US2438903A

US2438903A - Pulse communication system employing pulse frequency reduction for signaling

Info

Publication number: US2438903A
Application number: US505778A
Authority: US
Inventors: Edmond M Deloraine; Donald D Grieg
Original assignee: Standard Telephone and Cables PLC
Current assignee: STC PLC; Federal Telephone and Radio Corp
Priority date: 1943-10-11
Filing date: 1943-10-11
Publication date: 1948-04-06
Anticipated expiration: 1965-04-06
Also published as: BE473141A; CH262447A; GB600261A; CH276277A; FR57499E; FR946811A; GB583629A; BE481274A

Description

Apnl 6, 1948. E. M. DELORAINE ETAL 2,438,903

PULSE COMMUNICATION SYSTEM EMPLOYING PULSE FREQUENCY REDUCTION FOR SIGNALING Filed oct. 11, 1945 `TIME A T OHNE Y Patented Apr. 6, 1948 PULSE .COMVIUNICATION SYSTEM EMPLOY- ING PULSE FREQUENCY REDUCTION FOR SIGNALING Edmond M. Deloraine, New York, and Donald D. Grieg, Forest Hills, N. Y., assignors to Federal Telephone and .Radio Corporation, New York, N. Y., a corporation of Delaware Application October 11, 1943, `Serial No. 505,778

This invention relates to signaling systems and more particularly Vto signaling systems adapted for use in regular intelligence communication systems.

In vthe normal telegraph and telephone ycommunication systems using-amplitude or frequency 6 Claims; (Cl. 179-15) modulation, particularly carrier communication A systems, the transmission of ringing and the like signaling has generally constituted a relatively complex problem. With the use of `modulated impulses for transmission Vof intelligence, simplied forms of signaling devices are readily possible. Such arrangements are broadly disclosed in the copending application of E. M. Deloraine, entitled Communication and signaling system, led on October 4, 1943, lSerial No. 504,881.

It is an object of our invention to provide a signaling system vof a novel character for use with modulated impulse communication systems.

It is a further object of our invention `to provide the signaling system for use in impulse modulation systems wherein the signal receptive means maybe connected directly to the output of the demodulating receiver.`

Other objects of our invention and specific features thereof will become apparent from a reading of the particular description of an embodiment thereof made with reference to the accompanying drawing, inwhich:

Fig. 1 is a block circuit diagram of a system embodying our invention; and

Fig. 2 is a setof curves used in explainingthe operation ofthe system of Fig. 1.

In Fig. 1, a multiplex impulse communication system is diagrammatically shown comprising a source of synchronizing Waves supplying Vcontrol Waves to impulse modulator and through phase Shifters I4 and I5 toother impulse modulators I2 and I3. It `should beunderstood that while only three channels are'shown in the present system, other modulators may he provided to furnish as many -channels as the line can properly carry. 'The `outputs from impulse modulators |I, |2 and f|3 are applied to a common line I8, preferably a coaxial line or other high frequency carrier line.` -In 'place of a transe mission line, radio transmission may be `used if desired. These impulses because-of phase Shifters I4 and I5, are inter-leaved `one with the other to provide a resultant Wave of `

impulses

2 and 3, as shown in curve a ofEig. 2.

These impulses areapplied `to a synchronizing control oscillator or other means of any suitable type 20 and to `channel selectors 2|, 22 and 23. At the same time, 'synchronizing control output 2 is applied to channel selector 2| and over phase shifters 24 and `25 to channel selectors 22` and 23, to select the desired channelbefore demodulating the received impulses in the normal manner. The selected impulses from channel selec,- tor 2| are applied over line 26 and condenser 21 to the voice or other frequency reproducing demodulating apparatus 3|. Similarly, the output from each `

channel selector

22 and 23 is applied over lines 26A, 26B and condensers 21A,

21B, respectively, to other demodulators $32, 33.

The impulses I, 2 and 3 are modulated, preferably in time position, in accordance with the sound signals to be transmitted. Thus, the sound signals derived from the impulses are applied at the output of demodulators 3|, 32 and 33. It is clear that Vpulse amplitude modulation may be used instead of time modulation, if desired, in which case the Vdemodulators will serve to reproduce the sound frequency envelope directly. Thus, in normal operation, the separate channels are used for separate communications.

-In accordance with our invention, when it is desired'to signal to a Vreceiving station to indicate that intelligence signals are to be transmitted or for some other purpose, a frequency divider is provided 4to reduce the number of `impulses in that; channel to a ringing or signaling frequency. To this end, turning first to the channelusingmodulator and channel selector 2|, We provide a frequency divider I6 controlled by synchronizing source -|0. This frequency divider comprises a square Wave generator VIta', and a mixer and clipper Ib to provide a Wave of the form such as 30 shown in curve b which is added to the impulse train serving to elevate every fourth impulse from the output koin-icdulator I These elevated impulses are then clipped at the level indicated by clipping line 3|a so that only every fourth impulse from modulator is applied to line I8.

It should be understood that the factor of frequency division is shown only by Way of illustration. Normally, the number of impulses applied to the line would be in the order of twelve thousand per second. It would usually be preferable then to reduc-e the frequency to some value depending on the ringing connection used. Where the output of the demodulator is `used to supply theringing energy a value such as or 300 pulses or cycles per second would he used, so that the frequency division normally would be much greater than-that shown in itssimpllied form for purposes of illustration.

and since these are at a low frequency level as indicated by the elevated impulses of curve c, the output of channel selector 2I will provide this low signaling frequency as indicated by the impulses above the clipping level 33a of curve c. Condenser 21 preferably is selected so that it does not pass this low frequency and all the low frequency is therefore shunted over low pass-filter 28 to signaling buzzer 29. Thus, the signaling unit may be connected directly across. line 2li..f

Instead of providing a separate low pass filter there are provided in said train substantially only impulses recurring at a given low cadence frequency, receiver 'means for receiving said .impulses, and signal means responsive to said impulses of said low cadence frequency coupled directly to said receiver means for producing said signals, said means for effectively selecting said impulses comprising a frequency divider includ- Ving a square wave generator, a mixer and a clipper, means coupling the output of said generator to saidmiXer and clipper, and means for selectively inserting and removing said frequency divider from the circuit.

. ,-2. A transmission system comprising a source of impulses for producing impulses having a normal spacing providing a cadence frequency for saidimpulses higher than the frequency of in- 28, buzzer 29 may readily be made of such frequency characteristics 'that it will respond to these low frequency-signals but will serve as a choke to the normal higher frequencies.. Alternatively a second means of utilizing the signalling characteristics of the device is to allow-the audio output of demodulator .3l rather than the direct pulses to energize relay 29. Under this condition an audio tone corresponding to the divided pulse frequency will be obtained at the output of the demodulator and Vwhich is of suiiiciently low frequency to be passed by filter 28 and excite the buzzer 29. For this type of operation, connection is made to the buzzer 29, from the output side of demodulator 3 I.

It is thus clear in our invention that we have provided a very simple form of signaling system. It is only necessaryto operate switch I1 to a position including in series frequency divider I6 in order to signal to demodulator 2|. When the signaling is not taking place, switch I'I is returned to a position to directly connect modulator II to line I8 withoutthe frequency divider Iii in series.

In order similarly to signal from modulators I2 and I3 we provide frequency dividers IBA and IEB connectable into the line by means of switches-IIA, IIB, respectively. The signaling frequencies produced by frequency dividers IBA and ISB are selected in

demodulators

22 and 23, respectively, and applied to the respective outputs at 28A, 29A andr28B, 29B t-o signal these other selected stations. y It should be noted that a single frequency divider may be used for all channels in place of the individual dividers by providing the proper switching arrangement.

It is clear vthat any desired form of frequency divider may be used in place of the type diagrammatically illustrated. Furthermore, other forms of signaling equipment than the simple buzzers may be provided. if desired, at the receiving end.

While we have described above the principles of our invention in connection with specific apparatus, and particular modifications thereof, it is to be clearly understood that this description is made only by way of example and not as a limitationon the scope of our invention as set forth in the objects of our invention and the accompanying claims.

What is claimed is: f

1. In a transmission system of the type wherein intelligence is transmitted by modulation of a train of impulses repeated at a cadence above the highest frequency of said intelligence, a system of signaling comprising means for effectively selecting certain discrete impulses of said .train at regularly recurring intervals, whereby telligence normally transmitted thereby, a transmission "medium for said impulses, receiver means for receiving said'impulses after transmis- -sion over said medium, a frequency divider for reducing said cadence frequency to alower signal frequency cadence,A means for selectively inserting said frequency divider between said impulse source and said medium, and means in the .output of said receiver means responsive to said signal cadence frequency impulses to produce a signal indication at said receiver.l 1 Y Y 3. In a communication system of -the Atype wherein intelligence is transmitted from a transmitter through a transmission medium in the form of a train of modulated impulses repeated at a cadence above the highest frequency of -said intelligence to a receiver; a signaling arrangement comprising a selector for selecting discrete impulses of said train at regularly recurring intervals whereby there is provided at the output of said selector a train of impulses recurring at a cadence equal to the periodV of a lower frequency, means for selectively coupling said transmitter either directly to said transmission medium or through said selector to said medium, and signal means at said receiver responsive to said impulses of said lower frequency coupled to said receiver for producing said signals.

4. A transmission system comprising a source of impulses for producing impulses having ancrmal spacing providing a cadence frequency for said impulses higher than the frequency of Vintelligence normally transmitted thereby, a transmission line for said impulses, receiver means for receiving said impulses after transmission over` said line, a frequency divider for reducing said cadence frequency to a lower signal frequency cadence, means for selectively inserting said frequency divider into said line, and means in the output oi said receiver means responsive to said signal cadence frequency impulses to produce a signal indication at said receiver.

5. In a multi-channel communication system wherein communication is carried on between a plurality of transmitters and a corresponding plurality of receivers over a common transmission medium, each of said transmitters providing a train of impulses spaced apart by a regular time interval to produce a cadence frequency above the highest frequency at which intelligence is normally to be transmitted, and each of said receivers serving to receive and demodulate the corresponding train of impulses from the transmitters and apply it to an individual output line, a system for selectively signaling from any one of said transmitters to the corresponding receiver comprising a frequency divider means for each said transmitter to provide for reduction of said 5 cadence frequency to a signal frequency, means for selectively connecting each frequency divider in the output of its corresponding transmitter, and signal responsive means tuned to respond to said signal frequency, coupled to the output 5 .transmission line at each receiver.

6. A multi-channel communication system according to claim 5 further comprising a synchronizing wave source at the transmitter terminal and a, second synchronizing source at the receiver 10 terminal for normally synchronizing the operation of said transmitters and said receivers, and means coupling said synchronizing source at said transmitter terminal in phase controlled relation to said frequency dividers to synchronize 15 REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATES PATENTS Number Name Date '2,204,375 Morrison June 11, 1940 2,213,941 Peterson Sept. 3, 1940 2,326,584 Van Zeist 1 Aug. 10, 1943 2,048,081 Riggs July 21, 1936 2,172,354 Blurnlein Sept. 12, 1939 1,484,405 Oswald Feb. 19, 1924 1,532,336 Nottage et al. Apr. '7, 1925 2,263,369 Skillman Nov. 18, 1941 FOREIGN PATENTS Number Country Date 418,525 Great Britain Oct. 26, 1934