby the received facsimile sig nal is recorded on blank 20 as a 900 C. P. S. wave with amplitude modulations representing the shade values of the original picture 3. Since the motor 34 is designed to run under control of an 1800 C. P. S. signal, the motor 24 which drives the reproducing turn-table 23 is set to drive said turn-table at 60 R. P. M. thus causing the original recorded 900 C. P. S. carrier wave to be converted to an 1800 C. P. S. wave which controls the motor 34. It will be clear of course, that this is merely one example wherein the phonograph recording speed on blank 20 is one-half the phonograph reproducing speed. This ratio of speeds may be varied to suit conditions which may arise either during recording point or during retransmission. Thus, the phonograph recording on blank 20 if desired, may be at a higher speed than the phonoraph reproducing speed providing of course the relative speeds of the motors l1 and 24 are such that the proper carrier frequency signal is supplied to motor 34.

What I claim is:

1. In a facsimile system, means to receive facsimile signals in the form of a modulated carrier, means to demodulate said carrier, a phonographic recorder machine including a driving motor driven from local power mains, a source of standard frequency which is local to the recorder means to modulate current derived from said standard frequency source by said demodulated facsimile signals, and means to apply said modulated current to the recording element of said phonographic recorder to produce a record in the form of a modulated single-frequency carrier.

2. In a facsimile system, means to receive facsimile signals, a locally synchronized facsimile recorder for said signals, a driving motor for said facsimile recorder, a phonographic recorder including a motor driven from the local power mains, a source of standard frequency local to the recorder, means to modulate current from said standard source bythe received facsimile signals, means to energize the recording element of said phonographic recorder by said modulated current to produce a phonographic record thereof, a phonographic reproducer for translating said phonographic record back into a corresponding modulated alternating current, means to control the recording element of the facsimile recorder by the last-mentioned modulated alternating current, and means to control the driving motor of the facsimile recorder by said last-mentioned modulated alternating current.

3. A facsimile system according to claim 2 in which the last-mentioned means includes a wave limiting device for converting the modulated alternating current to one of substantially uniform amplitude prior to applying it to said motor.

4. In a facsimile play-back system, means to receive facsimile signals in the form of a modulated carrier, means to demodulate said carrier, 9. local source of audio frequency carrier, means to modulate said local source by said demodulations, means controlled by said modulated local carrier to produce a phonographic record in the form of a modulated single frequency audio frequency carrier with the modulations representing transmitted facsimile signals, a phonographic reproducer, a facsimile receiving machine ineluding a facsimile reproducing unit and a driving motor, means to control the facsimile reproducing unit by the single frequency carrier currents from the phonographic reproducer and means to control said motor also by the single frequency carrier currents from said phonographic reproducer.

5. In a facsimile transmission system, means to receive facsimile signals in the form of a singlefrequency modulated carrier, means to detect said modulations, means to. convert said modulations locally into a modulated carrier frequency F1, means to repeat said recorded signals phonographically at a different carrier frequency F2, a facsimile recorder and a motor for driving said recorder, means to control said motor controlled by said frequency F2 whereby a facsimile of a transmitted picture can be reproduced regardless of variations in speed of the phonograph record- 0 ing or phonograph reproducing mechanisms.

EVERETT G. FRAIM.

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