US2412974A - Electric wave communication system - Google Patents

Description

E. M. DELORAINE ELECTRIC WAVE COMMUNICATION SYSTEM Filed sept. 11, 1943 v INVENTOR.

ATTQRNEY Patented Dec. 24, 1946 Fries ELECTRIC WAVE COMMUNICATION SYSTEM Edmond Maurice Deloraine, New York, N. Y., assignor to International Standard Electric Corporation, Delaware New York, N. Y., a corporation of Application September 11, 1943, Serial No. 502,007 In France August 29, 1941 (Cl. Z50-6) 12 Claims.

invention relates to transmission systems and more particularly to a transmission system in which signals are transmitted by modulated spaced impulses.

It has been proposed in modulated impulse transmission systems to use a mode of transmission consisting of producingat the beginning and end of a predetermined signal element a very short-impulse, the spacing in time between these short impulses defining the transmitted signal element at the receiver. A convenient means for receiving signals of this type may consist, for example, of a double stability trigger circuit which changes from one condition of operation in response to the iirst applied impulse and returns to its original condition in response to the next applied impulse. Thus, the receiving apparatus produces a rectangular impulse, the duration of which is dependent upon the spacing of the two impulses representing the signal element.

One of the disadvantages of such a system, however, resides in the danger of operation of the trigger circuit at the receiver as a result of parasitics or other line disturbances which may be equal in amplitude and of substantially the same width as the signal impulses.

A principal object of the invention is to provide a system of signal transmission by impulses which do notY have the above mentioned diiliculty.

Another object of my invention is t Provide a transmitter apparatus and receivers to produce the desired operational characteristics called for.

According to a feature of my invention, the beginning and end of each signal increment is marked by a combination of impulses instead of by single impulses. Because of the particular combination of impulses used, the correct signal may be readily distinguished from parasitic impulses which will not have the regularity of the combinations used. As a specific example, the beginning and end of each signal increment will be marked by two short impulses of the same amplitude, these two impulses being of the same polarity or of opposite polarities. Other recurrent combinations can Yreadily be thought of without departing from the scope of my invention.

This particular system of transmission retains the inherent advantages of the impulses modulation system in that relatively weak energy is needed for emission. The average power of the transmitter can be very low. Furthermore, this arrangement permits selective distribution of impulses to deine circuits because of the particular combination in specific channels. arrangement retainsthe average of high, signal- Also, this to-noise ratio since the amplitude of the incoming signal is not the controlling factor but rather the recurrence of the group of impulses identifying the signal element.

This system of transmission also permits multiplexing of signals by means of waves modulated by impulses Without necessitating ordinary frequency or amplitude filters. The various selected combinations of impulses may be assigned to separate channels and separation thereof can be made by receivers adapted to select the particular pulse combinations.

Transmission systems in which impulses are used at the beginning and end of each signal element are often provided to transmit only one of these impulses, the other one being reproduced locally to 'indicate the beginning or end of the signal element. This type of system can obvious-` ly be used in transmission systems ofthe type set forth in the present application as will be clear to those skilled in the art.

A better understanding of my invention and the objects and features thereof may be had by reference to the accompanying drawing, in which:

Fig. 1 shows an example of the energy wave present at a receiver in the known type of impulse transmissions;

Fig. 2 is an example of the energy present on a line operating in accordance with my invention showing two closely adjacent impulses for dening the beginning and end of each channel element;

Fig. 3 illustrates other impulse combinations for defining the signal elements;

Fig. 4 shows schematically a receiver circuit for responding to transmitted impulses of the type shown in Fig. 2; and

Figs. Band 6 show schematically two examples of transmitter circuits arranged to produce spaced impulse pairs in accordance with'my invention.

In order to simplify the description of the invention, the example used will refer to the rectrligular impulses as though they are dashes or dots of a telegraphic code system. It is clear, however, that the principles of my invention relate aswell to voice modulated impulses systems as wel1 as to telegraphic transmitting arrangements.

Fig. 1 represents the energy in a transmission line orv other transmission medium of the socalled double impulse type in which each signal element isV identified by an impulse at the beginning and end thereof. The distance between these impulses is generally long compared to the widthv of the impulses. In this curve A are shown 2,412,974 f M if the signal impulses 3, 4, and 5, `6 separated by intervals 1 and 8, respectively. These short impulses have been shown cross-hatched in order to make them stand out more clearly. At the same time, certain parasitic peaks 9 and I0 are present in the wave and these peaks being of similar amplitude and width to the signal impulses 3, 4, and 3 will tend to cause false operation at the receiver and therefore reproduce the incorrect signal. Thus, there would be produced in the receiver an impulse for 3 and 3, a Second rectangular impulse for 4 and IllA instead of the single desired rectangular impulse between impulses 3 and 4.

In order that Ithese impulses may be readily observed if recorded on a telegraphicreceiver or suitably interpreted in other apparatus, I pro-V vide signals Which may be readily distinguished from parasitics. For this purpose, the beginning and end of each rectangular impulse will comprise two or more short marking impulses applied closely adjacent one to the other. Thus, in Fig. 2, the beginnings and ends of the rectangular impulses are shown by 3', 3", 4', 4, 5', 5 and 6', B". The'parasitic pulses appear as S and Ill. It will thus be seen that the wanted signal impulses Yare easily distinguishable Yvisually from the recorded noise impulses even when high peaks such as 9' and I0 appear.

The particular form of identifying impulses shown in Fig. 2 is given only by way of example.

VIf desired, two' impulses of opposite sense, as

shown at II in Fig. 3, may be provided or a more complex combination of impulses, as shown at I2 in Fig. 3, may be used.

It should be clear also that these impulses may be directly adjacent one another or may be spaced slightly, depending upon the type of circuit used to produce them.

In Fig, 4 is illustrated a receiver circuit modied to respond to pairs of spaced impulses to the exclusion of single impulses of the same amplitude. The signals are applied to receiver I4 which produces in the output thereof pairs of pulses as shown, for example, at I3. These two impulses are applied in succession to grid I5 of tube I6. A second grid I1 is provided, this grid being normally biased so that the tube IE is nonconductive even though an impulse is applied to grid I5. Simultaneously with the application of the impulse to grid I5 the impulse is applied over a delay network I8 to grid I1. Delay network I8 is designed to produce a delay equal to the normal spacing between the two peaks of impulse I3.

This impulse in passing delay network I8 removes L the bias from I1 so that while this impulse is effective on grid I1, any impulse applied to I5 will be passed to the anode circuit of tube I6. Since the delay is properly chosen, the second impulse of any pair such as I3 will pass the tube providingthe resultant impulse I9. It will be seen, however, that the parasitics do not have this characteristic spacing and therefore will not be able to pass to I6. The impulses I9, after passing tube I6, are applied over transformer to a double stability circuit 2|. The iirst impulse serves to trigger this circuit to the upper position as shown at 22. The next successive impulse returns the double stability circuit to its original condition, as indicated at 23, thus reproducing therein a rectangular impulse corresponding to the spacing between the pairs of impulses received. These impulses may then be plated in a suitable-translator circuit 24 to reproduce the original transmitted signal.

It is clear that if three or more connected impulses are provided, it is merely necessary to provide other delay networks and other control grids in the tube such as I6 to take care of these successive delays.

The pairs of spaced impulses used at the receiver may be produced, for example, in a transmitter arrangement such as shown in the system of Fig. 5. According to this arrangement, a modulated wave source 3S is provided in which the normal modulated impulses of the type shown in Fig, l are produced. These impulses are then passed over trigger circuits 3| and 32 to a common output resistance 33 across which is .connected the transmitter 34. A delay network 35 is provided in the input circuit of trigger circuit 32. Thus, the impulse is passed directly from trigger circuit 3| to resistance 33 but because of delay network 35 the impulses from trigger circuit 32 is delayed a small amount so that a resultant double pulse arrangement is produced for application to transmitter 34.

rThe trigger circuits 3| and 32 may comprise any known apparatus, for example, they may include gaseous discharge tube of the typerknown under the trademark Thyratronf An example of a'transmitting apparatus suitable for generating the selected impulses for telegraphic signalling is shown in Fig. 6. In this system there is provided a high frequency source 40 which may, for example, be a sinusoidal generator. Energy from generator 40 is applied tothe control grids of gaseous discharge tubes 4|, 42 which are preferably biased so they will respond only 'to peaks above a predetermined threshold voltage. Potentiometers 43, 44 may be provided to control the threshold voltage of tubes 4| and 42. The wave from source 40 is applied to tube 4I withoutphase shift but in the circuit connected to tube 42 is provided a phase shifting arrangement consisting of inductance coil 45 and alternatively condensers 46 or 41 connected in circuit selectively by means oi key 48. Key 48 may be the usual telegraph key and transmits in its lower position pairs of signals spaced to correspond to dashes while in its upper position transmits pairs of signals with different spacing corresponding to dots. Condensers 46 and 41 are so adjusted that the delay will be diierent for one of the circuits then for the other to provide the different spacings.

Thus, in the output of tubes 4I and 42 will be produced pairs of impulses spaced apart by a distance representing signal elements such as dots or dashes of a telegraphic code.. The high tension voltage for operating tubes 4|, 42 may be applied across terminals 50. The output energy from the combined tubes may also be taken off, if desired, across the common cathode resist'- ance 5|. This output wave may then be applied to a pair of trigger circuits such as 3| and k32 of Fig. 5 over a delay network such as 35 so that similar operation to that shown in Fig. 5/is vaccomplished. Thusythe circuit arrangement of Fig. 6 may be considered as a special form of modulated wave source which may be used with the arrangement of Fig. 5 in place of source 30.

Although'my invention has been described in connection with particular examples, it is clear that it is not limited to this particular showing. The invention is not limited to telegraphic transmission systems as shown in the specific example but can be used in any case where the start or nnish impulses of a signal systemare produced at 'substantially fixed' impulses and are recreated at the receiver to reproduce I the original signal. Furthermore, each of the signals dening the beginning and end of va rectangular signal element can'be made in any desired form which is readily distinguishable from static or parasitic noises. The description therefore is not intended to be construed as a limitation of any invention assetlforth in the objects thereof and in the ap pended claims.

What is claimed is:

1. In a communication system of the. typev in which signal characteristics are represented by a series of iirst impulses modulated to represent the signal characteristics, said iirst impulses being spaced apart in time a large amount with respect to their duration, an arrangement for reducing the disturbing effects of interfering impulses comprising means for producing from each of said first impulses at least two indicating impulses spaced apart in time by a xed time interval which is small with respect to the spacing of said first impulses, receiver means for receiving said indicating impulses, and discriminator means in said receiver means for discriminating between impulses spaced apart by said fixed time interval and all other impulses, whereby only said spaced impulses may be used for signal indications.

2. A communication system according to claim l further comprising translator means for deriving the modulating signal from said received indicating impulses.

3. A communication system according to claim l wherein said discriminator means comprises first and second paths for said received impulses, blocking means normally blocking said first path so that signals cannot pass, delay means in said second path for delaying impulses lby an amount equal to said fixed time interval, and means for applying said delayed impulses to said blocking means to permit passage of ,impulses over said rst path during the time of application of each delayed impulse.

4. A communication system according to claim l where the means for producing two indicating impulses from each first impulse comprises two branch circuits, delay means having a delay equal to said fixed deiay in one branch circuit, means for applying said rst impulses to Said two branch circuits, and common output means for said two branch circuits in which are developed impulses from both branches.

5. A communication system comprising a modulated wave source, first and second branch circuits coupled to said source, a delay network having a predetermined time delay in said rst branch circuit, a first impulse producing circuit responsive to energy from said source coupled to the output of said delay network, a second impulse producing circuit responsive to energy from said source coupled to said second branch circuit, a common output circuit for said first and second impulse producing means for deriving pairs of impulses spaced apart in time by said predetermined time delay, each pair representing an increment of signal energy from said modulated wave source, transmitter means coupled to said common output'for transmitting said pairs of impulses, receiver means for receiving said transmitted pairs of impulses, discriminating means in said receiver for discriminating between pairs of impulses separated by said predetermined time delay and all other impulses, and translator means coupled to said discriminating means for reproducing the original modulatingsignal oi'- 5 wherein said modulated wave source comprises a radio frequency source, a pair of trigger tubes, means coupling said radio frequency source directly to one of said tubes, adjustable delay means adjustable into two delay conditions for coupling said radio frequency source to the other of said tubes, keying means for selectively adjusting said adjustable delay means into either of said two positions for signalling purposes, a common output circuit for said tubes to provide impulses with two selected time spacings representing telegraph modulations. and means for coupling said common output to said rst and second branch circuits. i

8. A transmitter system comprising a modulated Wave source, rst and second branch circuits coupled to said.source, a delay network having a predetermined time delay in said'iirst branch circuit, a iirst impulse producing circuit responsive to energy from said source coupled to the output of said delay network, a second impulse producing circuit responsive to energy from said source coupled to said second branch circuit, a common output circuit for said first and second impulse producing means for deriving pairs of impulses spaced apart in time by said predetermined time delay, each pair representing an increment of signal energy from said modulated wave source, and transmitter means coupled to said common output for transmitting said pairs of impulses.

9. A. transmitter system according to claim 8 wherein said modulated Wave source comprises a radio frequency source, a pair of trigger tubes, means coupling said radio frequency source directly to one of said tubes, adjustable delay means adjustable into two delay conditions for coupling said radio frequency source to the other of said tubes, keying means for selectively adjusting said adjustable delay means into either of said two positions for signalling purposes, a common output circuit for said tubes to provide impulses with two selected time spacing representing telegraph modulations, and means for coupling said common output to said first and second branch circuits.

10. A receiver system for receiving pairs of impulses spaced apart a predetermined amount in time, each `pair representing an increment of modulating signal energy in a modulated wave, means for receiving said pairs of impulses, discriminating means in said receiver for discriminating between pairs of impulses separated by said predetermined time delay and all other impulses, and translator means coupled to said discriminating means for reproducing the original modulating signal of said modulated wave.

11. A receiver system according to claim 10 wherein said discriminator means comprises rst and second receiver paths for said received impulses, blocking means normally blocking said rst receiver path so that signals cannot pass, delay means in said second receiver path for delaying impulses by said predeterminedamount, and means for applying said delayed impulses to said blocking means to permit passage of impulses over said first receiver path during the time of application of each delayed impulse.

12. In a communication system of the type in which Signal characteristics are represented by first impulses modulated to represent the signal characteristic, a method of reducing` the disturbing effect of interfering impulses which comprises producing from each of said first impulses at least two indicating impulses spaced apart by a fixed time 'interval which is small relative to the normal time spacing of said iirst impulses, receiving said indicating impulses, and discriminating between impulses spaced by said iixed time interval and other impulses by transferring said received impulses over iirst and second paths, delaying'said impulses in said second path by a time equal to said first time interval and applying said delayed impulses from said second path to said first path to render said iirst path conductive only during application of impulses from said second path.

EDMOND MAURICE DELORAINE.

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