US1937754A

US1937754A - Telephony

Info

Publication number: US1937754A
Application number: US407974A
Authority: US
Inventors: Marion W Gieskieng
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1929-11-18
Filing date: 1929-11-18
Publication date: 1933-12-05
Anticipated expiration: 1950-12-05

Description

TELEPHONY Filed Nov. 18, 1929- 2 Sheets-Sheet 1 7 5g 3 mm 52% H H $2 mm M mm Dec. 5, 1933. M. w. GIESKIENG TELEPHONY 2 Sfieets-Sheet 2 Filed Nov. 18, 1929 M f i I M M w 2 J W I lw M b I: w

Patented Dec. 5, 1933 TELEPHONY.

poration of limerica, notation Application November 13, 1929 Serial No. 407,974. r

Claims.

This invention relates to an. improved method and apparatus for transmitting sound and has reference more particularly to means for reducing static and other line interferences in con-v 5 nection with reproducing apparatus employing a vibrating beam of light and a photo-electric cell.

In that classof apparatus to which my invention relates, means is provided whereby. vibrations are imparted to a beam of ordinary light. or to a beam of cathode rays, which correspond to the vibrations of the sound waves, which it is desired to transmit. The beam is directed towards a photo-electric cell from which it is separated by a shield having an aperture or slot through which the light must pass before it can enter the photo-electric cell. The cell is COB-.- nected to the grid circuit of a vacuumptube amplifier in the plate circuit of which a telephone orother receiver is connected. v

When sound waves are transmitted to a distance by wires or by wireless apparatus and then reproduced as audible sound by means of a telephone or loud speaker apparatus, it is found that static'and other line interferences effect the reproduction adversely. and at times the static disturbances are'so great that they make the speech or other signal waves unintelligible.

The efilciency of a radio transmitter can be greatly increased without losing overtones, by the trimming of modulation peaks and my apparatus is especially adapted for this purpose.

By use of my apparatus it is possible to protect radio reception devicesfrom surges, modulation peaks and above all from atmospheric static to such an extent that the loudest crash of static will .be no louder than the loudest signal received, and it therefore makes it possible to receive weak signals and to limit the static to approximately the same level as the weak sig- 4 nals.

Theabove desirable results are attained by the simple expedient of forming the opening or window in the shield that is interposed between the source of light and the photo-electric cell in a way that willbe hereinafter described and to employ in combination with such a shield a narrow beam of light that is wider than the widest portion of the window.

It is well understood that the amount of current that will-pass through a photo-electric cell tric cells of photo-electric wave transmitting circuits theshield is provided with. a slot or open- 4 ing which lies in the path of a beam of light that is reflected from a mirror that is vibrated in ac: cordance with the sound vibrations that are to be transmitted; this beam. is partially intercept- 6(t ed by the shield or screen and that portion of'the' beam that overlaps the window enters the photo-- electric cell causing a varying area of the cathode surface within the-cell to be illuminated with the result that slight changes are produced in currents flowing through the 'cell whichcorrespond strictly to the vibrations of the light beam, and these variations are then amplified'by well known means.

It is evident that with an apparatus like that shown and described in'U. S. Letters Patent No.

1,527,649, the variations in"the current that passes through the photo-electriccell 'will'always be directly proportional to the amplitude of the" vibrationsfof' the light beam and thereforeatmospheric static will cause loud crashing sounds that drown out the other signals with the result that thesou'nd produced by the receiving apparatus will vary greatly from that which is being transmitted.

I have found thatif the light beam employed is narrow in the direction in. which it vibrates and Wider than the window in the screen and if the window is of such shape that the width of the opening. therein is different at different points along is length, greatly improved reception can be obtained.

By this simple expedient it is also a beam of cathode rays is vibrated by an electromagnet;

Fig. 3 is a view showing the relationship ofth light, the-mirror, the photo-electro cell and? the screen;

opening;

Fig. 4 is a view of a screen showing one form of Fig. 5 isa diagram'showing the relationship "of the curves of the opening in the screen at-the transmitting circuit :end and the receiving end of. the

Fig. 6 is a view similar to Fig. 4 and shows a modified form of opening;

Fig. 7 shows a screen having an opening designed for secret transmission; and

Fig. 8 shows another form of opening.

In the drawings the transmitter 10 is provided with a diaphragm 11 which is vibrated by the action of the sound waves. A mirror 12 is mounted for oscillation about a pivot 13 and is connected with the diaphragm 'by means of a thin rod 14 which transmits motion from the diaphragm to the mirror. A'lamp 15 is located a short distance from the mirror and is preferably separated from the latter by a screen 16 that has a narrow slot through which the light may pass to the mirror. Located in the path of the reflected beam is a screen or shield 17, which is provided with a window, or opening 18 that has a peculiar shape and through which the light must pass in order to enter the photo-electric cell 19. The photo-electric cell is of the usual construction and comprises a sealed tube having a central anode 20 and a cathode 2 1, which consists of a coating of silver which has been formed on the wall of the tube and upon which has been deposited metallic potassium. Before finally sealing, the tube is subjected to a Geisler discharge in an atmosphere of hydrogen. An opening 22 is left in the cathode to provide a window for the passage of light which falls upon the interior surface of the cathode.

When this cellis placed in series with a suitable source of potential, the current therethrough is dependent upon the quantity of light entering the cell or the'area of cathode illuminated. The exact form of photoelectric. cell is immaterial and any form can be used. The term photoelectric cell or .photo electric device is intended to apply to any means which has the property of changing the current passing therethrough in response to any change in the quantity or area of illumination to which the cell is'subjected, regardless of the rate at which the changes in illumination occur.

In operation, the beam of light 23, oscillates in accordance with the vibrations that are imparted to the mirror 12, either by the diaphragm 11 or by the armature 24 of the galvanorneter25. The transmitter 10 is used at the transmitting end of the line and the galvanometer 25 at the receiving end of the line. The amount of light that en-. ters the photo-electric cell depends on the posi-.

tion of the beam of light with respect to the opening 18 as this is so constructed that its width variesin a manner that will hereafter be described. It is apparent from Fig. 3 that if thebeam moves in the direction of arrow a, it will move from a narrow to a wider part of the opening and therefore the amount of light that enters the photoelectric cell will increase, whereas, when it moves in the opposite direction, the amount will decrease. The rate of increase and of decrease will be controlled jointly by the rate of vibration of the beam and the rate at which the width of the beam opening increases or decreases at the particular point where the beam is located.

The variation in the illumination of the photoelectric cell will cause variations inthe current the resistance, preferably through a few battery cells 31 to maintain the proper difference of potential between the filament and the grid The plate circuitis supplied from a battery 32 and included in the plate circuit are the

transmission lines

33 and 34 across which are connected the receivers or the loud speaking reproducing devices 36 shown in Fig. l.

With the parts assembled as shown in Fig. 1, let us assume that a sound is produced at S adjacent to the transmitter 10. This will cause the diaphragm 11- to vibrate and this in turn will vibrate the mirror 12 about its pivot 13 and this will cause the beam 23 to vibrate and to move back and forth over the screen 17 and the window 18 whereupon the illumination in the cell will be varied and this will set up a variable current through the photo-electric cell which will be amplified and flow through the primary coil of transformer 37 and thereby setting up a corresponding current in

lines

33 and 34. A galvanometer 25 is connected with line 34 through a potentiometer 3'7 and therefore the mirror 12a, will be vibrated and cause the beam of light to move'over the opening in screen 17 whereupon a current will be set up in the loud speaker circuit 36 and this will operate the loud speaker or the headset 39. There is a difference between the openings 18 in the screen at the transmitter and at the receiver and this has been illustrated in Figs. 4 and 6 in which the full line represents the outline of the opening in the former and the dotted line the shape of the opening in the latter while OB represents a line with respect to which the full line and the dotted line curves are symmetrical or nearly so. In order to explain the theory of theoperation, reference will be had to Fig. 5 in which the straight line OB corresponds to the lines so indicated in Figs. 4 and 6 and which will be considered as being the upper edge of the opening through which light passes. If the ordinate OY represents the amount of light that is admitted to the photoelectric 'cell' at the transmitting end and the abscissa OX'the'quantity of light that is admit- 1.

ted'to the photo-electric device at the receiving 'end wewill that if line OB makes a 45 degree angle with the abscissa that the input and output will be the same and therefore 0c equals ob. The static and other line disturbances are not generated in the transmission device but are picked up on the line between the sending and the receiving stations and are sometimes of greater intensity than the signal currents. If the openings in the two screens had straight relatively inclined sides, the static and other foreign currents would produce sounds that had the same relation to the signal sounds as the relative values of the currents'and the static disturbances and line noises would'therefore drown out the signals. 3-1

-over the air in magnified form and when they reach the reproducing apparatus tc reduce them 1 to the same extent as the magnification whereby they will produce the same effect as if they had been transmitted by an ordinary apparatus. -The static and other line disturbances which come onto the line between the two stations are not amplified, but are subjected to'the same reducing effect as the signal currents whereby the static and other undesirable currents are greatly reducedwhile the signalcurrents are first amplified'and then reduced. Since the intensity of 1' the sounds reproduced depend on the amount of light that enters the photo-electric cell at the receiving station-and since this is determined by the width of the opening 18, it is evident that beam of light is projected onto the screen 17 at the sending station and that an amount equal to five units would enter the cell when the beam. was in the position indicated by line 'be if the edge of the opening were along a straight inclined line OB. Since the opening is curved as indicated by the solid line 12 units of light will enter the cell instead of 5 and this will be equiv al'ent, in effect, to light of the value of 0d entering the opening at f if the edge'of the opening were straight as indicated by line OB, the effect on the action of the photo-electric cell will therefore be the same as if the beam had been swung to g h. In order to reduce the eifect at the receiving station, the opening has its corresponding' side reversely curved as indicated by the dotted line and the beam of light will strike the curve 'of the opening at the receiving end at h which permits 5 units of light to enter; Let us now suppose that static to a value equivalent tofive units of light is picked up by the circuit. Since this is not amplified'it will be effective to move the light beam to eb which will produce an effect equivalent to a single unit (02'). From the example given, it will be seen that the signal will be reproduced at its original value, but static and line disturbances will be greatly diminished by properly shaping the openings in the screens 17. I a

In Fig; 4., line 01B has been inclined thirty degrees, instead, forty-five, as in Fig. 5, but the operation is the same. In Fig. 6 both sides of the opening are curved but the variation per unit of length is the same as in Fig. 4 and thereforethe eifect is the same.

If secret signals are to be sent, the screen at the sending station may be provided with several indentations along its edge or edges like those shown in full lines in Fig. 7, and the screen at the receiving station having reversed indentations somewhat as shown by dotted lines. These screens are provided in sets which are properly coordinated and when used as described, the one at the sending endwill effectively scramble the signal and the one at the receiving end unscramble the same so that it will be intelligible.

11 Fig. 2 I have shown an apparatus in which a beam of cathode rays is employed in the place of the light beam. Cathode rays can be influenced by an electromagnet and therefore instead of using a galvanometer an electromagnet 40 is arranged adjacent the beam and subjected to a variable current produced by a telephone transmitter or which may be obtained from the lines 33 and 3c. The beam 41 will be vibrated over a shield 17 that is formed from material opaque to the cathode rays and which has an opening 18 like that already described. 7

Instead of a loud speaker or a telephone receiver a suitable automatic recorder may be used when the device is employed for telegraphy.

By using a screen like that shown in Fig. 8, a

multiplication of the frequency can be obtained. It is desirable to so adjust'the partsthat the light beam will vibrate equally on opposite sides of the line OY because atthis point the maximum magnification of the signal currents is obtained as Well as the maximum reduction of-the static disturbance and therefore within a range that can be designated the noiseband the objectionable currents will be quite effectively eliminated. .l l

If we consider that those portions of the opening that have been designated by- X in Fig. l are the ones employed for signals of the usual intensity, then thoseportions of the curved sides beyond this area can be of; smaller inclination with respect to the direction of travel of the light beam and therefore'the variations in the illumination of the photo-electric cell will be compara tively small for the light beamtravel beyond this portion of the curve. i

Where radio frequencies are used, the cathode .ray beam is preferablyas when this is employed there are no moving parts that have inertia and therefore the beam can be vibrated at any irequency within the capacity of the electromagnet, and the photo-electric device.

The limiting properties of the window 18may be so designed that static or other interferences or cross talk can be held within any desired levels when used with telegraphy, telephony,'.facsimi1e, 1'. 5 television, etc. Thisdevice when properly connected and adjusted will hold all peaks or surges within the operating limits of the. transmitter due to the absolute limiting and. smoothingfeature of window 18. This device or limiter can be used in series to alter to a liner degree the response to certain energylevels. Frequency multiplication can readily be obtained by properly designing'the window. 2

It is also possible to obtain somewhat similar results .by magnetic means but since this is a different invention, itwill not be described herein.

It is evident that it is the relative movement between the window and thebeam that produces the result desired and it is therefore possible to move the screen 17 instead of the light beam, but such reversal is obviously useful only where slow variations are suilicient for the purpose under consideration. Since cathode rays can be used as well as light rays the term light beam should be construed as covering both.

Although the screen 17 has been described as provided with an opening 18, it is evident that it may be made of glass or other material that is transparent to the rays used and have portions 13; covered with an opaque substance or any other equivalent means may be substituted. A suitable metal screen is believed to be the most desirable but glass may be used and even metal when used with cathode rays. 5

Having described the claimed as new is:

1. A method of reducing interference in transmission systems Which consists in vibrating a beam of light in accordance with sound waves, 14g projecting said vibrating beam upon a light sensitive element to transform said vibrations into current variations, controlling the projec tion to produce distorted current variations, amplifying the distorted current variations, transmitting the amplified variations through an interference region, collecting transmitted distorted variations and interference currents, and treating the combined distorted variations and interference currents so that the distorted va- 150 invention what is riations are de-d'istorted to conform with the original sound waves and. the interference is limited to substantially the same level as the weak components of the sound waves.

2. A method of reducing interference in transmission :systems which consists in vibrating a beam of light in accordance with sound waves projecting said vibrating beam upon a light sensitive element to transform said vibrations into current variations, controlling the projection to produce distorted current variations, amplifying the distorted current variations, transmitting the amplified variations through an interference region, collecting transmitted distorted variations and interference currents, and converting the I combined distorted variations and interference currents to light vibrations, and transforming the latter to current variations in a manner such thatthe distorted variations are. de-distorted to conform with the original sound waves and the interference is limited to substantially the same level as the weak components of the sound waves.

3. A method of reducing interference in transmission systems which consists in vibrating a beam of light in accordance Withsound Waves projecting said vibrating beam upon a light sensitive element to transform said vibrations into current variations, controlling the projection to produce distorted current variations, amplifying the distorted current variations, transmitting the amplified variations through an interference region, collecting transmitted distorted variations and interference currents, and converting the combined distorted variations and interference currents to light vibrations, and transforming the latter to current variations in a manner in verse to the original distortion step so that the distorted variations are de-distorted to conform with the original sound waves and the interference is limited to substantially the same level as the weak components of the sound Waves.

4. A communication system comprising a transmission station including means for conthrough said medium, means for converting the combinedvariations and interference currentsto light vibrations, means for transforming the latter into current variations, and means for controlling the transformation so that the distorted variations are de-distorted to conform with the original sound Waves and the interference limited to at least the same level as the weak components of the sound waves. a 5. A communication system comprising transmission station including means for converting sound Waves into light vibrations, means to convert light vibrations into current variations, means to amplify the latter, and means for controlling the light vibration conversion in a predetermined manner so that current variations are produced distorted with respectto the sound waves, a transmission medium responsive to interference currents, a receiving station including means" for collecting distorted current variations and interference currents transmitted through said medium, means for converting the combined variations and interference currents to light vibrations, means for transforming the latter into currentvariations, and means for effooting the transformation in a manner inverse to transmitter istortion so that the distorted variations are de-distorted to conform with the original sound Waves and the interference limited to at least the same level as the Weak components of the sound waves.

MARION W. GIESKIENG.

lilo