US1642637A - System of facsimile telegraphy by wireless signals - Google Patents

Description

Sept. 13:, 1927.

1,642,637 E. BELIN SYSTEM FACSIMILE TELEG RAPHY BY WIRELESS SIGNALS Filed Sept. 5, 1924 TZ'LEE.

Mung/w T Recorder fl'ecel var Q Loco) 0307/07?- Patented Sept. 13, 1927.

UNETEQ STATES PATENT QFFEQE.

EDOUABD BELIN, OF PARIS, FRANCE.

Application filed September 3, 1924, Serial No. 735,605, and in France September 27, 1923.

The invention relates to the transmission of pictures and more particularly to the radio transmission of pictures which are composed in whole or in part of infinite 8 gradations of light and shade between max1- I mum and minimum illumination. In a copending application Serial Number 8,022, filed February 9, 1925, it has been pointed out that such a method of transmission is 10 applicable to both line drawings, manuscripts, and the like which may be described as having high contrast and photographs, lithographs and the like, which have relatively. low contrasts between adjacent porlii tions.-

The condition of any given portion of a photographic picture is a direct index of the degree of illumination of the corresponding portion of the object photographed, and may 3i? be expressed mathematically as a function thereof and varying proportionately thereto: that is, the picture may vary either in relative translucency at the point in question,

or in relative thickness if a gelatine coating be employed. This relative illumination may therefore be expressed by a current which varies in amplitude proportionately therewith. If successive points of the pic ture be explored by a translating apparatus 30 to so express the variations of illumination,

the current resulting will be of a character similar to a telephone current, but non-oscillatory, being at times constant for an appreciable period and at times varying from 85 minimum to maximum in periods anywhere fromseveral seconds to a very small fraction of a second, and may according to the present invention be used to modulate by action either upon the potential of a direct current, or the amplitude, or the frequency or both of a carrier current.

In the system of facsimile telegraphy, described in my U. S. Patent No. 915,154, transmission is effected by the slight difierences in level of the surface of a relief photograph or the like. These differences in level, by their action upon a variable resistance, vary the intensity of a weak current passing through the resistance proportionally to such difierencesinlevel, and therefore, ac-

cording to the differences of light and shade of the photograph or the like to be transmitted. This weak varying current must be suitably amplified before it acts upon the wireless transmitting apparatus proper. The amplifier employed for this purpose is of the resistance type and has no condensers or transformers through Which-the varying continuous current in the circuit must pass so that due to the absence of resistances the amplified currents or electrical variations faithfully follow the differences in level of the surface explored.

It is likewise possible with the present invention to employ a translucent positive or negative picture having relative gradations of light and shade, and to produce therefrom a varying current which faithfully follows in amplitude the lights and shades of the picture. and then at the receiving end to obtain from this current a photographic positive or negative.

This invention comprises a transmitting station at which is located means for gener-' ating a direct or a carrier wave current, and apparatus adapted to impose upon such current modulations which are a function of the relative light or shade of the picture it is desired to transmit; and a receiving station at which is an apparatus adapted to receive the modulated current from the transmitting station, and to produce a beam whoseluminosity varies as a function of the modulations of such current, which serves to transliate these modulations into photographic efects. v The transmitting and receiving apparatus are synchronized with respect to each other by Ways and means well known in the art. Since such means form no part of the present invention, they are not shown nor described in detail.

The preferred form of this apparatus has been found in practice to give excellent re- .sults where the communication between the two stations was established through the natural media; but obviously the system is likewise applicable to work along intervening metallic or other conductors as well.

The accompanying drawings set forth diagrammatically means of accomplishing the invention, and

Fig. 1 shows a transmitting circuit for radio communication With modulation amplifiers and a modulating and oscillating tube.

Figure 2 is a diagram indicating" the apparatus employed at the receiving station.

Fi re 3 shows a modified transmitting circuit in which the microphone is supplie with an alternating current.

In Fig. '1 the variable resistance M, which in construction may be a carbon pile such as a microphonic transmitter button, is acted upon in accordance with the varying level of the surface ex lored, in the manner shown in my U. S. atent No. 915,154. As the speed of the record is not so high as to set up free oscillations of the mova le parts of the microphone by shock excitation in any substantial degree its resistance chan es in exact correspondence with such irregu ar or non-oscillatory variations; and correspondingl affects the current flowing from the loca source 2, through it and the regulating resistor 1. This current is applied to the gri and filament of an amplifying tube A; and by its potential creates corresponding and amplified variations in the potential across the plate circuit resistance 5, from the plate battery 4. These variations are-in turn amplified by the second tube B and succeeding tubes if any, with resistance couplin indicated at 8 and biasing battery at 6. a will be understood that any suitable number of these tubes may be employed, until the resultant current is sufiicient to serve for mod ulation. In practice, such an amplifier of three or four properly regulated stages is sufficient to modulate a transmitting system of several hundred watts when the resistance of the variable resistora microphone button-only varied a few ohms (equivalent to three or four watts at most) under the pressures; this represents veryt feeble variations of the grid potential for t e first tube.

Such an amplifier may be used if the micro hone is fed with continuous current. It is likewise possible to employ an alternating current whose amplitude varies with the pressures exerted on the aforesaid variableresistance, and such alternating current may be amplified by the ordinary amplifier with transformers or resistance coupling as usually employed in a wireless telephonic transmitting station. However, where the modulating current is a direct current which may remain constant for appreciable periods of time the modulation of the carrier wave by such irregular variation of the direct current cannot e likened to that which obtains in wireless telephony, as an oscillatory wave or a wave of musical frequency is not superposed for modulating the high frequency oscillation. It is proposed rather to translate irregular differences in level in the surface explored into corresponding irregular variations of the amplitude or of the frequency or of both amplitudeand frequency of the high frequency oscillations. A striking difference between the modulating current produced from the ordinary telephonic transmitter and that produced by this system is due to the tendency of the diaphragms ofsuch transmitters to make independent oscillations; whereas in the present case, the amount of movement in either direction is not oscillatory or of true wave form but a precise function of the irregular variations in the picture, and is in no wise independent thereof. 7 a

Figure 1 shows one very suitable example of a circuit arrangement which is a type of the absorption system well known in wireless tele hony.

Ti. cult of the last amplifying stage is connected between the filament and the grid of a group e resistance 8 placed in the plate cir-i of tubes one of which is shown at C, termed absorption tubes, whosefilament plate re sistance constitutes a variable non-reactive lmpedance. Biasing batteries 9 are placed in the grid circuits of the tubes so as to obtain suitable modulation which is thus made as proportional as is possible. The filament plate circuit of tube C includes the inductance coil 14. The oscillating or control valve D is connected to deliver into this latter V circuit high frequency oscillations by means of the grid inductance 10 in electromagnetic relation to the portion of coil 14 utilized as a plate inductance, with grid leak 12 and condenser 11, plate condenser 15, and plate battery 13. Since the internal resistance of the absorption tubes varies with the current from the microphone, the resistance of the output circuit of these tubes must vary with the relative illumination of the original obect.

Furthermore, since the impedance of the high frequency circuits varies, in which the absorption occurs, a change of wave len th results whose effect is peculiarly favora le for reception, as will be described hereafter.

Whereas wireless telephone reception ma take place without a heterodyne (the higli frequency wave serving only as a carrier for the audible frequency oscillation which reproduces the voice) for receiving signals transmitted by the present method a heterodyne is used to establish a beat fre uency with the received high frequency oscil ation. It has already been stated that the oscillations change amplitude each time that the pressure upon the variable resistance changes. These changes of amplitude are to be reproduced at the receiving station as modulations on a relatively very low frequency, thus necessitating the use of a heterodyne. On the other hand, the wave length of the transmitting station also changes (very feebly it is true) With the modulation, so that the low frequency produced by the beats of the heterodyne itself varies both in amplitude and in frequency. The wave received at the indicating apparatus passes from 1500 cycles to. 400 or 500 cycles, for example, when there is pressure on the variable resistance.

3 In the system set forth in the aforementioned patents, reception of pictures to produce a range of light and shade takes place by the aid of an oscillograph, traversed by the emergent beam from a lamp and shutter device responsive to the transmitted current, and it will be easily understood that an oscillograph, by reason of its low yet appreciable inertia, is very sensitive to the variations in frequency of the received current, much more so than to the variations in intensity of the current.

At high frequencies, say above 1500 cycles, the movement will be very small for a given intensity of reception. For lower frequencies, however, this movement may become considerable. Therefore in the range below approximately 1500 cycles may be found all the degrees of freedom required for use in this apparatus.

It will be understood that it is possible, for receiving, to add together the two effects,

- viz changes of intensity and changes of frequency; moreover, that the record produced by the luminous spot of the oscillograph can be controlled by changing the frequency of the heterodyne. This latter may be effected by using instruments whose own period is variable or by employing receivers which are more or less tuned. It will also be under stood that positives or negatives may be produced by adjusting the frequency of the heterodyne below or above that of the oscillator at the transmitting station.

It is possible to feed the transmitting microphonic circuit at the transmitter with alternating current of audible frequency, which ma then be amplified by means of the ampli ers ordinarily used in telephonic transmitting stations. In this case, referring to Figure 2, there is useda small oscillator E of musical frequency (for example, 600 cycles), having the grid inductance21, plate inductance 20, plate battery 22, and regulating plate condenser 23. By means of a variable contact on its plate inductance, this oscillator feeds a photographic variable resistor M of the same type as that described above, with an oscillating or alternating current, according to its internal resistance. The local circuit of the resistor is then arranged across the grid and filament of the first amplifying tube A or in the primary of a transformer 24 which acts upon such tube A as shown in the diagram. The amplifier is similar to those employed in wireless telephony stations, while the modulation process may be any suitable process. Reception takes place without a local heterodyne, and

the low frequency oscillation of 600 cycles is directly modulated by the resistor having an ordinary receiver with or without reactance.

It has also been stated that oscillograph instruments are above all sensitive to changes in frequency; by the last arrangement described, variations of amplitude of the low frequency oscillations received are alone obtained. The frequency of the low frequency oscillator of the transmitter may also be acted upon in the same manner as described for the transmitting station in the first arrangement.

It is apparent that this invention is not restricted to the particular circuits and ar= rangements shown and described, and I do not desire to'limit myself'except within the scope of the appended claims.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1; The method of transmitting gradual, irregular, non-oscillatory electrical variations representing gradual variations in light and shade between successive points on a picture by radio frequency carrier waves and receiving the same with an oscillograph receiver responsive to variations in frequency of a relatively low frequency carrier current, which comprises transforming the electrical variations into corresponding variations in frequency of a radio frequency carrier current, transmitting the radio frequency carrier current to a receiving station and at the receiving station heterodyning said radio frequency carrier waves to produce a variable frequency carrier current of the said relatively low frequency to which. the osciilograph is responsive and varying in frequency in accordance with the variations in frequency of the radio frequency carrier wave.

2. The method of receiving frequency modulations of a carrier wave and recording the same in direct or inverse magnitude at will, which comprises, a combining with the received modulated waves heterodyning waves of a frequency above or below the limits of variation of frequency of the received waves to cause the beat frequency produced thereby to vary directly or inversely,

according to the kind of record desired, and

produce beat oscillations varying in freqpency, in accordance the variations in equency of the received oscillatlons, and

It'd

an oscillograph recorder at the receiving station differentially responsive to the differcnt frequencies of the variable frequency heat waves.

4. In a system for modulating high freuenc currents with gradual non-oscillatory e ectrical variations comprising, an audion

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