US2352918A - Two-way telephone and telegraph system - Google Patents

Description

July 4, 1944.

J; E. SMITH Two-WAYJTELEPHONE AND TELEGRAPH SYS-TEM Filed oct. 50, 1.942

- propagation constant.

monica Joly 4, 1944 J. Ernest smith, Jackson Heights, N. Y., nssignor' to Radio Corporation of Americaa corporation of Delaware Application october 3o, 1942, serial No. 463,883

' 12 claims. (ci. 179-4) This invention relates to two-way telephone andtelegraph systems, and more particularly t0 a device for improving the :transmission characteristics of a combined telephone and telegraph circuit., The improvements havefor their principal object to minimize the effectsof outside 4'interferenceupon telephone andy telegraph channels and to overcome the effect of a variable In the past, where the line consisted of a twistthe received -signal varies greatly with weather conditions, theinfluence of the earth's magnetic ileld. and induced noiseinterference. Where a telegraph signaling system is to be combined j ed pair of conductors, it has been.. found that with a telephone circuit, it has been a common i.

practice lto terminatel the transmission line at both ends by a transformer havingga center-tap through which telegraph signals might be sent and received. The telegraph signals would thus be conveyed over the two conductors of the twistled pair the same as if they were a single conductor. The telegraph apparatus at each station lwould be grounded, thus completing the telegraph circuit. The telephone circuit was operated in a conventional manner, voice signals being induced on the individual conductors of the twisted pair 1n phase opposition. The diiliculties encountered were not so much due to interfervence between the telephone circuit and the tele- Will preferably pass any frequency below 250 20.

lcircuit arrangement including apparatus units which are vsuitably combined at a single station and rendered operable both. for transmission and .reception of telephone and telegraph signals; and Fig. 2 shows a modified circuit arrangement.

Referring to Fig.- 1, I show therein a line I terminating in a transformer winding 2 which is inductively coupled to a winding 3 in the same transformer. A Ahigh-pass filter 4 is interposed between the transformer winding 3 and terminals 5 leading, say, to a telephone instrument having a microphone andan earphone. The characteristics of the filter I are preferably those .which will pass speech signalsabove a frequency of 250 cycles and will eifectually block any frequencies below 250 cycles. For telegraph signaling, a low-pass filter 6 may be used. This filter cycles.' o

The lters 4 and 8 are so designed that energy maybe fed'into them from either end. They will,'therefore, be uniformly eflicient fortwoway communication work. So far as the transformer winding 3 is concerned, this is connected l to the right hand terminals of filters 4 and 6 in graph circuit, as they were due to unstable lground return effects such as might'be produced by the earths magnetic field. Furthermore, the emciency of the-telegraph circuit was limited by a high degree of attenuation of the received signals. The telegraph system was `also subject to erroneous operation due to induced noise interference on the line.

' Accordingly, it is an object of my invention to provide a two-way communication system having a twin conductor circuit over which telephone and telegraph signals may be transmitted simultaneouslv, and whereinfthe .signal propagation shall be rendered relatively independent of outside influences.

Itis another object of my invention to provide a system of the class describedv whichovercom'es the adverse effects of attenuation in a long line 'and which requires a minimum vof terminal apparatus for accomplishing this result.

Other .objects and advantages of my invention will be made apparent inthe description to follow. This description is accompanied by a drawing, in which: Fig. 1 shows in diagrammatic form a preferred parallel. The left hand terminals of filter B are branched. One branch leads to the input side ofl an amplifier limiter device 'I which is useful for amplifying the received telegraph signals. 'I'he output side of the amplifier 1 is again branched and leads to two parallel-connected filters Q and 9. Filter 8 has a high-pass characterlstic ,for passing frequencies above 125 cycles,

/e. Filter 9 has a low-pass characteristic and passes frequencies below cycles, for

for examp example.

'I'he telegraph signals to be transmitted and received will preferably be composed of two distinguishable frequencies.- For the sake of illustration, the marking frequency is indicated -as cycles, while the spacing frequency may be 100 cycles. Accordingly, the marking frequency will be passed by filterV 8 and after rectification in'the rectifier i0, the rectified energy maybe caused to traverse one winding il of a polarized relay. 'I'he two windings il and i2 of this relay are terminated in acommon ground connection. Winding i2 is fed with rectified energy through the rectifier I3 in the output circuit of filter 9.

The tongue I l of the polarized relay cooperates with stationary contacts oneof which may be dead, while the other contact i5l is fed with'a positive potential from any suitable source. The i' relay tongue I4 may be connected to the respontionary contact I5. In this manner a marking impulse is impressed upon the responsive means inthe receiving printer I6. As is well'known,

such responsive means may consist of selectorsv suitable for causing the printer to record characters corresponding'to a train of telegraphsignals.

The various terminal apparatus units thus far described are -used at either stationfor the reception of telegraph code signals. The transmitting apparatus is preferably the same at the two stations and will now be described.

A conventional code keyer I1 is. indicated as having five movable contacts I8 for composition of the well-known five-unit code signals. Such signals may be delivered by a manually operated keyboard or by a perforated tape sensing device. The code keyer also comprises a so-called startstop contactor 2li if desired. -In place of the code keyer,v as represented, a simple hand-operated telegraph key may be used, or more elaborate apparatus such as a synchronous signaling systern may be adopted if desired, the same as in multiplex telegraphy. In any case, the signals as transmitted may be characterized by two frequencies, say of 150 cycles for marking impulses, and of 100 cycles for spacing impulses.

A relay I8. has its winding connected between ground and a conductor which is alternately fed by positive and negative impulses in accordance with the permutational setting of the five code contacts I against positive or negative stationary contacts in the keyer -I1. In conventional stop-start five-unit code keyers, each five-unit code signal is always preceded by a spacing impulse and followed by a marking impulse. The start impulse is produced, therefore, by movement of the contact tongue 2Il'from its positive to its negative stationary contact in the keyery I 1. The tongue 2I of relay I8 responds to code keying by the unit I1 and thus feeds current of different frequencies to the output circuit 22. The marking and spacing frequencies are preferably derived .from two` separate oscillators 23 and 2l, each connected to a respective one of the stationary contacts which are associated with the relay tongue 2 I. One output terminal in each of these oscillators may be grounded if desired.

The signals are composed by the keyer I1 and as characterized for mark and space bythe osci1;

lators 23 and 24 may beapplled through a capacitor 25 to the input circuit of an amplifier 2l.

The output circuit for this amplifier is connected to a double-pole single-throw switch 21, this*l switch being closed when transmitting. The conductors 28 connect the upper terminalsof switch 21 to the left hand terminals of the lowpass filter 6. These signals are, therefore, ap-

- plied'to the transformer winding 3, now operating as a primary, and they are thus coupled to the terminating transformer winding 2 in the line I.

In place of the oscillators 23 and 2l, itis apparent that I may if desired utilize a single oscil-A lator, thel tuning of whichrnay be varied by a switching operation under control of the relay I8. In this way the invention may be carried out Avery simply by providing a certain fixed tuning for the closed tank circuit ofthe oscillator, and by switching on and off an added capacitance filter 6 has one of its terminals grounded and the other terminal is connected to a center tap on the winding 2a. The telegraph signaling channel is such, therefore, that the signals are transmitted co-phasally over the two conductors of the line I',-and ground connections are required at both. stations for the return circuit.

Since identical terminal equipment may be used at the two ends of the line, there is no need to describe other apparatus than merely that which exists for transmission and reception at one station. It is apparent also that for use of the telephone circuit, it is unnecessary to show the actual telephone equipment which would be employed, since that equipment may be of any conventional type.

While I have illustrated my invention and described its components and its mode of operation in accordance with only two exemplary embodiments, it is to be understood that I do not intend to be limited to the use of the equipment which is herein shown and described. I claim:

1. In a communication system, a two-way station comprising simultaneously operable telephone and'telegraph apparatus, a two-conductor ltnea high-pass filter offering a low impedance tothe useful frequency bandof telephone signal's,.a l'w-pass filter offering a low impedance phone set coupled to said line through said highpass filter, and telegraph signaling apparatus coupled to said line through said low pass lter,

` said telegraph signaling apparatus having frequency-characterizing means for distinguishing between the marking and spacing elements of outgoingcode signals and frequency discriminating telegraph signal responsive means adapted and arranged to accept and translate incoming code signals.

2. A two-way communication station according to claim 1, wherein said frequency discriminating means includes filters the input terminals of which are parallel-connected, said filters having cut-off points which lie between the characteristic marking and spacing frequencies of the incoming code signals.

3. A two-way communication station according to claim 1, wherein said frequency discriminating means includes a vhigh-pass filter for ac.

cepting the frequency of the marking code elements, and a low pass filter for accepting the frequency of the spacing code elements, the frequency bands passed by the last mentioned filters being mutually exclusive. and said responsive means including a polarized relay having oppos- 'ing windings each in circuit with the output terminals of one of these filters respectively, and means for rectifying the alternating current output from these filters, thereby to energize said relay windings with rectified potentials.

4. A system for composite telephony and telegraphy over a twin-conductor circuit, said system comprising filter means for passing telephone 'frequencies and for excluding telegraphic tone signal frequencies, filter means for passing said telegraphic tone signal frequencies and for excluding said telephone frequencies, the differtwo tone frequency oscillators in said transmitter, andkeying means operable to deliver tone signals from said oscillatorsl at alternate intervals corresponding to said marking and spacing code elements.

6. A composite telephone 'and telegraph system comprising a plurality of stations in each of which transmitting and receiving devices are coupled to a communicationchannel, the transmitting ldevices including separate telephone and telegraph instruments, and the receiving devices also including separate telephone and telegraph instruments, filter means appropriate to the circuits of saidtelephone instrumentsand arranged for two-way passing of voice frequencies between said telephone instruments and said channel, and other filter means appropriate to the circuits of said telegraph instruments and arranged for twoway passing of certain tone frequencies allocated to telegraph code signals, the frequency bands passed by the two said filter ,means being mutually exclusive, said telegraph transmitting instruments including means and a code rkeyer arranged to feed tone frequency energy of different predetermined fre.

quencies from said generating means through said other filter means to said channel, and said telegraph receivingapparatus having frequency selective means and rectiflers for translating said certain `tone frequencies into signaling code elements of marking and spacing significance.

7. A system in accordance with claim 6 and including an amplifier limiter device in circuit between said other filter means andv said frequency selective means.

8. A system in accordance with claim 6 and including a switch for disconnecting said tone-fre-l quency generating means from said other filter means during reception ofl telegraph signals from a remote station.

9. Apparatus for signaling by simultaneous telephony and telegraphy, comprising a communitone-frequency generating cation channel extending between two stations, telephone filter means at both stations for passing speech frequencies above a predetermined filter cut-ofi' point to and from said channel, said Vfilter means being reactively coupled to conductive elements in said channel, telegraph filter means at both stations for passing two tone frequencies which lie in a frequency band below said cut-off point, said telegraph filter means being interconnected through ground and through conductive elements in said channel, means at each station for generating and keying said tone frequencies, thereby to transmit intelligence, and translating means at each station arranged to accept incoming telegraph signals which are composed of marking and spacing ele,- ments differentiated by said tone frequencies, said translating means including frequency selective filters each of which is arranged to accept an appropriate one of said tone frequencies and to reject the other.

10. Apparatus' according to claim 9 and including a transformer at each station, one winding in each transformer being terminally connected to said telephone Afilter means and the other winding being'terminally connected to parallel conductors in said channel.

, 11.- Apparatus according to claim 9 and including avtransformer at each station, one winding in each transformer being connected across Y terminals at one end of each said telephone filter means, and the other winding in each transformer being center-tapped and being connected across two conductorsin said channel, the center-tap being connected to a terminal at one end o f the adjacent` telegraph filter means, and a' ground connection to the remaining terminal at the same end of said telegraph filter means.

12. The method of signaling by simultaneous telephony and telegraphy over a given communication channel, and by using said channel as a two-way system, which method comprises restricting speech waves as communicated to and from said channel to a band of frequencies above a predetermined filter cut-off point, restricting telegraph signals as communicated to and from said channel to two distinct tone frequency allocations both of which lie below said cut-ofi' point, generating said tone frequencies to represent the marking and spacing connotationsof signal code elements, and translating such signal code elements when received at a given station by filter discrimination between the two said tone frequencies.

J. ERNEST SMITH.

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