US1914898A - Method of transmitting telegrams and pictures on short waves - Google Patents

Description

June 20, 1933. F. SCHRCYTER ET AL METHOD OF TRANSMITTING "IELEKGRAMS AND PICTURES ON SHORT WAVES 1950 2 Sheets-Sheet 1 Filed Oct. 11,

ATTOfiNEV l INVENTORS FIUTZ 5CHR6TEZ BY WILHELM RUNGE June 20, F scHRdjTER ET AL METHOD OF TRANSMITTING TELEGRAMS AND PICTURES ON SHORT WAVES Filed 6st. 11, 1930 2 Sheets-Sheet 2 a Ahem Patented June 20, 1933 UNETED STATES tenses PATENT GFHQE FRITZ SGHBUTER AND VIILHELIVE RUNGE, OF BERLIN, GERMANY, ASSIGNOBS TO TELE- FUNKEN GESELLSCHAFT DBJAHTLOSE TELEGRAPHIE M. 13. 1'1, OF BERLIN, GERMANY, A CORPORATION OE GEBMQANY METHOD OF TRA'NSMITTENC- TELEGRAMS AND PICTURES ON SHORT WAVE$ Application filed October 11, 1980, Serial No. 487,973, and in Germany July 6, 1929.

The present invention is concerned with short wave transmission of telegrams or pictures with print, script or the like. In the use of short waves it has heretofore not been feasible to exceed a certain limiting value in the speed of transmission for the reason that, owing to certain'anomalous conditions in the propagation of short waves, telegraphlc and picture signals and impulses of a very short duration are recorded in appreciably spread form with the result that very high speeds of transmission is impossible, while in the particular case of picture transmission, small lettering or script, detailsof representation, etc., become illegible in that they merge or run together.

For instance, if as shown in the drawings, Figure 1, line 1, the transmitter is sending black-white signals in the form of amplitude values A of the high frequency wave in a time-sequence as shown by the shaded areas, these amplitudes reappear (as shown in line 2) at the receiving end markedly extended or enlarged as a consequence of the spreading efiect, so that a recorder apparatus mounted in the receiver and havlng a response threshold value A0, as will be noted, will register markedly enlarged black marks.

A principal object of this invention is to preclude the said harmful. effect (dash and space in atelegram and black-white constrasts of the picture being regarded as equivalent) \Vithout intending to thereby limit the scope of the invention, the latter shall hereinafter be discussed in connection with picture transmission work and in connection with the accompanying drawings, wherein Figure 1 is given by way or explanation of the present invention,

Figure 2 illustrates a transmitter incorporating the features of the present invention,

Figure 3 illustrates a receiver according to this invention, and,

Figure l illustrates in detail one of the amplifiers used in the apparatus shown in Figure 3.

The first assumption which is to be made is that the white spaces between black portions or signs, as is mostly true in the case of letters, script or print, are of greater length than the possible spread arising for such scanning speed or rate as may be chosen. Later on this limitation may be dispensed With. 5

The essential features of the invention are as follows:

Experience has shown that in the presence of the spreading effect peculiar to short wave transmission as hereinbefore described, the 6 beginnings of the constituent or elementary impulses (save an occasional Doppler effect) come in at the receiving end at the sametime intervals as the action of the copy of picture upon the photoelectric cell or the radiations 6 at the transmitter. This condition is clearly shown in line 2 of Figure 1 of the drawings, for the rises in amplitude at the receiving end present the identical time differences or intervals as the beginnings of blackened por- .7 tions in the original copy at the sending end shown in line 2.

Properly interpreting this situation, the beginnings of both the black and the white portions may be transmitted by two wave 7 trains of different frequency and that thus the change from black to white, and vice versa, could be brought about and'recorded at the receiver end by the instants of arrival of one frequency or of the other, as the a case may be, in accordance with the original copy, independently of the possible persistence of the frequency that preceded. v

This is the gist of the disclosure, it being presupposed in this connection that the two 3 frequencies present no greater difference than what is necessary with a view to obtain a convenient scanning speed and the corresponding band width of the modulation. It is necessary to keep this in mind in order that, say, owing to Doppler effect, the two waves may not exhibit unduly great differences in propagation times owing to undue deviation of the paths of the two waves.

The basic idea of this invention may be carried into practice in various ways, either by certain ways and means to be adopted at the transmitting end or at the receiving end. At the sending end, for instance, apart from the wave A1 which is radiated off during the 100 entire period of black picture portions, a detuned wave A2 is sent out immediately upon changing to white, said wave, however, to die down after a short while. Conditions are suitably so chosen that, including possibly arising spread effects with the white or space impulses on wave A2, the time of action of wave A2 at the receiving end will be smaller than the time required to cover the smallest white gaps, though always so great as corresponds to the spread of the black signals in terms of time.

The detuned wave A2 may then be used for the purpose of transiently raising the threshold value (of response) A0 to higher values A0 (as shown in line 4 of Figure 1 of the drawings) by means of producing a biasing potential by said wave A2 in the in put amplifier disposed below the recorder device or in the recorder means itself. In this manner the amplitudes or impulses adapted to reproduce the black portions of the copy and subject to the spreading effect at the receiving end will be accurately cut off at those points which correspond to the change from black to white in the original copy.

At the points of change from white to black, on the contrary, the blocking action of wave A2 has died out at the receiver, and the picture recorder or re-creater will then be 7 subject to normal control by wave A1. It will also be noted that the application of this method is also based upon that the beginnings of the wave trains A1 and A2 at the receiving end are with sufficiently great exactness displaced in time or spaced apart by an amount corresponding to and governed by the blackened portions of the picture or original copy.

Another mode of practicing the invention consists in that one operates at the transmitter with normal detuned waves, in other words, that one wave is sent out throughout the duration of white and of black. At the receiving end, the wave A2 starting upon the change of black to white precludes the continuation of recording of black for a length of time corresponding to the possible spreading of the impulses.

A means suited therefor consists, for instance, of a receiving element responding to wave A2 and which utilizes the potential built up by a certain number of high frequency periods for self blocking in known manner, it being feasible in'this scheme to give or impress upon the process the correct time constant, say, by capacity action. Until the instant when self blocking happens, the element responsive to wave A2 results in a control action which counteracts or prevents the flow of the inking or recorder current released by wave A1. The arrangement furthermore operates in such a way that self blocking, after wave A2 has ceased to flow, is rapidly eliminated, or better still, that this action is produced by the starting of wave A1, with the result that circuit conditions are again so that the spreading effect of the black signals or impulses is suppressed.

The use of keying and detuning waves for fixing the beginnings of black and white portions at the receiver end most suitably is so, however, that a circuit device or gear acting like a tumbler relay is caused to assume one position by the beginnings of wave trains A1 at which the inking current is allowed to flow, while it is caused to shift to the second position as soon as wave train A2 sets in where no recording currentshould flow. The arrangement thus operates independently of the changing times of persistence of one wave or the other. Of course, it would also be possible to design such a circuit scheme in a way so that it is free from inertia, say, by means of controlled thermionic tubes or by means of the ignition and extinction intervals of potential of the glow discharge (gaseous conduction) tubes, in order to attain high speeds of transmission.

As regards the transmitter it is further feasible to radiate energy only during very brief periods at the beginning of the black or the white picture portions in the form of two different wave lengths, in other words, to operate with short impulses, which, by virtue of the time difference in their beginnings in the receiver cause the change from black to white or vice versa with perfect faithfulness according to the original copy, so that, owing to the difference in wave length the sense or direction of such change is rendered absolutely clear. By the use of such short impulses it is also possible to overcome fading phenomena.

It will be understood that the sense of keying as shown in the drawings could also be reversed, in otherwords, wave A1 could be coordinated to white picture portions, and wave A2 to the black portions.

The possible transmission speed as already disclosed may be still further increased if the beginning of the first signal is determined and caused by an impulse having frequency f the end of the first signal by frequency f the beginning of the second signal by frequency 7}, the end of the second signal by frequency f while for the third signal again frequencies f and f are employed, and so forth. It will be noted that inside the time to be considered for the reverberation, two signals can be transmitted instead of only one.

By choosing a still greater number of frequencies, the speed of transmission can be correspondingly raised.

According to the invention as described in detail hereinafter more than two frequencies are used whereby impulses are transmitted Y to in order to identify or fix the beginning and end of the signals to be transmitted. In order to eliminate the harmful effect of the spreading of the signals upon the speed of transmission, a frequency is used for each impulse which differs from the preceding one. After reception of an impulse the receiver becomes insensitive to the frequency of this impulse for the duration of length of time that a possibly arising echo may have, so that the echo of an impulse, if present, is immaterial for practical operation.

This end may be attained, for instance, by the adoption of the arrangement shown in Figure 2. It is assumed in this instance that transmission is to take place on four frequencies, though it will be understood that the method here disclosed is applicable also to any other even number of frequencies. In this scheme the beginning of the first signal is to be fixed or identified by frequency 7}, the end of the first signal by frequency f the beginning of the next signal by frequency 2, and the end thereof by frequency f The assumption is made that the signals to be transmitted are in the form of D. C. signals or impulses impressed upon the primary terminals of transformer 5, whence they are imparted to the grids of two tubes 6 and 7 which are biased as far as the lower knee by means of the source of potential 8. The polarity of transformer 5 may then be chosen in such a way that, at the beginning of a signal a shock of potential will arise in the secondary of the transformer whereby the tube 6 is rendered conductive for a brief length of time, while the tube 7 continues to be blocked. At the end of a signal, tube 7 will then carry current for a short while, whereas tube 6 continues being blocked. For the transmission of the frequencies f f f and f the four transmitters S S S S are provided. S and S are connected with the plate circuit of tube 6, and S and S, with the plate circuit of tube 7 by way of key means relays well known in the art so that the transmitter remains in circuit as long as the corresponding tube 6 or 7, respectively, is conducting.

The transmitter S works upon the grid circuit of a'tube 11, the plate circuit of which includes three transformers 12, 13 and 14. The grid circuit thereof contains a condenser 15, which, by way of a tube 16 connected in parallel thereto may be charged up in this sense that the tube 11 is blocked and capable of being discharged through tube 17. The grid circuit of tube 16 is fed from the secondary of the transformer 12. The secondary of transformer 14, optionally by way of amplifier V is brought to the aerial. An entirely similar arrangement is provided in the rear of the transmitter S comprising tube 21, transformer 22, 23, 24, in the plate circuit of said tube 21, condenser 25 in the grid circuit of tube 21, tubes 26 and 27 which are adapted to charge up and discharge the condenser 25. The corresponding transformers etc., disposed in the rear of transmitters S and S respectively, are denoted by 31, 32, 33, etc., and 41, 42, 43, etc.

The secondary of transformer 13 feeds the grid of tube 27. The secondary oftransformer 23 feeds the grid of tube 37, transformer 43 feeds the grid of tube 17 The operation of this arrangement is as follows: Suppose the condensers 25, 35, and 45 are charged in such a way that the tubes 21, 31, and 41 are blocked. Hence, at thifinstant the transmitter S is able to work upon the antenna only by way of the unblocked tube 11 and amplifier V At the beginning of a signal, tube 6 is transiently rendered conductive, and the transmitters S and S, are cut in circuit for a brief time. The blocked tube 31 does not pass the impulse leaving the transmitter S but the non-locked tube 11 feeds the impulse of the transmitter S by way of transformer 14 to the antenna.

By way of transformer 12 it furnishes at the same time an A. C. potential to the grid of tube 16 which is thereby rendered conductive and which charges the condenser 15 in such a way that tube 11 becomes blocked. This blocking action does not occur instantaneously, but is retarded by a certain time constant which depends upon the capacity of the condenser 15 and the internal resistance of tube 16. At the same time, by way of transformer 13, the tube 27 is temporarily rendered conductive, and the condenser 25 is discharged. After the impulse S has been sent out the condensers 15, 35, and 45 are so charged up that the tubes 11, 31, 41 are blocked. that the tube 21 is rendered permeable.

At the end of the D. C. signal passing through the transformer 5, the tube 7 is temporarily rendered conducting, and as a result the transmitters S and for a brief while 1 are keyed. Transmitter S however, is unable to act upon the aerial by way of the blocked tube 41. The transmitter furnishes by way of the open tube 21 an impulse by way of transformer 24 into the antenna. As a result, by way of transformer 22, the tube 26 is made conducting, condenser 25 is charged, and tube 21 is blocked. On the other hand, by way of transformer 23 the tube 37 is made conductive, condenser 35 is discharged and tube 31 released. At the beginning of the signal neXt following, the transmitters S and S are keyed by way of tube 6. However, since only the tube 31 is unblocked, it is only S which can act upon the antenna by way of transformer 34. As a result, tube 31 is blocked by way of transformer 32, while tube 41 is blocked by way of transformer 33, and so on. Each impulse by way of a transmitter causes unblocking of Condenser 25 is discharged so the tube located above the next transmitter so that upon each subsequent impulse invariably only the following transmitter is able to act upon the antenna.

For the reception of signals sent out according to the present addition patent application, recourse may be had to the arrangement shown in Figure 3.

From the antenna 5 are fed the amplifiers V V V VA which are tuned to frequencies f1, f2, f and i The amplified current flowing in the output circuit of V and V acts upon the grid 6 blocked by the grid biasing potential so that in the presence of an A. C. potential in the grid of this tube a plate current flows across the winding 7. The amplifiers V and V act upon tube 8 blocked by grid biasing potential so that in the presence ofagrid A. C. potential in this tube, a plate current will flow through winding 9. A current flowing through the winding 7 causes the recording means to be cut in circuit by arrangements well known in the prior art, while currentthrough winding 9 causes disconnection of the recorder.

The amplifiers V V V and V; as shown tube 50 arranged in the rear of the first arm I plifier stage sets up a fall of potential across the terminals of a resistance 51, and this fall of potential is applied to a tube blocked by the biasing potential with such poarity that the blocking condition ceases. The plate current of tube 52 flows through a resistance 55 whose fall of potential is fed as a supplementary grid biasing potential to the input amplifier tubes 56 and 57. In parallel relation to resistance 55 is .a condenser 58. The internal resistance of tube 52, the resistance 55 and the capacity 58 are so chosen that the charging of 58 occurs by way of tube 52 inside a length of time which is about the same as the duration of a transmitted impulse, whereas the discharge or draining of the condenser 58 by way of resistance 55 with the tube 52 being blocked requires a length of time equaling roughly the duration of the echo signals which are to be suppressed. After absorption of an impulse, each of the amplifiers V V V V for the durat on of the echo, as a result has an increased grid biasing potential acting upon its input amplifier tubes and thus has a markedly dimlnished sensitiveness. As a resultsuch echo signals as may be produced will never be able to reach the rectifier tubes 6 and 8 of Figure 3, while for each fresh impulse a perfectly effective amplifier tube will be made available.

What we claim is: D

1. A system for eliminating the disturbing spread of signals in short wave telegraphy which comprises a transmitter having thereat a message subject from which signals are to be produced, means to produce from themes sage subject signals of different intenslties to quency value, a receiver at each desired point of message reception, means at the points of reception for utilizing one of the transmitted signals to initiate at the beginning of each time period of reception continuing recordings, means for utilizing another of the transmitted signals to cause at the beginning an interruption of the continuity of therecordings and an initiation of an interruption period corresponding to the absence of recordings so as to duplicate the record from which the signals were initiated at the point of transmission.

2. In a signalling system, a plurality of sources of differing transmitting frequencies, means responsive to pro-recorded marking signalling indications for causing a plurality of said sources of transmitting frequencies to become operative in sequence, means responsive to spacing periods in said pre-recorded signalling indications for causing a plurality of differing transmitting frequencies to become operative in an alternate relationship with respect to the operative frequencies of signal indications, and means for transmitting in sequence the said frequencies indicating markings or spacings of pre-recorded signals.

3. A system for eliminating the disturbing spread of signals in short wave telcgraphy which comprises a transmitter, means to pro- 1 duce control signals of pre-established diftering intensities representative of marking and spacing periods on a message subject, means for generating an even number in excess of two differing carrier frequencies, means for cyclically causing the transmission of a different generated frequency at each successive period of different control signal intensity, means for cyclically and individually transmitting other generated frequencies at time periods corresponding to different control signal intensity, a receiver responsive to each of the plurality of transmitted frequencies, means forming a part of the receiver for causing individual frequencies of the transmitted signals to initiate at the beginning of each time period of reception continuing recordings and means for causing other individual frequencies of the transmitted signals to cause interruptions of the recordings produced by the other of the received signals.

4. In a signalling system, a plurality of sources of differing transmitting frequencies, a source of control signals of two different fixed intensity values which represent marking and spacing periods of recorded marking signalling indications, means for causing a predetermined plurality of said sources of transmitting frequencies to become operative in accordance with one intensity of the control signals, means for causing a second plurality of the sources of transmitting frequencies to become operative for a different intensity of control signal, means for limiting the operation of any of the sources to a single source at any instant for each control signal intensity, and means for cyclically and Se quentially switching the operative periods between the several sources for each change in control signal intensity, and means for transmitting the selected frequencies to desired receiving points.

5. The method of transmitting signals from a black and white image subject which comprises producing electrical image currents of intensities proportionate to the blacks and whites of successive elemental sections of the image subject, generating a plurality of separate and distinct frequencies, sequentially connecting each of the sources of said generated frequencies with a transmission channel, and changing from one to another of the generated frequencies in the sequence at each time period corresponding to a change in image current intensity representative of a change between black and white on the subj ect to represent one signalling condition and between a second plurality of signalling frequencies in sequence interspersed with said first named signalling frequencies to indicate the opposite signalling condition, receiving the said transmitted signalling frequencies and causing the beginning of receipt of signals of each of said frequencies to produce continuing marking and spacing effects.

FRITZ SCHROTER. WILHELM RUNGE.

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