US2102435A - Receiving apparatus for communication systems - Google Patents

Description

Dec. 14, 1937. w. P. PLACE 2,102,435

I RECEIVING APPARATUS FOR COMMUNICATION SYSTEMS Filed March 26, 1957 Amplifiew Demodulaiop. BF? f f .7 ll 7 6 7 W1:

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HIS ATTORNEY the system is in working order.

Patented Dec. 14, 1937 PATENT oreicn RECEIVING APPARATUS FOR COMMUNI- CATION SYSTEMS I Willard P. ,Elace, Wilkinsburg, Pa., assignor to The Union Switch & Signal Company, Swissvale, Pa., a corporation of Pennsylvania Application March 26,

12 Claims.

My invention relates to receiving apparatus for communication systems, and particularly to receiving apparatus for communication systems operating on the closed circuit principler I shall describe one form of apparatus embodying my invention, and shall then point out the novel features thereof in claims.

A feature of my invention is the provision of novel and improved receiving apparatus for communication systems which operate on the closed circuit principle by virtue of a signaling current of a predetermined characteristic normally flowing in the transmitting circuit for continuously indicating during non-communicating periods thatv Other features and advantages of my invention will appear as the specification progresses.

Receiving apparatus constructed in accordance with my invention is normally conditioned for reception and is responsive to signaling current of a predetermined frequency for actuating an indicator, and the apparatus is automatically conditioned for reproducing the voice frequencies of a telephone current when such signaling current ceases. Discontinuance of the display of the indicator when not immediately followed by reception of a telephone message is a warning of a failure of the system.

Apparatus embodying my invention is especially useful for communication systems for railway trains where the movements of a train are governed in part, at least, in accordance with verbal instructions received aboard a vehicle of the train from a remote station, the communication current being transferred to such vehicle through the mediurn of train carried elements effectively coupled With wayside circuits. Preferably, the communication current is picked up by the train carried apparatus by virtue of an inductor mounted on a vehicle of the train in inductive relation with the track rails, the track rails being included in a wayside transmitting circuit. It will be understood, however, that my invention is not limited in its use to communication systems for railway trains, and many places will suggest themselves Where the apparatus will be 1937, Serial No. 133,214

is disposed for inductive relationship with a transmitting circuit, not shown. When the apparatus is installed on a vehicle of a railway train, the inductor coil 10 preferably is mounted on the vehicle in inductive relation with the track rails. The electromotive forces induced in the inductor coil IC in response to current flowing in theassociated transmitting circuit are applied over wires 2 and 3 to the input side of the filter BPF, the output side of which filter is connected over wires 5 and 6 with the input terminals of the amplifier-demodulator AD. A circuit controlling contact 4, to be referred to later, may be interposed in the wire 3. The filter BPF is of the usual band-pass type and is proportioned and adjusted to pass the frequency band of the communication current and to substantially suppress frequencies either above or below such band. For example, it has been proposed in communication systems for railway trains to employ the upper side band of a carrier current of 7000 cycles per second modulated with voice frequencies for telephone communication, and to use the equivalent of such carrier current modulated by a single predetermined voice frequency for signaling. Under such circumstances, the filter BPF would pass a band extending from 7500 to 9500 cycles, the voice frequency range being taken as extending from 500 cycles to 2500 cycles. For signaling, the current may be that of 7800 cycles, which is the equivalent of the upper sideband of the carrier of 7000 cycles modulated by the voice frequency of 800 cycles.

The amplifier-demodulator AD may be any one of several Well-known types for such devices, and I is shown conventionally only for the sake of simplicity. It is deemed sufficient for this application to point out that the amplifier-demodulator AD includes a normally active source of carrier current for mixing with the incoming communication current, and is operative to cause only the voice frequencies to appear in the output circuit of the demodulator, the local carrier and the other products of demodulation being suppressed and not appearing in the output circuit. On the assumption the communication current is of the frequencies referred to hereinbefore, then the ,voice band of frequencies extending from 500 to 2500 cycles per second would appear in the output circuit of the demodulator when telephone current is picked up by the inductor coil IC, and the single predetermined frequency of 800 cycles per second would appear in the output circuit when signaling current is picked up by the inductor coil IC.

The amplifier-demodulator AD is provided with a normally closed output circuit including a resonant circuit and a winding operatively associated with a loud speaker or telephone receiver. As here shown, the resonant circuit is of.

the parallel resonant circuit type consisting of an terminal of the resonant circuit is connected over V I output circuit is not large at the voice band of frewire 1 with one output terminal of the amplifierdemodulator AD, and a mid terminal of the inductorL is connected'over wire l0, voice coil 9 of loud speaker LS and wire 8 with the other output terminal of the amplifier-demodulator. The res-v onant circuit consisting of, inductor L and condenser vCL is proportioned for resonance'at the voice frequency corresponding to the predeter mined frequency of the signaling current. When;

the 'slgnaling current is of the frequency assumed hereinbefore for the purpose of illustration, the resonant circuit is tuned for resonance'at 800 cycles per-second. Consequently, a. currentof relatively large amplitude-of 800 cycles persecond flows in the output'circuit in response to the signaling current picked up by the inductor coil 10 and supplied to the amplifier-demodulator The parts are further so proportioned "and the :terminal of inductor L, to which wire 10 is connected, is so positioned that the impedance of the quencies, and the winding 9 is effectively.infiu-. enced when the telephone current is picked up by the inductor coil IC and supplied to the amplif ler-demodulator. 7

n A portion of the winding of inductor L is connected across-the input terminals ,of a full wave rectifierv H, the output te'rminalsof which are connected with-the winding 12 of arelay R. It follows that the relay R is effectively energized by rectified current and pickedup in response to the signaling current flowing in the output circuit of the amplifier-demodulator, but that the relay is deenergized and immediately releases when the signaling current ceases.

The relay R controls a first indicator here shown in the form of a lamp B, a second indicator here shown in the form of a bell l4, and, the field winding l5'of the loud speaker LS. The indication lamp I3 is illuminated bycurrent supplied over a simple circuit including the B terminal of any convenient source of current such as a battery not 'pick up of relay R, the circuit being closed during the interval the back contact I! and the front contact 20 are both in engagement with the transfer contact I 8, as will be readily understood by an inspection of the drawing. 7

The operation of the'app'aratus is as' follows. 7

Under normal conditions, that is, during non-telephone periods, signaling current is continuously supplied to the transmitting circuit by apparatus at an associated remote station, and the electromotive force induced in theinductor coil IC is of the frequency corresponding to the frequency of the signaling current. This frequency of the electromotive'force falls within the pass band of the filter BPF, and hence the electromotive force is demodulator, and which latter frequency is the resonant frequency of the resonant circuit consisting of inductor L and condenser CL. Consequently, during reception of-signaling current the relay R is effectively energized and picked up by the rectified portion of current passed by the.

rectifier ll. With the relay, R picked up to close front contact 16, the lamp I3 is illuminated to indicate the receptionbf signaling current. In other words, the lamp [3, when illuminated, indicates that the transmitting circuit and the receiv ing apparatus are in working order. 7

i When the signaling current is interrupted, the relay R is deenergized and at'once releases, the lamp I3 being extinguished when the front'con tact I6 is opened. During the release of relay R, the bell I4. is sounded when both the back contact Hand the front contact 20 are in engagement with the transfer contact l8, and'the belllaudibly'indicates the termination of the signaling current;' With the relay R fully-released; to close back contact lfl, the field winding I5 of the loud speaker L8 is energized and the loud V speaker is conditioned for reproductionof the voice frequencies of va current flowing in the voice coil 9. The electromotive forces inducedin' the inductor coil 1G by a telephone current flow ing in the transmitting circuit are passed by the filter BPF' to; the amplifier-demodulator and;

cause corresponding voice frequencies to 1 appear in the output circuit of thedemodulato'r, with the result that the telephone message is reproducedby the loud speaker 'LS. At

the termination of telephone communication,

the restoring of the apparatus to the normal condition. If no speech follows the extinction of the lamp I 3, then the operator would know that the system is out of order and may take- 7 Whatever steps are necessarysi A portion of the winding [2 of relay R is short-circuited over a back contact 2| of the relay and the relay is provided with slow pick-up characteristics. Therelay R is preferably slow to pick up so that occasional current of the predetermined voice frequency of the signaling current which may pass through the rectifier to the relay R during reception of telephone current does not energize the relay for a suflicient period to pick up the relay and interrupt the operation of the loud speaker.

7 It is to be understood that receiving apparatus and transmitting apparatus may-be provided at the same station and two-way communication may be carried on. It is understood, of course, that thetransmitting apparatus at one station does not interfere with the operation of J the receiving, apparatus at the same station. This implies different frequencies, different paths for r the transmitted and received currents, or any other suitable well-known means. As 'here shown, the contact 4 would be operated either" Although specific frequencies have been used in illustrating the invention, it will be understood that the invention is not limited to these frequencies and other frequencies for the communication current may be selected if desired. As a matter of fact, the frequency of the signaling current may be outside of the voice band.

In the foregoing description, I have referred to the signaling current as being used primarily to check that the system is in Working order. It is clear that the signaling current may also be used for code signaling by providing apparatus at the remote station effective to periodically interrupt the signaling current in accordance with a prearranged code. Under such circumstances, the relay R and the indicators l3 and I would be operated in accordance with the prearranged code.

Although I have herein shown and described only one form of apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. Receiving apparatus for communication systems comprising, a demodulator capable of demodulating a carrier telephone current and a signaling current equivalent to the carrier modulated by a predetermined frequency, a parallel resonant circuit proportioned for resonance at said predetermined frequency, a loud speaker, a first winding associated with the loud speaker, means to connect said resonant circuit and said first winding across the output terminals of the demodulator to form an output circuit for the demodulator, a relay, means to connect a winding of the relay with said resonant circuit to energize the relay in response to such signaling current supplied to the demodulator, and circuit means including a back contact of the relay and a second winding associated with the loud speaker as well as a current source to condition the loud speaker as required for reproducing the voice frequencies of the current flowing in said first Winding in response to such telephone current supplied to the demodulator.

2. Receiving apparatus for communication systems comprising, a demodulator capable of demodulating a carrier telephone current and a signaling current equivalent to the carrier modulated by a predetermined frequency, a parallel resonant circuit proportioned for resonance at said predetermined frequency, a loud speaker, a first winding associated with the loud speaker, means to connect said resonant circuit and said first winding across the output terminals of the demodulator to form an output circuit for the demodulator, a relay, means to connect a winding of the relay with said resonant circuit to energize the relay in response to said signaling current supplied to the demodulator, an indication circuit including an indicator and a front contact of the relay to indicate the reception of signaling current, and other circuit means; including a back contact of the relay and a second winding associated with the loud speaker to condition the loud speaker as required for reproducing the voice frequencies of the current flowing in said first winding in response to said telephone current supplied to the demodulator.

3. Receiving apparatus for communication systems comprising, a demodulator capable of demodulating a carrier telephone current and a signaling current equivalent to the carrier modulated by a predetermined frequency, a parallel resonant circuit proportioned for resonance at said predetermined frequency, a loud speaker, a first winding associated with the loud speaker, means to connect'said resonant circuit and said first winding across the output terminals of the demodulator to form an output circuit for the demodulator, a relay, means to connect a winding of the relay with said resonant circuit to energize the relay in response to said signaling current supplied to the demodulator, an indication circuit including a lamp and a front contact of the relay to indicate the reception of signaling current, another indication circuit including a bell and a contact closed momentarily when the relay is released to indicate when reception of the signaling current ceases, and other circuit means including a back contact of the relay and a field winding of the loud speaker to condition the loud speaker for reproducing the voice frequencies of the current flowing in said first winding in response to reception of said telephone current.

4. Receiving apparatus for communication systems comp-rising, a demodulator capable of demodulating a carrier telephone current and a signaling current equivalent to the carrier modulated by a predetermined frequency, a parallel resonant circuit including an inductor and a condenser and proportioned for resonance at said predetermined frequency, a loud speaker provided with a voice winding and a field winding, means to connect said resonant circuit and said voice winding in series across the output terminals of the demodulators to form a closed output circuit for the demodulator, a relay, means including a rectifier to connect a winding of the relay across a portion of said inductor to energize the relay as long as such signaling current is supplied to the demodulator, an indication circuit including an indicator and a front contact of the relay, and circuit means including said field winding and a back contact of the relay to condition the loud speaker for reproducing the speech of such telephone current supplied to the demodulator.

5. In combination, receiving equipment normally conditioned for reception of a signaling current of a predetermined single frequency or a telephone current of the voice frequency range, a resonant circuit including an inductor and a condenser and proportioned for resonance at said predetermined frequency, a loud speaker provided with a voice winding and a field winding, means for connecting said resonant circuit and said voice winding in series across the output terminals of said receiving equipment to form a closed output circuit, a relay, means including a rectifier to connect a winding of the relay across a portion of the inductor to energize the relay when current resulting from reception of the signaling current fiows in the output circuit, an indication circuit including an indicator and a front contact of the relay to indicate reception of signaling current, and circuit means including said field winding and a back contact of the relay to condition the loud speaker when the signaling current ceases for reproducing the voice frequencies of the current flowing in the output circuit as a result of reception of the telephone current.

6. In combination, receiving equipment normally conditioned for reception of a signaling current of a predetermined single frequency or a telephone current of the voice frequency range, a resonant circuit including an inductor and a r current flows in the output circuit, an indication predetermined frequency, a loud speaker, provided I with a voice winding and a field winding, means for connecting said resonant circuit and said voice 7 winding in series across the output terminals .of said receiving equipment to form a closedoutput circuit, a relay, means including a rectifier to connect a winding of the relaytacross a portion of the inductor to energize the relay when current resulting from reception of the signaling circuit including an indicator and afront contact of therelay to indicate reception of signaling current, circuit means including said field winding and a back contact of the relay to condition the loud speaker when the signaling current ceases for reproducing the voice frequencies of the current flowing in-the output circuit'as a result of reception of the telephone current, and means terminal of the tuned circuitwith one output terminal of said receiving equipment and to conmeet a mid terminal of the inductor with the other output terminal of the receiving equipment over said winding to form a closed output circuit for the receiving equipment, a relay, means including a rectifier to connect a winding of the relay across a'portion" of said inductor to energize-said relay when current resulting from reception oisaid signaling current flows 'in'said output circuit, an indicator circuit controlled by said relay when energized to indicate reception of signaling current, and circuit means controlled by said relay when deenergized to condition said loud speaker as required for actuation of the "loud speaker by the first mentioned Winding when current resulting from reception of said telephone 7 current flows in saidoutput circuit.

8. Receiving apparatus for communication systerns comprising, a demodulator capable of demodulating a carrier telephone current and a signaling current equivalent to the carrier modulated by a predetermined frequency, a loud speaker provided with a voice coil and a field coil, a tuned circuit consisting of an inductor and a condenser and tuned to resonance at said predetermined frequency,'an output circuit connected with the output terminals of said demodulator and including said tuned circuit and said voice coil, a relay, means toconnect a windingof the relay across a portion of said inductor to energize the relay when'current of said predetermined frequency fiows in said 'outputcircuit, an indication circuit including a front con tact of the relay and an indicator as wellas'a current source to display an indication as long as such signaling current is supplied to the demodulaton'and another circuit including a back contact of the relay and said field coil as well as a current source to render the loud speaker responsive to the voice frequencies of current fiowing in said output circuit when the signaling current ceases and said telephone current is supplied to the demodulator.

9. Receiving apparatus for communication sys-' tems comprising, a demodulator capable of :de- 7 modulating a carrier telephone current and a sig-, 7

naling current equivalent to the carrier modulated by' a predetermined frequency, a loud speaker, a

tuned circuit consisting of an inductor'and a condenser and tuned to resonance at said predetermined frequency, an, output circuit connected with the output terminals of said demodulator and including said tuned, circuit and a first winding associated withthe loud speaker in series, a relay,

means to connect a winding of the relay across a portion of said inductor to energize the relay signaling current ceases for reproduction ofythe voice frequencies of the current flowing in said first winding inrresponse to telephone current supplied to the demodulator. V r V 10;" Receiving apparatus for communication systems comprising, a demodulator capable of: demodulating a carrier telephone current and" a signaling current equivalent to the carrier -modulated by a predetermined frequency, a loud speaker, a tuned circuit consisting of an inductor 30 and a'condenser and tuned to resonance at said predetermined frequency, an output circuit connectedrwith the output terminals of said demod- V ulator and including said tuned circuit and a first winding associated with the loud speaker in series a' relay, meansto connect a winding of the relay across a portion of said inductor to 7 energize the relay when current of said predea termined frequency flows in said output circuit 7 in'response to signaling current supplied tothe demodulator, an indication circuit including an indicator and a front contact of said relay to display an indication as long as signalingcurrent is supplied to the demodulator, and other circuit means including a back contact of the relay and. t

a second winding associated withthe loud speaker to condition the loudspeaker when such signaling ceases for reproduction of the'voice frequencies of currentfiowing in'said first winding in response 'to said telephone currentsupplied' to the demodulator. 7

11. In combination, receiving equipment normally conditioned for reception of communication current and including a demodulator capable of demodulating a given. telephone current and a signaling current of a predetermined frequency,

a normally closed output circuit connected with said demodulator and including an inductor and a condenser arranged in parallel and in series with another winding, said inductor and condenserprcportioned for resonance at the frequency corresponding to said. signaling current when demodulated, a loud speaker operatively associated with'said other winding but normally inactive, a relay, means including a rectifier to connect'awinding of, the relay across a portion of said inductor to energize the relay as long as signaling current is received, indication means 7 controlled by saidrelay' to indicate reception of the signaling current; and other means controlled I 7 by said relay'to render said loud speaker active and effective only'when said relay isdeenergized.

V 12. In combination, receiving equipment nor-f mally conditioned for reception of communication current and including a demodulator capable of demodulating a given telephone current and a signaling current of a predetermined frequency, a normally closed output circuit connected with said demodulator and. including an inductor and a condenser arranged in parallel and in series with another Winding, said inductor and condenser proportioned for resonance at the frequency corresponding to said signaling current when demodulated, a loud speaker operatively associated with said other winding but normally inactive, a relay, means including a rectifier to connect a winding of the relay across a portion of said inductor to energize the relay as long as signaling current is received, indication means controlled by said relay and including a lamp to visually indicate reception of the signaling current and a bell to sound a warning when the signaling current ceases, and other means controlled by said relay to render said loud speaker active and effective only when the relay is released.

WILLARD P. PLACE.v

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