US2380667A - Signal modulation means - Google Patents

Description

y 1945. M. MRR|soN 2,380,667

SIGN AL MODULATION MEANSv v Filed Aug. 4, 1943 s Sheets-sheet 1 July 31, 1945. M. MORRISON 2,330,667

SIGNAL MODULATION-IMEANS I I Filed Aug. 4,1943 :5 Sheets-Sheet 2 i ABCDEF INVENTOR Mfl/VTFORD MORE/SON Jul '31, 1945.

Filed Au 4, 1943 a: F\./r--. G

I. X \l amma aw as 'INVENTOR MON7FORDMORR/50N Pmmed July 3.1, 1945 UNITED STATES PATENT oFF cs r SIGNAL Max:121 MEANS Montford Morrison, Upper Montclair, N. J. Application August 4, 1943, serial No. 497,347 .5 Claims. (Cl. 178-17) This invention relates to systems of telegraphic transmission in which optical pick-up of the signals is used, and relates in particular to such systems employing carrier currents.

Among the objects of the invention are; to provide a simple and eflicient means for generating a large number of accurately-fixed carrier frequencies; to provide a simple and efl'ective means for modulating the light, used in the optical pickup system, into sinusoidally varying beams before the beams are employed in the pick-up operation; to provide means for the simultaneous application of a plurality of scanning beams to a single signal copy to be transmitted; to provide means for use of both the transmitted and the reflected light from the signal copy, in the optical pick-up system; to provide means for the transmission of Baudot-and other similar codes to receiving stations not equipped with synchronized apparatus; to provide means for transmission of Baudot and other codes under conditions which greatly reduce the errors of'reception, due to interference; to provide a method of telegraph transmission directly from a plain letter text without requiring synchronism at the receiving station; and

to provide a modification for letters, numerals and other signal characters used in telegraph transmission, which reduces the band-width of the transmission frequencies required and reduces the interchannel interference in the receiving circult-filters.

Further and other objects will be obvious from the specifications when read in connection with the accompanying drawings; and the scope of the invention is set forth in the claims hereto.

In the drawings:

Fig. 1 is a partial section of one embodiment of the invention used as a transmitter; Pig. 2 is an enlargement of a section ofFig. 1, taken at the plane marked A-B in that fi ure and looking west, Figs. 3, 4, and 5 are enlargements of different modifications of the circular tracks shown in Pig. 2; Fig. Gisasectionoflfig. 1 takenatthe plane 0-D of that figure and looking east, and with a tape-puller added for cleamess; Fla. 7 is an enlargement of a fragmentary view of Pig. 6 taken at the plane E-F and looking east, and which shows the channel form of guide for the transmission tape; S. 8 is a rear view of that part of the tape channel shown in Pig. 8, between the dotted lines 6-H and I-J; Hg. 9 is an en-' largement of the tape shown in Fig. 6: and Fig. 10 is a form of transmission tape used for Baudot.

andothersimilarcodes.

In Fig. 1, Us a constant speed motor which may be of any form whatever, and its function is to revolve the shaft 2 at a highly constant speed. This may be a small synchronous motor directly applied to a constant frequency alternating current system; it may be a synchronous motor driven alternating current derived by amplification from a tuning fork oscillator; or, preferably, it may be of the highly. constant speed form driven directly from a direct current source, as described in my co-pending patent application filed July 28, 1943, Serial Number 496,389.

Onto shaft 2 is mounted a plate 3, which may be constructed in a variety of forms. The construction of plate 3 will be better understood from Fig. 2 which is a fragmentary enlargement thereof. Plate 3 may be constructed of a photographic film or, preferably, a photographic plate, in which latter case, there-is a freedom from shrinkage.

Plate 3 is provided with a series of light tracks,

The light tracks produced on plate I are formed into continuous circular paths.

These light tracks, or carrier-current frequency tracks, revolve continuously behind a slit I I, Figs. 1 and 2, which slit is sufficiently narrow to provide substantially sinusoidal variation in the total light flux that is permitted to be transmitted by means of the combined action of the revolving carrier frequency track and the stationary slit, as will be appreciated by those skilled in the art to which this invention appertains. In some cases, instead of a photographic plate, I may use a thin metal relatively opaque plate provided with perforations, such as shown in Fig. 3, and which provides the same character of light fiux modulation, but the pattern of the perforation is mod.-

ified so as to permit more metal to be retained.

between perforations, thereby retaining considerable strength in the metal plate.

Returning to Fig. 1, i2 is a so-called exciter .lamp, of a conventional variety, such as used in standard 35 mm. motion picture optical sound systems; i! represents a conventional set of conderising lenses which focuses the light onto the revolving carrier frequency light tracks. in a manner somewhat similar to the way in which the light is focused on sound track in a motion picture film; the diiference being that in a motion lens system ll, which accurately focuses each beam onto a desired part of the tape it, which is shown in its edgewise position in the figure.

An enlarged section of tape it is shown in Fig. 9, which comprises a translucent paper support i8, onto which specially-designed characters l1, fl and I! are printed. These characters are preferably printed on both sides of the translucent support IB. This double printing increases the opacity of the characters and thereby improves the quality of the optical pick-up.

The rectangles 10 to 28 represent the images of the combined slit and carrier frequency tracks, as projected upon the tape is, Fig. 1.

These images 20 to 28, inclusive, vary in in-' tensity sinusoidally with the period equal to that of the carrier frequency of a telegraph channel which these frequencies represent in the output circuit, as will be hereinafter more fully described. That is, each rectangle varies in light intensity in such a way, if the light represented by this image were fed directly to a photoelectric cell, unmodulated carrier current would be developed in the photocell circuit. As the tape I! with the characters H, II and i9, is pulled into the field of these light beams, modulation is produced by the absorption of light by the opaque characters, as will be understood by those skilled in the art.

Returning to Fig. 1, the seven light beams fall upon the tape is which is moving in th'vertical direction to the plane of the paper, and as the white translucent paper passes through the light beams, some light is transmitted directly through the paper, as indicated by lines 21 and photocell 2!, which forms a part of the amplifier circuit 2!, having an output 38.

Si is a concave reflecting surface, and the tape II is so located with reference to the focus of the surface 81 that a considerable amount of the light reflected back along such lines as 12, and is-aiso directed to the photocell 28 along lines such as 33.

By such a structure the photocell 28 receives light by direct transmission through the paper tape ii and also, by reflection, from "the surface of the paper, providing a high emciency in the optical system.

- As tape ll moves across the paths of the various light beams, modulations in accordance with the character of relatively opaque configurations on the tape are produced in the currents of the photocell 20.

Referring to Fig. 0, which is Fig. 1 taken atthe provided with a gentlespring actuated member 8!, Figs. 6 and 8.

Referring to Fig. 8, this is a fragmentary view of the part of the channel 34 which lies between the dotted lines 6-H and I-,J, and the member I6, Figs. 6 and 8, is a loose channelled part held by a fin spring 31, which is fixed to pins 38 and 89 on a channel part and to a loose member 36 by pin 40. 43 is an opening in the channel. 34 to permit the transmission of light at this location.

The function of this member 36 is to keep the tap I! pressed against the lower side of the channel ll, keeping the characters accurately located with reference to the modulated light beams.

Referring to Fig. 9, I prefer to modify the configurations of the letters and characters in such a way as to reduce the rate-of-change inthe light modulation produced by the character. As the character moves into the light image, instead of striking a parallel line, I prefer to use a graduated area such as shown in 4| which reduces the rate-of-change, as will be understood by those mathematically equipped in the art of optical light pick-ups.

Fig. 10 shows the embodiment of my invention as characterized by a tape operated in the place of the tape shown in Fig. 9, used for the purpose of transmitting Baudot code signals and signals by other similar codes. In this case, instead of transmitting a complete character in a single channel, I may employ five simultaneous channels represented by the light images 20, 21, 22, 24

and 25 providing the live units required for the code. The light imag 26 provides an orientation frequency which goes out with the code signals and may be recorded simultaneously at receiving stations, and later the messag decoded without the use of synchronism during recepplane 0-D and looking east, this shows the loca- .tion of the characters facing the optical system Fig. 7 is a fragmentary view of Fig. 6 taken at the dotted line E-F and looking east, and shows the channel 34, Figs. 6 and 7, through which the tape is pu led, and in Fig. 6, atape puller is indicated for clearness.

The characters ABCDEF, etc., are accurately located on tape II with reference to the lower side ll of the tap ii. The channel N, Fig. 6, is

tion.

- In Fig. 10, to the left of the dotted line K-L.

dots may be supplied with boundary lines functioning as modulation modifier, as will be understood by those skilled in the art. and as illustrated in the figure.

The use of five simultaneous channels for the transmission of Baudot code, reduces the interference effect upon the signals, since all of the interference is applied to all the signals of one character at the same time. Where only one unit is sent at a time, the interference effect is differ-- cut for different units of a single character, which is conducive to errors.

The terms print" and paper" are used in this specification in a perfectly general sense, and are not to be construed narrowly.

What I claim is:

l. The method of optical scanning of printed the modulation rate-of-change at the boundaries of said configurations under scanning operation by said field, and causing optical scanning bymoving the said series of characters in a. direction orthogonal to one side of said field.

2.-The method of optical scanning of printed signal characters which comprises creating a rectangular field of continuous sinusoidally varying light-flux, creating a series of printed signal characters having configurations presenting boundary lines to said field under scanning to reduce the modulation rate-of-change at the boundaries thereof and causing said field to optically scan said characters. I

3. The method of reducing threshold rate-of: change in signal modulation systems employing optical pick-up, comprising creating a scanning light-flux field adapted to movement in a direction relatively identical with the precessional direction of signal characters on a printed copy, said field having an outline normally conducive to the production of high threshold rate-oi-chanse under optical scanning of signal characters formed by lines orthogonal to said direction,

creating signal-character configurations on said copy adapted-to reduce said .rate-of-changaand .tape having light transmitting characteristics and a plane surface having light reflecting characteristics; areas of said tape having light transmitting and light reflecting characteristics diiierentfrom those of the main body of the tape; the boundaries of said areas along lines transverse of said tape being substantially serrate in form. L

5. A tape for use in facsimile transmission; said tape having light transmitting characteristics and a. plane surface havinglight reflecting characteristics; areas of said tape having IighttranSmit-J ting and light reflecting characteristics difierent from those of the. main body of the tape;'said areas having a plurality of extensions .along'the the boundaries thereof transverse of, said tape; said extensions extending longitudinally of said tape and diminishing in transverse Width as they extend away from said areas.

' MONTFORD MORRISON.

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