US2407417A

US2407417A - Communications system

Info

Publication number: US2407417A
Application number: US568835A
Authority: US
Inventors: William S Halstead
Original assignee: Farnsworth Television and Radio Corp
Current assignee: Farnsworth Television and Radio Corp
Priority date: 1944-12-19
Filing date: 1944-12-19
Publication date: 1946-09-10
Anticipated expiration: 1963-09-10

Description

sept-10, 194e.

Filed Dec. 19, 1944 mZON Sept 10, 1946. w. s. HALSTEAD 2,407,417

I COMMUNICATIONS SYSTEM Filed Dec. 19, 1944 6 Sheets-Sheet 2 |NVENTOR ATTORNEY WILUAM s. HALsTl-:AD

Sept. 10, 1946.. w.`s. HALSTEIAD v 2,407,417

comaUNIcATIoNs SYSTEM E Filed Dec. 1'9, 1944 s sheets-sheet s sUPPl- Y MONITOR l RECEIVER PUSH KEY TO RECORD IMINUTE @l H CYCLE MoTOR FIGB WILLIAM S. HALSTEAD INVENTOR CD 9 ATTORNEY Sept. 109 1946 w. s. HALsTEAD ZWW COMMUNICATIONS SYSTEM'- Filed Dec. 19, 1944 6 sheets-sheet 4 EmOUmNTOPI T mDa .55200 /zmo .5n z 539.. d m Tsm ozmooma u E um@ T N @E Q AN R Hw m ri f sm n nv @E w: EJE M copos. md5 lwml@ kwam wl M mSz S, .w m. mi 5.52am W OS Hw mmf Sept 10,1946 w. sfI-IALs'rEAD 'I Y 2,407,417

COMMUNICATIONS SYSTEM Filed nec..19,`1944 e sheets-'sheet s v FIG. 5

WILLIAM s. I-IALSTEAD INVENTOR ATTORNEY Sept. 10, 1946. w. s. HALsTEAn COMMUNICATIONS SYSTEM 6 Sheets-Sheet 6 Filed Dec. 19, 1944 NGZ mmPP-MZ4NE. mZON INVENTOR ATTORNEY Patented Sept. 10, 1946 COMMUNICATIONS SYSTEM William S. Halstead, Purchase, N. Y., assgnor, by

mesne assignments, t

o Farnsworth Television & Radio Corporation, Fort Wayne, Ind., a corporation of Delaware Application December 19, 1944, Serial No. 568,835

This invention pertains to a system for establishing restricted-range radio 'communications Within a predetermined signaling zone or area, and more particularly to a signaling zone or area along a highway, railway track, or other delineated service area or zone Within the confines of which eiective radio signaling is to be conducted.

The invention also embraces means whereby the useful range of a radio transmitter is extended along a traffic lane in areas where signals from the radio transmitter would otherwise be ineffective, or Where communications between a central station and mobile units are to be channelized along selected lanes of traic or other delineated signaling zones.

VAn illustrative application of this invention is in the transmission of intelligence to vehicles proceeding through tunnels, steel bridges, city streets or other delineated areas where radio signal intensity from a remote space radio transmitter is subject to appreciableor effectively complete attenuation. It is also'possible, by use of the system of the invention, tinued radio service for vehicles without cessation of radio service on entering a tunnel, where normal space radio Wave energybecomes ineiective. This continuation of service may be accomplished without need for the operator of the vehicle to make any tuning adjustments in the vehicle receiver when passing from the effective signaling area of the space radio transmitter, such as a conventional broadcasting station, to the localized signaling area of the zone transmitting system Within the tunnel or other restricted area where the space radio signals cannot be received. Y

Another application of the system is in providing means, operable from a central control point, for selectively establishing communications with mobile units within a given trac communications zone, telephone lines or radio circuits being utilized in carrying intelligence from the central point' to a zone transmitter disposed adjacent the lane of traiiic Within which communications is to be effective, with signal energy from the zone transmitter bein-g held within the limits required in adequately serving the traiiic lanes with which it is associated.

Therefore, it is one of the objects of the present invention to provide means for effecting communications with mobile units by use of a primary radio transmitter serving a given area, and one or more zone transmitters disposed adjacent given lanes of traffic vor predetermined secondary signaling areas Within which signals from the prito provide a con- 22 Claims. (Cl. 179-2) mary radio transmitter are ineffective, each of said zone transmitters having means for restricting signal energy substantially within its associated traffic signaling area.

It is another object of the invention to provide means for extending the communications range of a primary radio transmitter, with respect to mobile units proceeding along a lane of traic,

i this extension in communications range being efneed for change in tuning of the mobile receiver in'movinugfrom the area where the signals from the primary radio transmitter are eiective into the area where signals from the secondary transmitter are effective.

It is an additional object of the invention to provide means with which intelligence addressed to mobile units may be received by the mobile units on entering a predetermined signaling zone along a lane of traffic, regardless of the frequency to which the receiver of the mobile unit may be tuned, prior to entrance into the signalingy zone, for radio paging or other services.

It is still another object to provide traffic zone transmitting means whereby prerecorded intelligence addressed to mobile units is automatically transmitted to mobile units on their entrance into a predetermined signaling zone along a lane of traffic, means also being provided for changing the prerecorded intelligence by remote control from a control point, all transmissions-on the traic lane being monitored by a receiver disposed adjacent the traic lane'and having means associated with its audio output circuit for effecting reproduction of the received signals at the central control point.

Another of the objects of the present invention is to provide means for signaling to radioequipped vehicles proceeding `through a tunnel or other conductively shielded enclosure.

Anotherobject of rthe invention is to provide meansfor retransmission of an effective radio signal, on either the same frequency or any other desired frequency, to radio-equipped Vehicles by means of a restricted-range carrier-wave signaling system extending through a tunnel or other conductively shielded enclosure.

Still another obiect of the invention is to provide means for broadcasting and/or disseminating special programs or instructions to radioequipped vehicles operating in a tunnel or conductively shielded area either on a specified frequency in the broadcast spectrum or regardless of the broadcast frequency to which the car radio mit voice signals to mobile units in said area,

and, simultaneously, while transmitting, to record the voice signals for subsequent repetitive reproduction at the conclusion of the recording cycle, the duration of the voice transmission period being substantially equivalent to the period of time required for completion of the recording cycle.

Another object of the inventio-n is to provide a remotely-controlled communications system to simultaneously transmit and record signaling intelligence, with means for obliterating a message previously recorded on the recording apparatus employed in the system, and means for automatically and repetitively transmitting the recorded intelligence within a predetermined signaling area or zone immediately subsequent to the termination of the recording cycle.

A further object of the invention is to provide a plurality of receivers, adjacent a lane of traflic, each tuned to one of the frequencies employed in a given signaling zone on said lane of traffic, With-means for connecting an amplier and a transducer to each or said receivers so that transmissions of different carrier frequencies on the trafc lane may be independently monitored at a central or remote control point.

A further object of the invention is to provide timing means controllable from a central control unit for determining the duration of the recording of intelligence which is to be transmitted to mobile units within a given signaling zone.

Other objects may be and may become apparent from a perusal of the disclosure, and it is t be understood that the invention is not to be limited except by the scope of the subjoined claims.

In the drawings:

Fig. 1 is a diagram of an illustrative application of the system of the invention as employed in providing a communicating service to mobile units in tunnels or in areas where normal radio facilities are ineffective.

Fig. 2 is a block diagram of a multiple-frequency traffic communications system employing a remote control system for functional `control of a traiiic zone transmitter-receiver combination.

Fig. 3 is a schematic circuit diagram of one form of traflic communications system providing automatic means for recording and retransmitting intelligence addressed to mobile units Within a given signaling zone along a lane of traffic.

Fig. 4 is a schematic circuit diagram of one form of a remote control unit for controlling the type of communications unit shown in Fig. 3.

Fig. 5 shows a remote control unit with one form of panel layout and switching controls.

Fig. 6 represents an arrangementl of equipment as employed in one application of the system of the invention.

In Fig. 1, the two tunnels i l are arranged to take care of tramo in opposite directions, each of said tunnels having a dual trafc lane. Moving vehicles on the above-mentioned trac lanes are represented by i2, IEA, IZB, and I2C.

In a transmitter room lll, at a convenient point, usually at one end of the tunnel are located the zone, or secondary, radio-transmitter I6 and the recorder-reproducer unit I?, where the latter is used. V

The radio frequency output from the radio transmiter i6 is coupled to the R. F. induction cables i9 and 2li which run the entire length of the tunnel and terminate in their respective terminating units 23 and 2li. The recorder-reproducer unit vil is coupled to the input of the radio transmitter l E.

The zone radio transmitter I6 and the recorder-reproducer unit Il are controlled by the remote control equipment located in a service building 2|, Vwhich may be at one of the tunnel approaches, or at any desired location.

A telephone line 25 is used for both the audio and control circuits between the remote control unit 2? in the service building 2l and the transmitter room It.

The remote control unit 2'! located in the service building has associated with it, a microphone 28, an electric phonograph unit 29, a radio receiver tt with its associated antenna 3l, and a loudspeaker 32. By means of control switches on the remote control unit 2l', it is possible to transmit direct from the microphone 28, or by means of the electric phonograph unit 29 over the zone radio transmitter l5. Also, it is possible to apply received radio signals from receiver 30 to the control unit 2l and thence to the transmitter it. Thus, in this system a signal from the originating, or primary, transmitter 34 with its associated microphone 35 and antenna 36 can be received on the zone radio receiver 3U and retransmitted over the zone radio transmitter I6.

The remote control switching system also contro-ls the recorder-reproducer unit l1 so that a message may be recorded on this device at the same time that it is being transmitted, the recorded message being thereafter automatically repeated over the tunnel radio system by means of the recorder-reproducer unit il until interrupted by the control operator when he desires to change the recording. Y

Fig. 2 is a block diagram of one form of the system for transmitting simultaneously on multiple frequencies. In the diagram a remote control unit di is located at a desired control point and has associated with it a monitor loudspeaker e2, a microphone 43, a phonograph unit 44, and a radio receiver 5 with its associated antenna 133.

The output from the remote control unit connects through the telephone line 46 to the transmitting control room Where are located a selective switching mechanism 68, a line transformer and transfer relays 59, a magnetic recorder-reproducer 5i, a group of

transmitters

52, 53, 54, and 55, and line coupling unit V5t. The radio frequency output from the line coupling unit 56 connects to a transmission line E8, said line extending the entire length of the tunnel and terminating in a terminating unit 69. Ineluded With the transmitters are four monitor receivrs'sl, s2, es; and sa,v

all having a commonpickup coil or antenna and withV their audio'- outputs connected tov the automatic selector switchf68- The antenna 65 is `coupled loo'sely to the transmission line signal energy' in lessv of the carrier frequency to VVwhich `the -vehiclereceivers are tuned. As an example, in the System described-'three ofthe transmitters and their' corresponding monitor'receiversY may betuned to 465, 262 and 175 kilocycles respectively and the remaining justed-'to fkilocycl'es'orfsome designated frequency assigned fior anyone* of the receivers may,v to a designated frequencyvem'loyed by mobile transmitters.A f -v By employing equipped mobile the 'system on entering the signal zone regardless of Ythe frequency to which the mobile receiver isv tuned through injection of the signals into the I.F.amplif`1er of the receiver.

vIn the operation of the system describedin liig.A 2 rthere are four transmitters, each-adjusted to a different frequencyY and transmitting simultaneously. The

the system described, a radiorecorder-reproducer 5| which continually repeats its message. The timing cycle of Ythe message may -b'e adjusted so that the completemessage will be received bya radio-equipped vehicle moving through `a tunnel at its maximum allowed speed during the time the vehicle is in the tunnel` The four monitor receivers 6|, 62, E3, and til have their outputs coupled to an automatic selector Iswitch 68 of any `well-.known type which may be controlled by means of any conventional dialing system vor means, the dialing mechanism may be located in the control unit 4| Vas Vwill be hereinafter described, said dial mechanism controlling the selective switching mechanism 18.Y Each of the abovementioned monitor receivers monitored by the loudspeaker control point by proper dialing.

The system also provides dialing or switching means which allows a direct transmission over the system from either the microphone 43, the phonograph unit 44or the rss-transmission of a message from the radioreoeiver 45.

In addition to the above-mentioned operations, switching, means are providedfor simultaneously transmitting and recording. 1

For the purpose oi showing the operation oi one formY of the radio transmitter and recorderreproducer unit, a vschematic circuit diagram of a single radio transmitter' and recorder-reproducer combination is shown in Fig. 3. In this diagramthe telephone line from theA remote control lequipment connects to the line transformer 16.- The line winding of Athe line transformer viii is dividedso that in addition to the 42 at the remote audiocircuit; the two control .circuits may be operated independent of each other. .Y

The radio frequencysection of the transmitter consists of a crystal oscillator; tube 18 and its associated output' circuit coupled throughthe capacitor 80 to the power Vamplifier tube A82 and 5B; and the monitor receiv-` ers' are each tuned toV acorresponding frequency transmitter and receiver vmobile operation. V"I-Iowever; if desired, be .tuned unit may'lreceive signa-ls from v transmitters. will normallytransmit information. from the magnetic tape' other automatic selecting.

may be individually erally used by vehicleradio receivers, itis-possible to receive radio signals-in tunnels regardlato;1 yofthe R. power amplifier The recorder timing.

by local control switchk |20B its associated output circuit. f The output inductance '84 'of the power ampliiieris coupled through the capacitor t'o the tran'smissionline 3l which! runs the entire length ofthe tunnel'and termi-'- terminating unit 38;." Thefaudio frequency section of the circuit consists ofa highgain amplifier stage 9E, the out-'l nates'at its far'end in a power amplifier or modulator tube S5.

.Thepower supply includes .a powerV transformer-198 andaV full-wave rectifier tube 9d with; its associated-lter. circuit 89A. The abovementionedV power; supply. provides heater currentv for all tubes anda source of E. M. F. for'tlie op-.i erationiof the .relay |13, the obliteratingcoilfml ,on .thev recorder-reproducer and plate vsupply voltage for .the audio Yand radio frequency tubes.'

:The recorder-reproducer i@ l or" vsound storage device, consists of an endless steel 'tape ori wire iii?. operating` onf rollers by means ci power supplied by the electric-motor |93, and is provided with a pickup coil |35 vwhich normally:

couples to the .grid input of speech input tube 90,' arecordingl coil. I which is provided for recording intelligence, and obliterating coil `il'l which removes, recordings previously made on. the steel tape. in the process `of'making a new recording, the O bliterating coil Iii? is energizedy by applying` voltage from `the power supplythrough thecontact ,|64 on the relay il.- which is energizedv during this process, resulting in niagnetically `erasingthe previously recorded messages. AThe recordingcoil is coupled, through a network rHi8 and -theycontact |09 on the yrelay ||3,.--to part ofv the outputwinding of the modulation transformer 91, resulting inra new recording on the tape-Whenspeech signals are impressed ongthe primary ywinding of the transformer Si' byl vs peechampliiier 96,.which also is the modu- 82. Thereeording cycle of the recorder-reproducen whichis d e-f termined automatically Y by timing motor-l mi, as hereinafter described, isusually of such duration that it will provide a complete transmission of,Av messagel over not-- moreV than the period of time that it takes for a moving Vehicle to travel the entire length of the tunnel or signaling zone at its maximum allowed speed. f

, A monitor receiver I6, isemployed for the'purposev ofpicking up andy monitoring the recorded transmissions( "I'he antenna ||0 connects to the monitor receiver` and ,is loosely coupled to the transmission line 8 1. f The output from themonitor receiver normally is coupled back intothe` telephone 1ine '|5 throughthe upper contactsof relay l|2 and line transformer I6 so that the rey-J., mote control point may have aV check on, or supervise thetransmissions made while the recorder-'1 reproducer` is operating in the reproducer position. Aloudspeaker I1 is also provided for. checking or supervising the transmissions locally in the transmitter-roomv 1 f x ,5 or vcycling.. motor. |20 Iris placed in .operation orV by energization'v of Aremotely fco'ntrolled. relay l andi'lclosu're .of :itsV contacts IA, as deter-i mined from theiremotezcontrol point; when-new audio component from the' couples to'this haii ofthe tube through Athe contacts l5. of the" relay. i |2`, when enei'gizedand the line-to-grid transformer 95.1- The mixer stage outputis coupled tothe'.

recordings are to be made. Cam |26, attached to the shaft |20A of motor |20, upon its movement when the timing motor is energized closes contacts 22 and thereby keeps the timing motor in operation until the cam makes one complete rotation, during which the steel tape |02 of the recording mechanism goes through one complete recording cycle. Concurrently, as contacts |22 are closed by cam |26, the contacts |2| are closed by cam |24, also on timing motor shaft |20A. Closure of contacts |2| applies energizing voltage to relay 3, thereby placing the electrical circuits of the recording condition. This is eiected by supplying voltage to obliterating coils |01 through relay contacts |04, as previously outlined, connecting signal voltage to recording coils |06 through relay contacts |09, and by grounding control grid 9| of tube 94, thereby rendering ineiective speech amplier tube 90, connected to the pick-up coil |05, which is used only during reproduction of recorded signals.

Thus, at the end of the recording cycle, as determined by the length of the steel tape or period of operation of timing motor |20, therecording operation, or cycle, is automatically terminated.

Control circuits are arranged in such manner that in normal operation, when no control signal is applied to the telephone line l5, the output of monitor receiver ||6 is connected to the telephone line through contacts ||5 of relay 2 and line transformer 16, while signals as re'- corded on steel tape |02 and as picked up by coil |05 are applied to the input of the speechV amplier 90, thereby modulating, through modulator tube 96, the radio transmitter of which power amplifier 82 is the R. F. output stage. If a new recording is to be made, a source of E. M. F.' is applied to telephone line T5, as Will hereinafter more fully be described, thereby energizing relay and starting timing motor which places the equipment in recording condition as previously described. In order to prevent feedback caused by signals from the monitor receiver H6 being applied to the telephone line 'I5A when the line is carrying signals from the remote control point to the recording mechanism |0| and transmitter during recording operations, contacts 89,

of relay I|3, which are closed when relay ||3 is i energized, apply energizing voltage to relay I2, thereby disconnecting the output circuit of mon-itor receiver ||6 from the line 15 through opening of the upper contacts of relay ||2. Closure of contacts ||5, which Y occurs when relay I2 is energized, then appliesA signal voltage from the remote control point to line-to-gri'd' transformer 95. Contacts 89 on relay ||3 are opened with energization of relay ||3 and remove a ground connection from lgrid S2 of mixer tube 94, thereby permitting signal from transformer 95 to be impressed on grid 92, causing modulation of the transmitter and applying the signals to recording coil |06. l

If a direct speech transmission is to be made from the remote control point, control voltage is applied -to telephone lline 75, as willv be described in subsequent paragraphs, in such manner that the control voltage appears across the lower half of transformer winding 16, as illustrated in` Fig. 3, which then causes energization of relay ||4 only. Closure of contacts |23 of relay |4 eifects ener-l gization of relay H2, thereby disconnecting the output circuitof the monitor receiver from line transformer 16, as described above, and applying' recording mechanism in the speech signals from the line to line-to-grid transformer 95. During direct speech transmission, signals from the recorder-reproducer |0| are prevented from modulating the transmitter by closure of contacts ||9 of relay H4, which effects grounding of control grid 9|, of mixer tube 94. Contacts i8 of relay H4, which are opened with energization of relay |4, remove the ground connection from control grid 92 of mixer 94, thereby permitting impression of signals from transformer 95 on grid 92 of mixer tube 94, and causing modulation of the transmitter.

The system covered by the schematic circuit diagram in Fig. 3 therefore renders the same service as that described in Fig. 2 except for the fact that the circuit indicated is for use on a single carrier frequency instead of multiple frequencies.

In Fig. 4 there is shown a schematic circuit diagram of a. remote control unit designed to operate with the transmitter until indicated in Fig. 3. In this circuit diagram the line transformer |25 couples to the telephone line 15 which connects -to the trailc zone transmitter. The

this arrangement the above-mentioned amplifier and loudspeaker combination is in a position to continually monitor the transmissions from the transmitter, except when the operator desires to make a new recording on the recorder-reproducer, transmit information directly, or effect a retransmission of a signal from a primary radio transmitter within the trac Zone.

The input jack |33 or other suitable switching means allows the use of a desk microphone |34 or a phonograph reproducer |35 in connection with a speech amplier tube |36, as shown. The speech vampliiier yconsists of a high-gain input stage |36 coupled to a triode output stage |31. The gain control |38 allows proper adjustment of the output of this amplier, and the decibel meter |40 indicates the proper adjustment of the gain control '|38 for a given optimum signal level on telephone line 15, to which output transformer IS'EA is connected when relay E27 is closed as will be explained in subsequent paragraphs.

A radio receiver |39, connected to antenna |44 and having a suitable output circuit, may be coupled to speech amplifier tube I3? through input jack I4 A carrier-operated relay |47, connected lto the radio receiver, may be used as will be described hereinafter to control the operation of the system when it is desired to effect automatic. retransmission of a radio signal picked up by the receiver |39.

The power supply for the amplifiers in which tubes |9| and |31 are parts thereof consists of a power transformer |45 which supplies heater current to the amplifier tubes and plate voltage. The full-wave rectier tube |46 has associated with it a conventional filter system MSA. A pilot light |48 is used to indicate that the power supply is in operation when a suitable source of power such as H5 volts A. C. is applied to the primary of transforme |45 through fuses |42 and switch |43. v

In order to permit'direct speech transmission from the remote control point through an associated zone transmitter such as is illustrated in Fig. 3, Without employing the recorder-reprov the tape aww? ducer |,0| of Fig. 3,a transmitter control switch |54, Fig. 4, is provided inthe remote control unit. Whe-n this switch is closed, relay |21 is energized, thereby transferring winding |25A of line transformer |25 from the input transformer |28 of amp1lfier|30 to the output transformer |31A olf amplifier |31, 1and transferring a ground connection from the control grid of amplifier tube |31 to the control grid of amplifier tube 3|, in this manner rendering amplifier |3| ineffective andA amplifier |31 effective. Concurrently with the energization of relay |21, switch |54 also effects application of relay-control voltage on telephone line 15 through the lower winding |25B of line transformer tion of transmitter control relay |4,vFig. 3, at the transmitter end of the telephone line andv effectingdirect modulation of the transmitter through mixer tube 94 and modulator 96 as previously explained. During each direct transmission, When relay ||4 is energized, signals from the recorder-reproducer unit are not impressed on thespeechinput tube 90, as has been explained heretofore, while signals from the monitor receiver ||6 are prevented from appearing on telephone line by the energization of relay 2 whose contacts open the circuit connecting the output of receiver ||6 and line transformer 16 as described in prior paragraphs. v

When a recording is to be made on reproducer unit I0 Fig. 3, from trol point, momentary contact' switch recorder-v |55, Fig. 4,

Simultaneously with the above-described timingoperatiOn, as cam |55 closes contacts |51,

|30 to the output transformer |31A of speech amplifier tube |31. The closure of contacts on the switch |52 causes a relay control voltage to be applied in series with the upper'line winding of line transformer |25, `and the correspond- ,j

ing winding of line transformer 16, Fig. 3, thereby energizing relay Fig. 3, and initiating the operation oftiming motor |20 (Fig.w3) and the recording cycle of recorder-reproducer I6 Fig. 3. The shape of the cam |55' and spacing of contacts |50 are such lthat they allow the contacts |50 to open before the motor control cam |26, Fig. 3, has made a complete rotation, thereby removing relay energizing voltage from relay to prevent re-occurrence of the recording cycle and pre-i' venting any overlap in the recordings made on |02. A recording time indicator |58 (Fig. 4) is also attached to the drive shaft |5|A so that the opy |25, thereby causingenergiza-` ated during effective reception of kcarrier-wave quency is used in `in-Fig. 4, thereby terminating the operation of f equipment of Fig.

energy by radio receiver |41. As shown in Fig. 4, closure of the contacts of relay |41 effects energization o-f relay |21 and applies relay-control voltage to the lower winding |25B of line transformer |25, thus causing retransmission of the received signals by the zone transmitter in the manner previously described. In this manner, signalsmay -be transmitted at relatively high level tojmobile units in a given traic zone along a lane of traffic by retransmission of the original signals by a zone transmitter disposed adjacent )the traffic lane. If, as has been described in preceding paragraphs, a, designated zone fre` l the traffic communications zone, orV an intermediate frequency isemployed, the signals emitted by the zone transmitter or transmitters will break into the lmobile receiver withoutl manual tuning adjustment as the vehicle passes through the localized signaling zone even though signals directly fro-m the originating station may beof different frequency or of such low signal intensity as to render them` rto ywhich the receiver 30 is responsive, andV the signals will be retransmitted at the same freq- .uency- Fl by lzone transmitter I6, to which zone receiver 30 is relatively unresponsive by virtue of the location of antenna 3 l at a point outside the effective signaling eld of zone transmitter |6.

Further discrimination between signal sources, such asr transmitter 34 or transmitter I6, with their associated signal emitting means, may be accomplished by use of a loop or other directionally selective'antenna in connection with receiver 30.` In this instance, the loop or other directional antenna is positioned such that carrier signals from voriginating transmitter 34 are favored and signals 'from zone transmitter |6 are discriminated against, thereby facilitating operation of both transmitters ,on a common carrier frequency without mutual interference between the two signals. n

- Fig. 5 illustrates one type of vremote control as illustrated schematically, in part, in Fig. 4 tojbe employed with systems such as described in the above paragraphs and illustrations of Figs. 1 4, inclusive. Included on the remote control 5 is a line-level meter |6'I, such as a conventional DB meter, and a recording vtirne indicator |62, as is also. illustrated by |58, Fig. 4. A push-to-record'switch |66, Fig. 5,

1 1 schematically illustrated by |56, Fig. 4, is provided as shown.

A loudspeaker, such as |32, Fig. 4, is placed behind the louvers |68, for use in conjunction with a line amplifier such as I3I, Fig. 4, which is incorporated in the control unit of Fig. 5, and allows reproduction of signals from the monitor receivers located at the zone transmitting point. The indicator lights |59 and |10 indicate power-on and voice on operation respectively, the latter corresponding to symbols |48 and |59 of Fig. 4, respectively. A selector dial |60 may be used to actuate a remotely-controlled selective switching mechanism 48, Fig. 2, or automatic selector switch 68, Fig. 2 of any well-known type, making it possible (1) to monitor each traiic zone receiver separately so that individual transmissions from diiferent transmitters in a selected zone can be checked at all times, (2) to permit direct transmission from a zone transmitter 55, Fig. 2, or to effect (3) combined recording and transmitting by means of a recorder-reproducer 5|, Fig. 2, or IBI, Fig. 3, and associated transmitting equipment, such as 55, Fig, 2, as previously explained. A toggle switch ll, Fig. 5, may be used to select either tone dialing or D. C. dialing in connection with the operation of a selector dial IED, in any well-known dialing circuit. The power circuit, voice input, and line circuit terminals may be connected to the rear of the control unit as is customary practice. k

Through the use of a system such as described in the preceding paragraphs, an operator at a central station may. by use of a remote control unit such as described in connection with Figs. 4 and 5, over a single telephone circuit connecting the remote control unit with zone transmitting equipment such as is illustrated in Fig. 3, directly transmit intelligence to a mobile unit proceeding through a given highway, railway or other traic signaling Zone. Also, by use vof the recorder-reoroducer unit IUI, Fig. 3, and associated recording control circuit of Fig. 4. the operator may. by means of relatively short employment of a telephone line, record intelligence at a wayside transmitting point while concurrently transmitting such intelligence to given vehicles in the traic signaling zone. then eiect monitoringq of subsequent transmissions while the recorderreproducer MI is in the normal reproducing position, so that the transmitted intelligence, which is repetitively transmitted to vehicles as they enter the signaling zone. may be checked at the control point. At the conclusion of a given recording and che-cking interval. such` as a threeminute period, during which the telephone line connection is maintained, the telephone line circuit may be terminated. yet the zone transmitter will continue indenitely to repeat the transmission of the recorded intelligence to all vehicles proceeding through the zone. In this manner, telephone calls or other intelligence addressed to trucks. buses, taxicabs. private passenger cars, railway trains. or other mobile units may be picked up by the vehicles upon their entry into the traliic communications zone without need to constantly tie up a telephone facility.

Further, through the use of such zone transmitting equipment placed at strategic points along highways or other lanes of traflic, and by the use of a remote control unit such as described in connection with Figs. 4 and 5', the operator may, by using different telephone circuits extending between the remote control point and the diiierent zone transmitters, place a call for mobile units in any desired traine signaling zone. A call placed for a given truck proceeding on a certain highway may be transmitted in the communications zone along this highway near the point where the highway enters a given municipality. Thus, a recurrent message addressed to a given truck may ask the driver to call the control station fo-r routing information relative to unscheduled pick-ups or deliveries in the city that the truck is entering, or the message may give all the necessary information and ask the driver to acknowledge its receipt by telephone, or by twoway radio if the truck is radio equipped, as soon as the lmessage is received. The same procedure may be followed in paging drivers of taxicabs, buses, or private cars, particularly those driven by doctors and others who regularly employ their cars in their work. It is pointed out that in the event such a mobile unit is equipped with radio transmitting facilities, one of the wayside receivers, such as Si, Fig. 2, which may be tuned to a frequency employed by mobile transmitters may be used in picking up carrier signals from the mobile transmitter and impressing the received signals on the telephone line such as 45, Fig. 2, for transmission to the central control point where the remote control unit, such as 4|, Fig. 2, is installed. In this arrangement of equipment, the output circuit of the wayside receiver -BI may be connected to the telephone line in any wellknown manner, or as shown in Fig. 3, where the output circuit of wayside receiver i It is normally connected with the telephone line 'I5 except during recording control or direct speech transmission periods.

It may also be pointed out that signals from a particular wayside receiver such as SI, Fig. 2, may be applied selectively to the telephone line 46 through an automatic selector switch 68 of any well-known type, or by means of any suitable selecting switching mechanism, such as C18, Fig. 2, in which event the automatic selector switch 6B would not be required.

Fig. 6 represents a modification of the trafc communications system previously described, and is of particular value in eiecting retransmission of radio signals along extended traffic lanes in zones where radio signals initially emitted from a given transmitter require repeating or retransmission. This modication of the system previously described includes an originating transmitter H4 with a microphone |75 and an antenna I'I which may be located at a designated control point along a traffic lane H8 or at other suitable location. The traiiic lane |13 is indicated passing through a tunnel |80, where normal space radio wave energy from a space radio transmitter such as |74 becomes ineective.

To continue the radio service through the tunnel which may be effected on the same carrier frequency, such as FI, originating at transmitter |74, or at a designated. zone frequency, such as F2, which may be an intermediate frequency commonly employed in mobile receivers, or other suitable frequency, a receiver |33, responsive to FI, With a suitable antenna |84, is provided near the tunnel approach. rlhe antenna |84 associated with zone receiver I 83 is disposed in such manner that it is effective in receiving carrier wave energy of frequency FI from originating transmitter Ile, rendering the receiver I 83 responsive thereto. In the event that the retransmission of the signals received from originating transmitter |14 is effected on the same frequency, F i, by means of zone transmitter |83 and trans- Y |39 connects by a plug |41, when the along the line. y ployed'for the purpose of local transmissions at Vzone repeater point.

ineffective, a zone receiver pick-up means |93,

transmitter gnomi? 13 mission line |90, the receiving antenna |04 may be disposed outside of the eiiective localized induction signaling field surrounding transmission line |90 and zone transmitter |38, thereby rendering the receiver |33 responsive to carrier wave energy of frequency FI from transmitter |14 and relatively unresponsive to carrier wave energy of frequency F| from zone transmitter |88. In this manner, mutual interference between signals from originating and repeating transmitters is avoided even though a common frequency is used. Receiver |83 may be provided with a carrieroperated relay circuit |85, as shown by |41, Fig. 4, and an audio circuit |86 for applying received signals to an input circuit of the zone transmitter |88, as illustrated in further detail in Fig. 4, where the audio output circuit of the receiver and jack, |4|A and |40, respectively, to speech ampliiier tube |31. It will be noted that contacts of carrier-operated relay relayis energized, shunt switch |54 and thereby apply relay-energizing voltage to telephone line 15, Fig. 4, and transmitter control relay ||4, Fig. 3, thus automatically vplacing the secondary, or zone transmitter, such as |88, Fig. 6, in operation when a carrier signal is received from the primary transmitter |14.` The output circuit of the zone transmitter v|88 is coupled to an R. F. transmission line |90 which runs along the entire length of .the tunnel and terminates in the terminating unit |9|, said terminating unit preventing standing waves on the transmission line |90 and thereby effecting relatively uniform distribution of signal energy The local microphone |92 is emthe zone transmitter lll, while the local loudspeaker 295 is used for listening purposes at the In order to extend the radio system at the opposite end of the tunnel, where the termination unit |9| is located, and where signals from transmitters |14 and |88 may be |94 at this point is provided with a receiving antenna or other signal said antenna being located in the effective signaling eld of the transmission 'line |90, for the purpose of receiving signals emanating from the zone transmitter |88.

' The zone receiver |94 operated relay circuit |95, similar to that of receiver |83, and an audio output circuit |96, also similar to that of receiver |83 for automatically energizing and modulating its associated zone transmitter |98. A microphone |99 is also provided for local transmissions at the zone transmitter |98. An antenna is connected to the output of the zone transmitter |98 to effect radiation of signal energy within the service area associated with this transmitter.

Thus, a signal from the originating transmitter |14 covers its primary service area and by means of the receiver |83, equipped with a carrier-operated relay, and having the audio output circuit of receiver n |88, the original signal is relayed automatically along the service area of the tunnel |80, designated as tunnel A, as long as carrier signals are emitted by transmitter |14. The signal is then received by the zone receiver |94, which also is provided with a carrier-operated relay and audio means for energizing and modulating the zone transmitter |98, where the original signal is retransmitted throughout the service area of transmitter |98, thereby resulting in effectively covering an extended service area along (Fig. 6) has a carrier#- xit |83 coupled to the zone a trailc ylane without cessation in service either by the shielding effect of tunnel A by the shielding effect of a mountain through which the tunnel passes and which may produce an ineffective signal in the zone (designated as the service area ol? zone transmitter No. 2) on the opposite side of the mountain from that in which the originating transmitter |14 is located.

' A second tunnel 202, designated as tunnel B, may alsor be equipped in a manner identical to that of tunnel A and thereby provide a similar extended service for the system on other traic lanes running through the second tunnel, in the manner described in preceding paragraphs reierring to the illustrative system of tunnel |80.

It is pointed out that the R. F. transmission line |90, Fig. 6, as Well as the corresponding line irl-other figures, need not be aspecial wire or wires installed for the herein described communications purposes. Where roadside wires such as power lines, telephone, and telegraph circuits, or other suitable metallic conductors are present and may be employed in connection with the system of the invention these may be utilized as signal carriers in establishing an induction signaling iield for communications purposes, or in conveying carrier signals along lanes of traffic to strategically-located zone receivers such as |94, Fig.- 6. and associated zone transmitters, such as |98, Fig. 6. In this manner, relatively low-power inexpensive wayside or mobile transmitting and receiving equipment may be used in effecting trafliclane communications over much greater distances than normally would be the case if a conventional radio communications system were to be utilized.

It will be recognized that the illustrative systems described herein are capable of considerable modification and rearrangement without departing from-the spirit and scope of the invention, and it is therefore to be understood that the following claims embrace all such modifications and equivalent arrangements as may fairly be construed to fall within the scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

1. In an inductive communications system for establishing communications within a predetermined signaling area, a transmitter, a signal conducting means connected to the output of the transmitter for establishing a substantially predetermined signaling area, said signal conducting means being disposed substantially parallel to Y'the desired longitudinal extent of said substanducting means, a remote control apparatus hav- -ing means for modulating and monitoring the transmitter and receiver respectively,'and a selec- Vtive switching mechanism connected between the remote control apparatus and said transmitter and receiver for connecting either the transmitter Vor the receiver to the remote control apparatus,

to the end that the remote control apparatus may be connected to the transmitter for modulating said transmitter or to the receiver for vmonitoring transmissions in said. predetermined signaling area.Y

2. In an inductive communications system for establishing communications withinV a predetermined signaling area, a transmitter, a signal conductingmeans connected to the output of the transmitter for establishing a substantially prodetermined signaling area, a termination unit connected to one end of said signal conducting means to restrict the formation of standing waves thereon, said signal conducting means being disposed substantially parallel to the desired longitudinal extent of said substantially predetermined signaling area, a receiver, means connected to the input of the receiver and disposed within the eiTective signaling area for receiving signals impressed upon the signal conducting means, a remote control apparatus having means for modulating and monitoring the transmitter and receiver respectively, and a selective switching mechanism connected between the remote control apparatus and said transmitter and receiver for connecting either the transmitter or the receiver to the remote control apparatus.

3. In an inductive communications system for establishing communications within a predetermined signaling area, a transmitter, a signal conducting means connected to the output of the transmitter for establishing a substantially predetermined signaiing area, said signal conducting Y means being disposed substantially parallel to the desired longitudinal extent of said substantially predetermined signaling area, a receiver, means connected to the input of the receiver and dispo-sed within the effective signaling area for receiving signals impressed upon the signal conducting means, a remote control apparatus having inea-ns lfor modulating and monitoring the transmitter and receiver respectively, a selective switching mechanism connected between the remote control apparatus and said transmitter and receiver for connecting either the transmitter or the receiver to the remote control apparatus and a recorder-reproducer device connectable to the transmitter from the remote control apparatus for recording and reproducing the intelligence impressed upon said modulating means.

4. In an inductive communications system for Aestablishing communications within a restricted area, a transmitter, a signal conducting means connected to the output of the transmitter for establishing a substantially predetermined signaling area, said signal conducting means being disposed substantially parallel to the desired longitudinal extent of said substantially predetermined signaling area, a receiver, means connected to the input of the receiver and disposed within the effective signaling area for receiving signals impressed upon the signal conducting means of the transmitter, remote control apparatus having means for modulating and monitoring the transmitter and receiver respectively, a selective switching mechanism connected between the re- -mote control apparatus and said transmitter and receiver` for connecting either the transmitter or the receiver to the remote control means, a recorder-reproducer device connectaole to the transmitter from the remote control apparatus for recording and reproducing the signals impressed upon said modulating means, and timing means associated with said recorder-reproducer device for establishing a recording cycle of predetermined duration.

5. In a carrier-wave communications system, a plurality of transmitters, a signal conducting means extending for the length'of a predetermined signaling zone, a coupling unit for connecting the output of said transmitters to said signal conducting means, a plurality of receivers having means connected to the input thereof for receiving the signals impressed upon the signal conducting means, a remote control unit having means for modulating and monitoring said transmitters and receivers respectively, and a selective switching mechanism controllable from the remote control unit for connecting said remote control unit with said transmitters for simultaneously modulating same, said selective switching mechanism also lbeing controllable from said remote control unit for selectively connecting independently any one of said plurality of receivers with said remote control unit for monitoring the signal output of each of said receivers.

In a carrier wave communications system, a plurality of transmitters, a signal emanating means, a coupling unit for connecting the output circuit of said transmitters to said signal emanating means, a plurality of receivers having means connected to the input thereof for receiving the signals impressed upon the signal emanating means of the transmitter, a remote control unit having means for modulating and monitoring said transmitters and receivers respectively, and a selective switching mechanism controllable from the remote control unit for connecting said remote control unit with all of said transmitters simultaneously and any one of said plurality of receivers independently.

'7. In a communications system having a plurality of transmitters, a signal emanating means, a coupling unit for coupling the output of said ransmitters to said signal emanating means, a plurality oi receivers having means connected to the input thereof for receiving the signals impressed upon the signal emanating means of the transmitter, a remote control unit having at least one signal source for modulating said transmitters and at least one monitoring means for individually monitoring said receivers, and a selective switching mechanism controllable from the remote control unit for selectively connecting said remote control unit with said transmitters or receivers.

S. In an inductive communications system, a plurality of transmitters each tuned to a diierent frequency, at least one of said frequencies being substantially equivalent to an intermediate frequency employed in the superheterodyne type of radio receiver, a signal emanating means connected to the output of said transmitters, said signal emanating means being disposed for establishing a substantially limited signaling zone, a plurality of receivers each pretuned to respond to one frequency of the various transmitters, signal pickup means connected to the input circuits of said receivers and disposed within the eiective signaling Zone for receiving signals transmitted within said zone, a remote control means, modulating and monitoring means connected to said remote control means, and a selective switching mechanism for connecting said remote control means to either said transmitters or to said receivers.

9. In an inductive communications system, a plurality of transmitters each tuned to a diierent frequency, at least one of said frequencies being substantially equivalent to an intermediate frequency employed in the superheterodyne type of radio receiver, a signal conducting means connected to the output of said transmitters, a plurality of receivers, each receiver being tuned to respond to signal energy of a different frequency, signal pick-up means associated with said conducting means for impressing signal energy upon the input of the various receivers, a remote control means, modulating and monitoring means connected Vto said remote control means, and a 17 selective switching mechanism for connecting said remote control meansto said various transmitters or to said receivers.

l0. In an inductive communications system, a plurality of transmitters each tuned to a different frequency, at least one of said frequencies being substantially equivalent to an intermediate Vfrequency employed in the superheterodyne type of `radio receiver, signal emanating means connectmeans, and a selective switching mechanism for connecting said remote control means With said transmitters and receivers.

ll. In a communications system, a carrierwave transmitter, signal' emanating means connected to said transmitter for establishing a signaling Zone within a substantiallyk predetermined area, a receiver, means connected to the input of the receiver and disposed within the signaling zone for receiving carrier-wave signals from said transmitter, remote control apparatus having means for modulating and monitoring the transmitter and receiver respectively, a selective switching mechanism connected between the remote control apparatus and said transmitter and receiver for connecting either the transmitter or the receiver to the remote control apparatus, a recorder-reproducer device connectable to the transmitter from the remote control apparatus for lrecording the signals impressed upon said modulating means during a recording cycle, timing means associated with said recorder-reproducer device for establishing a recording cycle of predetermined duration, and a second switching means for connecting said recorder-reproducer to the modulating means whereby signals impressed on said recorder-reproducer during the recording cycle are emitted byv said transmitter after completion of said recording cycle.

12. In acommunications system, a' primary radio transmitter operable on a 'predetermined` carrier frequency F1 and having a carrier-wave radiating means for establishing effective radio signaling within a given servicearea, a secondary carrier-wave transmitter also operable substantially on carrier frequency Fl and disposed adjacent a secondary signaling area wherein an effective carrier signal from the primary radio transmitter cannot be received, said secondary carrierwave transmitter the output circuit thereof for establishing a limited-range' signaling within said secondary service area, a radio receiver tunable to carrier frequency F1 emitted by said primary radio transmitter and having an antenna disposed to sive to radio wave energy from said primary radio transmitter but not said secondary transmitter, electric circuit means connected between the output circuit of said receiver and the input circuit of said ,secondary transmitter whereby received signal energy from primary transmitter maybe applied to the input circuit of saidsecondary transmitter withhaving means associated with 1 field effective principally` render said receiver. respon-v to carrier wave energy from' 18 out the existence of mutual interference between carrier Wave signals from said primary andsaid secondary transmitters operating substantially on a common frequency, y

13. In a communications system, a carrierwave transmitter, signal emanating means connectedto the output of said transmitter for establishing a signaling eld within a substantially predetermined signaling area, a carrier-wave receiver disposed adjacent said transmitter and responsive to carrier wave` energy from said transmitter, a signal recording and reproducing means disposed adjacent said transmitter and said receiver, electrical circut means normally connecting a signal output circuit of said recording and reproducing means to the input of said transmitter whereby recorded intelligence is normally emitted by said transmitter, a telephone line, a remote control unit connected to said telephone line, a relay normally connecting said telephone line to an output circuit of said receiver when said relay is de-energized and operable tov connect said telephone line to an input circuit of said signal recording and reproducing means when said relay is energized, said remote control unit having a signalV transducer and signal source for signal reproducing and recording functions respectively,

14. In a communications system, a primary carrier-wave transmitter operable on a predetermined carrier frequency FI and having a carrier-wave radiating means for establishing effective signaling within a given signaling area, a secondary carrier-wavetransmitter also operable substantially on carrier frequency Fl and disposed adjacent a secondary signaling zone'wherein an effective -signal from the primary transmitter cannot be received, said secondary transmitter having means associated with an output circuitA thereof for establishing a limited-range signaling field effective principally within said secondary signaling zone, a radio receiver tunable to carrier frequency Fl emitted jby said primary transmitter and having signal pick-up means forV rendering said receiver responsive to carrier wave energy from said primary said secondary transmitter, electriccircuit means connected between the output circuit ofsaid receiver and the input circuit of said secondary transmitter whereby received signal energy from said primary transmitter may be applied to the inputfcircuit of said secondary transmitter without the existence of mutual interference between carrier wave signals from said primary and rsecondary transmitters operating substantially on a common frequency.

15. In a communications system, a primary radio transmitter operable on a predetermined carrier frequency FI and having a carrier-wave radiating means for establishing effective radio signaling within a given service area, a secondary carrier-wave transmitter also operable substantially on carrier frequency FI and disposed adjacent a secondary' signaling area wherein an* Ytransmitter,` said antenna also, being disposed to*- transmitter but not tov 19 render said receiver unresponsive to carrier wave energy from said secondary transmitter, electric circuit means connected between the output circuit of said receiver and the input circuit of said secondary transmitter whereby received signal energy from said primary transmitter may be applied to a signal input circuit of said secondaryv transmitter without the existence of mutual interference between carrier wave signals from said primary and secondary transmitters operating substantially on a common frequency, and a carrier-operated relay connected to an output circuit of said receiver, said relay having contacts electrically connected to apply electric power to said secondary transmitter when said relay is energized during reception of a carrier signal and to remove power from said secondary transmitter when said relay is de-energized by lack of a received carrier signal from said primary transmitter.

16. In a communications system for relaying communications into and out of an area which is ordinarily not serviceable by a space radio transmitter including, a space radio transmitter having an antenna for radiating radio wave energy effective in a primary service area, a secondary carrier transmitter, signal emanating means connected to the output of said secondary carrier transmitter and being disposed substantially within the area to be embraced by the effective signaling eld of said secondary carrier transmitter, a zone radio receiver having antenna means disposed for reception of signals from said space radio transmitter, the signal output circuit cf said receiver being connected to the signal input circuit of said secondary transmitter for modulating said secondary transmitter by signal energy received by said radio receiver, relay means connected intermediate said receiver and said secondary transmitter for activating said secondary transmitter when signals are received through said receiver from said space radio transmitter, a second zone receiver, signal pick-up means disposed within the effective signaling field of said secondary transmitter and having one end thereof connected to the input circuit of said second Zone receiver, a second space radio transmitter having an input circuit thereof connected to the output circuit of said second zone receiver, relay means connected intermediate said second zone receiver and said second space transmitter for activating said second space transmitter when signals are impressed upon said second zone receiver, and signal emanating means connected to the output of said second space transmitter for transmitting the signals imn pressed upon the second zone receiver.

1'7. In a communications system for relaying communications into and out of an area which is ordinarily not serviceable by a space radio transmitter including, a space radio transmitter having an antenna for eifecting radiation of radio wave energy within a primary service area, a secondary transmitter, a termination unit, signal emanating means having one end thereof connected tc the output of said secondary transmitter and the other end thereof being connected to said termination unit whereby formation of standing wave energy is inhibited, said signal emanating means being disposed substantially within the area tc be embraced by the effective signaling field of said secondary transmitter, a first zone radio receiver having antenna means disposed for reception of radio signals from said space radio transmitter, the signal output circuit of said receiver braced by the effective being connected to a signal input circuit of said secondary transmitter for modulating said secondary transmitter by received signals impressed on the input thereof, relay means connected intermediate said receiver and said secondary transmitter for activating the said secondary transmitter when signals are received by said receiver from said primary transmitter, a second zone receiver, signal pick-up means disposed within the eifective signaling range of said secondary transmitter and having one end thereof connected to the input of said second zone receiver, a second space radio transmitter having an input circuit thereof connected to an output circuit of said second zone receiver, relay means connected intermediate said second zone receiver and said second space transmitter for activating said second space transmitter when signals are impressed upon the second Zone receiver, and signal emanating means connected to an output circuit of said second space transmitter for transmitting the signals impressed upon the second zone receiver.

18. A communications system for relaying communications into and out of shielded areas which are not ordinarily serviceable by a space radio transmitter, comprising, a space radio transmitter having an antenna for effecting radiation of radio wave energy within a primary service area, a plurality of secondary transmitters for serving said shielded areas where radio wave energy from said space radio transmitter is ineffective, a plurality of radio receivers for receiving the signals originating in the space radio transmitter, each of said receivers being ccnnectable to one of said secondary transmitters, relay means connected intermediate each of said secn ondary transmitters and its complemental receiver for activating said transmitter when carrier wave signals originating in the space radio transmitter are received1 and signal emanating means connected to the output of each of said secondary transmitters and being disposed substantially within the shielded areas to be emsignal range of each of said secondary transmitters.

19. A communications system for relaying communications into and out of metallically shielded areas which are not ordinarily serviceable by a space radio transmitter comprising, a space radio transmitter having a range for embracing at least a primary service area, a plurality of secondary radio transmitters, a plurality of radio receivers for receiving the signals of the space radio transmitter, one of said receivers being connectable to each of said secondary radio transmitters, relay means connected intermediate each of said secondary transmitters and its complemental receiver for activating said transmitter when signals are received by the receiver from the space radio transmitter, signal emanating means connected to the output of each of said secondary radio transmitters and being disposed substantially within the metallic shielded areas to be embraced by the effective signal range of each of said secondary radio transmitters, and a radio receiver having antenna means disposed for reception of signals from at least one of said plurality of secondary radio transmitters.

20. In an inductive communications system, a transmitter tuned to an intermediate frequency employed in the superheterodyne type of radio receiver, signal emanating means connected to the output of said transmitter, said signal emanating means being disposed for establishing a substantially limited signaling zone, a receiver pretuned to respond to the frequency of said transmitter, signal pickup means connected to the input circuit of said receiver and disposed Within the effective signaling area for receiving signals transmitted Within said zone, remote control means, modulating and monitoring .means connected to said remote control means, and selective switching mechanism for connecting said remote control means to either said transmitter or to said receiver.

21. In an inductive communications system, a transmitter tuned to an intermediate frequency employed in the superheterodyne type of radio receiver, signal conducting means connected to the output of s aid transmitter, a receiver being tunable to respond to signal energy from saidl transmitter, signal pick-up means associated with said conducting means for impressing signal energy upon the input of said receiver, remote control means, modulating and monitoring means connected to said remote control means,

and selective switching mechanism for connecting said remote control means to said transmitter or to said receiver.

22. In; an inductive communications system, a transmitter tuned to the intermediate frequency employed in the superhetercdyne type of radio receiver, signal emanating means connected to the output oi said transmitter, said signal emanating means being disposed 'along a lane of traiiic for establishing a substantially predetermined longitudinal signaling zone, a receiver pretuned to respond only to the frequency of the transmitter, signal pick-up means disposed within the effective signaling zone for receiving said transmitted signal and being connected to the receiver, remote control means, modulating and monitoring means connected to said remote control means, and a selective switching mechanism for connecting said remote control means With said transmitter or receiver.

WILLIAM s. HALSTEAD.