US1892371A - Method of picture transmission - Google Patents

Description

METHOD OF PICTURE TRANSMISSION Filed Oct. 8. 1930 menu: 12 RECORD kmngnsiz mm:

Q INVENTOR FRANZ TUCZE K ATTORNEY T0 RE C OIDER Patented Dec. 2 7, 1932 UNITEDTSTATES' FRANZ TUCZEK, or BERLIN, enn-irraux nssrenon T SIEMENS & HALSKE, 'AKTIENGE jSELLSCHAFT, or SIEMENSSTADT, NEAR BERLIN, GERMANY, aoonronnrron 0E GERMANY Application filed October 8, 1930, Scrial No.

ping the light at the sending end, say, by the aidof a revolving perforated disk, current impulses reach the line whenever the scanning pencil of light happens to impinge upon.

abright spot on the picture. Now, if'the receiver is so designed that blackening of the incoming or re-created picture occurs when current comes in, while no blackening happens in the absence of current, then, as will be'seen, a negative'picture is re-created.

This case, for example, will arise when the modulated oscillations come to act upon a Kerr'cell or else when the recording is accomplished by electromagnetic means and ways.

In order to obtain a positive picture, va-- rious methods/have been disclosed in the prior'art. For instance, it has been suggested to utilize a second photoelectric cell upon which comes'to actchopped-up light, but no light modulated by the picture to be t-ransmitted. By taking care so that the currents of the two photoelectric cells, i. e., the picture cell and the compensator cell,will come to co-- act in asuitable manner, for instance, by pro.- viding a bridge arrangement, not only can the picture be reversed or transposed, but

such an arrangement is further adapted to regulate the degree of modulation both in sending positive as well as n'egative'pictures. This is not only desirable :in frequent in stances, but even imperative," if theincoming stancyin the properties of the cell.

and re-created pictures areto be made perfeet,

But'this method involves 'several shorts comings. 1 In the first placethe'use of two cells instead of merely one cell is expensive and notconvenient in practical operation owing to-the limited life and the absence of con- The circuit elements at the input end of an amplifier possessinghigh amplification, which are re quired on changing from positive to negative transmissions, are apt to c'onduce to difliculties, such 1 as increased capacitance, tendency to oscillategreception and picking up of stray currents. 'Furthermore, with the method stated, reversalisfeasible only in the trans? PATIENT. OFFICE.

I 7 METHOD OEPICTURE TRANSMISSION 487,117, and in Germany September 6,1929.

mitter, while it may also be desirable to effect such reversal in the receiver apparatus.

For instance, if a plurality of transmitters correct amplitude the carrier currents modu latedb'ythe picture currents with currents of 7 like frequency generated by a small a. c. dy-

namo or' the like, such as a tone-wheel or sirene. Thephase can be so adjusted in this scheme that the currents'corresponding to white surfaces or spots are wholly or partly compensated for positive pictures or else so that their amplitudes are augmented by cooperation with'the acoustic wheel for negative pictures. What is presupposed is that the added currents and the carrier currents have constantly and permanently the same frequency, an aim which is attained in the 1 -perforated-disk method by drivingthe per-' forated disk and the tone-wheel by one and the same motor, most preferably. by seating them upon thesame spindle. If the currents are combined in the receiver, then the tonewheel mustbe driven from a motor running in synchronism with the sending-outfit motor, for, example, the motor driving the cylinder-of the incoming picture. Adjustmentof the correct phase relations maybe'efi'ected by turning the stator of the tone-wheel, or else by shifting theoptical' means parallel to'the circumference of the perforated disk. An-

other chance to adjust conditions consists in displacing the rotor of theftone-wheel or else .the perforated disk spective spindle.

The arrangement can be made'particularly simple-if the perforated or serrated disk is made of iron, and if the teeth which periodically mask the lightare' at the same time used for 'the generation of the alternating current magnetic flux. This form of construction offers this advantage that, upon exchanging the perforated disksye. g., for changing over to another carrier frequency, not only the freangularly upon the requency of the compensating current will automatically be made equal to the carrier frequency, but that also the phase relations are preserved. It is also easily possible in this scheme to make the wave shapes of the two cooperating currents identical in that the cross-sectional shape of the magnetic flux is adapted to the cross-section of the pencil of light rays.

Regulation of the desired amplitude conditions can be accomplished by regulation of the filament current, by the use of variable resistances or attenuating means, or by regulation of the exciting current used for the tonewheel. It may be recommendable in this connection in addition to adj ustability of the amplitudes of both currents, to provide a certain interrelationship, say, betweenthe exciting current and the tube (lamp) current in such a manner that, when the picture currents become smaller owing to decrease of the lamp current, also the current of the tone wheel becomes simultaneously smaller so that the degree of modulation or compensation is preserved.

Since, generally speaking, the curve-shape of both currents will be different, it is recommendable to insert in the long distance line or in the wires brought to the radio transmitter, an electric filter for smoothing, for instance, a coil low-pass filter.

The combination of the two currents may be efiected at different places. The tonewheel should be as small as feasible in order to save expense. Hence, if a relatively large output power is required, for instance, in radio or air-line operation, such combination most suitably is to be effected between two tubes of the amplifier, while in the case of low output powers such as needed in telegraph work, it is most suitably effected at the output end of the transmitting amplifier. If the tone-wheel is mounted at the receiving end, the currents most conveniently are combined at the input end of the amplifier.

The accompanying drawing illustrates several modifications of the device above described wherein:

Fig. 1 illustrates one form of alternator; Fig. 2 illustrates a modification; and Fig. 3 illustrates a system for producing the reversing action at the receiver in combination with the arrangement shown by either Fig. 1 or Fig. 2.

The construction of the alternator may be chosen the same as that of any ordinary alternating current machine. In order to save cost it will be found desirable to have recourse to the well-known sirene type of alternator (Fig. 1) in which the rotor 1 has no winding, while the stator 2 consists of a sim-' ple magnetic yoke comprising two poles 3 and 4.

Another embodiment is shown in Fig. 2. In this case the perforated disk 5, preferably according to Fig. 1. The teeth mask the light periodically, thereby effecting the optical analyzing.

By Fig. 3 a complete system is shown wherein at the transmission point a synchronous motor or the like 8 is driven from an a. c. line and arranged to rotate the chopping disk 9 which is placed immediately in front of the photo tube 10. The picture record 11 is illuminated from a light source 12 and the light signals brought to act upon the photo cell 10 are periodically interrupted by means of the rotary disk 9. The amplitude modulated signals, modulated in accordance with the tonal density of the picture record,

are amplified and transmitted by the am li; a

fier and transmitter 11 and then receive the receiving point by the receivlng and amplifying device 12 from which they are transferred to a recorder system, not shown. Sinnlarly to the point of transmission, the receiver recording device is driven by means of a synchronous motor 13 which can, if desired, be connected to the same a. 0. supply line. As the motor 13 is rotated, it drives a generator 1, for example, of the type shown by Fig. 1, and by suitable arrangement of the pick-up device generally designated as 14, the amplitude and phase of the locally generated signals may be determined, The phase is determined by shifting the pick-up device to the right or left as shown, and the amplitude may be controlled b moving the pick-up device radially inwar or outward from the tone generator.

Having now described my lnvention, what I claim and desire to secure by Letters Patent is the following: I

1. The method of producing picture reversal and regulating the modulation in picture telegraph apparatus which comprises generating carrier currents and modulating said currents by currents representing the varying intensities of light and shadow of the picture elements of the transmitted record, simultaneously generating at the receiving point other currents of the same frequency as the carrier current generated, and adding the two generated currentsin predetermined phase relationship so as to produce either positive or negative picture reproduction at the receiving point.

2. The method of producing picture reversal in picture telegraph apparatus which comprises generating a carrier frequency, modulating the carrier frequency by signal ios impulses correspondin tothe varying in- 1 tensities of light and s adow of the picture elements, generating at a receiving point a, second frequency corresponding to that of 5 the carrier frequency, and regulating both I currentsin size and in phase so as to selectively create at the receiving point positive or negative pictures and control the picture modulation, 7 i 10 r In testimony whereof Iafiix my si ature, FRANZ TU ZEK.

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