US2479701A - Transmitting system - Google Patents

Description

Aug. 23, 1949.

Filed Feb. '7, 1944 T. l. RESS TRANSMITTING SYSTEM '6 Sheets-Sheet l Ma/L E TfLE, 575/7704/ INVENTOR. WMM/yf Fes;

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2 EN@ 500A ad* 300X 5% l! 'INVENTOR 750A/M5 Hss Patented Aug. 23, 1949 ity of. :tiqunkng channels; to 'theLio'rrfatuch stations of automaticmean-S 'for testing-and @electing =id1e .cnannals Qyer which,.zwmmmiwtiohimaybew- .tablishgd withthenntlal station oraexQha-ngapato 2General1=descnipti0n generar-the"completion of Lcpnnectins `over "the novel system involves l the .Gallina "bif? 'the ness by tuning the substation transmitter and receiver progressively over the frequency range of the system. A special signal or tone is placed upon idle channels at the central exchange, and the substation apparatus will automatically remain tuned to the first idle channel frequency encountered and marked by such tone in the aforesaid testing operation.

When an idle channel is seized by the substation, the identifying designation of the calling station is thereupon automatically transcupied trunking channel is blocked for the dura'- tion of the call.

Referring to the block diagram of Fig. 1, there is provided at the central or link station a wideband ultra high frequency radio transmitter A adapted to transmit over a band preferably 1.5 megacycles wide, together with ultra high frequency receiving means B adapted to receive over a band of greater width than the transmitting band, the transmitter operating on frequencies from 100 to 101.5 megacycles and the receiver operating on frequencies from 80 to 82 megacycles, in the present embodiment.

Channel converter means, generally indicated at C, is utilized to provide at least one call channel D, operating in this instance on 500 kilocycles for transmitting call signals from a calling device E located at a central control or switchboard F. In addition to the call channel or channels (several may be required), there are provided a number of talking or trunk channels numbered consecutively from I to |00, and each separated by a band width of 10 kilocycles, preferably.

The wide-band receiver B is connected to a plurality of channel separators, generally indicated at G, and numbered consecutively from l to and each separated in frequency from the other by intervals of 20 kilocycles.

Drop connections from each of the channel converters and separators are brought out at the switchboard F in jacks H, also numbered from I to 100, to correspond to the talking channels, so that the operators telephone set may be plugged into any of the 100 talking channels for two-way communication thereover.

At the right-hand side of Fig. 1 are shown the instrumentalities of one substation, which include an ultra high frequency wide-band receiver J operating on a band width of 1.5 megacycles, that is, from 100 to 101.5 mc., and a U. H. F. transmitter K operating on a band 2 megacycles wide, that is, from 80 to 82 mc.

The substation receiver is tuned by a channel tuner L, actuated automatically by a channel tuning motor M, which simultaneously actuates a channel tuning converter N for tuning the transmitter K to any of the trunking frequencies included within the principal link carrier frequency. The automatic tuning means is so arranged that when the channel tuning motor M is set into operation, the substation transmitter and receiver will be tuned simultaneously over their respective trunking channelV frequency bands for two-way communication with the central station unit over the idle channels selected thereby.

4 The substation receiver is normally kept tuned (with the channel tuning motor means at a starting position) to one of the call channels D of the central station, and when a certain sequence 5 of call code signals of pre-arranged frequency is received thereby, a call selecting device P sets the channel tuning motor means M into operation, so that the substation transmitter and receiver will automatically begin to tune over the range of the aforesaid operating band, testing for an idle trunking or talking channel.

Means is provided for rendering idle channels selectively distinguishable from busy channels, the preferred form of such means being the transmission of a characteristic idle tone over the various idle channels, such that when the substation receiver is automatically tuned, as aforesaid, over its operating band and the first idleV tone is received, the call selector will be actuated at once to stop the automatic tuning means or channel tuning motor M, so that the substation will be conditioned to operate on the particular frequency of such idle channel.

Upon automatic selection of an idle channel by the called station, the transmitter K thereat is operated to radiate a carrier wave and an automatic station identification device S, cooperating with the transmitter modulator T, will cause the call number of that subscriber to be transmitted over said carrier to the central exchange or link station operator. The reception of this carrier at the central station causes a relay in the corresponding channel separator circuit to operate and turn on a busy or line lamp located over the corresponding channel jack on the switch board. The attention of the operator is thus called to the answering channel and by connecting the operators telephone set to this channel, the answering subscriber can be identified. Upon completing the connection, a go ahead signal is transmitted from the central station to the mobile station. rIhe reception of the go-ahead signal at the mobile station operates a local signal or buzzer thereat to announce the call to the subscriber.

Should the subscriberqwish to place a call, in the diagrammatic arrangement of Fig. 1, he removes his hand-set in the usual manner, setting the automatic call selector device P into operation, and thereby causes the aforesaid channel testing operation to go forward until an idle channel is found, whereupon the station identification device S causes the call number of this particular substation to be transmitted to the central station, with a resultant illumination of a signal lamp over the jack terminal of the calling channel at the central switchboard; when the operator answers, the subscriber passes the desired number, and the operator completes the call Vin themanner heretofore described.

Detailed description At the top of Figs. 2 and 3 (read together) there are shown by block symbols, appropriately designated, the major unit components of a conventional ultra high frequency (U. H. F.) radio transmitter, such apparatus including a crystalcontrolled oscillator doubler unit, a buffer-tripler stage, a frequency tripling stage, an U. H. F. amplifying unit, an U. H. F. driver stage (Fig. 3) the output of which is ampled by an U. H. F. power amplifier unit, which has its output modulated by the unit so-designated, in cooperation with the channel converter system shown in detail to the left thereof in Fig. 2. For'purposes of this specification, it may be cara-7er 5 pointed out here that the individual instrumentalities of the foregoing transmitter components indicated by block units are well understood in the art, so that a detailed description and illustration of these parts is deemedk unnecessary.

The principal apparatus interposed between the central office switchboard and the transmitter therefor, is the channel conversion means, the function of which is the provision of a plurality of sub-frequency carriers or trunking and signalling channels, the term sub-frequency being utilized here to designate the various carrier frequencies which are additively contained within the modulation band of the ultra high frequency (U. H. F.) carrier of the central oiice transmitter.

Since the apparatus and circuit connections for one channel conversionunit differ from those of another unit only in the frequency at which it is capable of operating, only 'one suchr unit need be described in detail. Y

Beginning at the central exchange switchboard I (Fig. 2), conductors II lead from the tip and sleeve terminals I2 of the jack terminal for channel No. 1 to the primary I3 of an input transformer whose secondary winding I3a connects respectively to the control grid I5 of tube I1 and to ground.

The output of the modulator tube I1 is passed through a coupling transformer 2Il connecting with the plate I9 of the modulator stage and at junction 2I with the positive plate power lead` 22. The secondary winding ofy transformer 20 has one terminal connected to plate power lead 22., and its other terminal connected via conductor 23 through the primary winding 24 of a radio frequency injector coupling transformer and thence via conductor 25 to the plate- 26. of a radio frequency amplifier tube 21.

An oscillator tube 28` has its control grid 29 connected to a crystal oscillator unit 30, the plate 3I of this tube being connected to `power lead22 through the primary Winding `32 of a coupling transformer tuned by condenser 33. The secondary winding of this coupling transformer connects at 34 with the ground I E and at 35 to the control f1 grid 36 of the R. F. amplifier tube 21.A

The frequency of the trunking channel carrier afforded by the foregoing converter unit is determined by the crystal control means 30, and the voice frequency energy from the talking circuit is picked up at the jack terminals of the switchboard andlimpressed uponA the trunkingA channel carrier through the modulator stage or tube I1.

The channel carrier, thusv modulated, isV impressed upon the main transmitting carrier through the injector coil secondary winding 24a (Fig. 3), there being aeplurality of such injector coils 24h. etc., corresponding in` number to the number of c all channels and trunlring carrier or sub-,frequency channels used, preferably one hundred, as heretofore stated.

, All the injector coils 24d, 24h, etc., are con-V nected in parallel and feed into a channel mixer 42 via conductor 39, leading to the control grid 40 of the mixer tube, and conductor 39a leading tothe cathode lead 4I of this tube. Mixer tube 42 has its output connected from its plate 38 and second grid 43 condenser-coupled via leads 44' and 45 to a wide-band amplifier 46, which in turn passes its output into. the modulator unit, so-designated for impression upon the main carrier through the U. H. F. amplier unit, and it should be observed here that aside band of this main carrier is cut-oil` by a 'side-bandfllter so designated ahead of the radiating antenna, in

6 order yizo-reduce the' overall `frequency band (which would otherwise be occupied) to nearly one-half.

vFor purposes of illustration, a second channel converter unit is shown in Fig. 2 connected via conductors I Ia to switchboard jack terminals I2a, and this unit has its output coupled through another of the injector coil windings 240 to the channel mixer, such converter unit being identical' to that just described excepting that it is tuned, as by its oscillator crystal control unit 50d, to a frequency about l0 kilocycles away from the frequency of the first-described unit, so as to provide a second voice trunking channel distinct from the others, it being understood that addition converter units of this type are included in the actual installation for the transmitting side of the required one hundred trunking channels.

The same kind of converter means is employed for call channel purposes, one such channel unit being shown onFig. 2 connected from a call signal control unit 8 at the switchboard via conconductors I In: to the input transformer I3y for a call channel modulator tube Ila. The output 'of this call channel converter unit is coupled with the injector coil 2th (Fig. 3). Thus, a call channel carrier of 500 k. c., modulated by special call signals under control of the call coding device 8, as will be more fully explained hereinafter, is impressed upon the control station transmitter through the channel mixer stage 38 and associated instrumentalities, in the same manner as the voice-modulated trunking carriers.

In order to afford two-way communication for each trunking' channel, there are provided, as shown in Fig. 2 (read with Fig. 3), a plurality of channel separators, which are essentially special individual receiving circuits provided with frequencyconv'erter means and certain control relay means, and respectively picking up their input energy from a master frequency converter 48 (Fig. 3), having its output connected via conductors 50 through the parallel primaries of a plurality of injector coils 5Ia, 5Ib, etc.

The master frequency converter receives energy from an U. H. F. receiving antenna 41, which is provided with metal shield means 41a to. reduce the field strength of nearby mobile stations, and this incoming energy Iis passed through an amplifying stage 41h having its output coupled to a mixing and converting stage 48 Via coupling transformer 48a. A crystal-controlled master oscillator 49 (tuned to '19 mc., for example) coupled via transformer 49a with the mixing converter stage 48, and the resultant intermediate frequency, including the mixed trunking carriers, is passed through coupling 49D and conductors 50 to the several injector coils 5Ia, 5Ib, etc., for selective distribution to the several channel converter units.

Considering the converter circuit for channel No. I, for example, the mixed-frequency energy from the main control ofiice master frequency converter is picked up by the winding 5I (Fig. 3) of the corresponding injector coil, amplified by radio frequency amplifier 5I, then coupled to the input of a converter 52 via conductors 53 and 54, the Iinjector coil being tuned by condenser 55 for selective response to the incoming trunking carrier frequency of this particular chann-el.

Converter 52 includes an oscillator circuit including a parallel condenser and inductance 565 and feed-back coil 51, setting up local oscilla--` tions'l which beat with the incoming injector frequency, giving a resultant intermediate 'frequency which Iis passed via windings 59 (Fig. 3) and 60 (Fig. 2) of a coupling transformer and conductors 6I and 62 to the input of an intermediate frequency ampliiier tube 64.

`The output of the intermediate frequency amplifier is passed to coupling coil 66, from which it is transferred in part via tuned winding 61 to plate 68 and cathode 69 of a twin diode detector, and demodulated, this portion of the demodulated energy being coupled via dropV resistor 10, condenser 1|, conductor 12 to the control grid 13 of an audio frequency amplifier, and the amplified voice component is then transferred through output transformer 14 and conductors 15 and 16 to conductors |2x leading to the jack terminals of channel No. I at the switchboard.

Since there is a wide variation in the signal strength from the substations, automatic volume control (A. V. C.) is provided at the central station for each converter unit, such A. V. C. being derived from the drop across resistor 10 in diode circuit 68-69, and acting to vary the grid bias voltage applied to the preceding amplifier tubes 64, 52 and 5|.'c.

A feature of the foregoing channel separator circuit is the idle channel signal control means, which includes (lower Fig. 2) a busy lamp 80 above the corresponding channel jack on the switchboard, one terminal of which lamp connects with power supply line 8|, and the remaining terminal of which connects via conductor 82 to the normally open make contact 83 of the idle channel relay 84. The coil 85 of this relay is in series with plate 86 of the D. C. amplifier tube and the posiitve plate or B power supply line 81.

This idle channel relay 84 is actuated by the second diode unit of the detector, which includes tuned coupling coil 61a connected in a rectifying circuit with plate 60a and cathode 69a of the diode, the D. C. control component from which connects via conductor 88 to control grid 89 of the idle channel relay tube. If channel No. 1 is busy, relay coil 85 is energized through the plate circuit 86-81 by virtue of the control voltage applied to grid 89 from the diode detector circuit 61a, 68a, 69a, 88, causing contact 83 to make with its companion contact 83a and complete circuit to illuminate the busy lamp 80.

A further important function of the idle channel control relay circuit is the application or removal thereby of an idle channel buzz signal from source conductor 90, via conductor 9| and normally closed contacts 92 on the idle channel relay and through coupling condenser 93 to primary winding 14a of the output transformer leading to the channel jack I2. Thus, the idle channel buzz signal is normally applied by closed contacts 92 to the switchboard jack circuit, through transformer 14, and also via conductors to the input side I3 of the corresponding channel converter unit, so that the idle signal is transmitted constantly over this channel so long as it remains idle; but so soon as the channel is seized or busy, relay coil 85 becomes energized to open contacts 92 and disconnect the idle tone, while at the same time closing relay contacts 83-83a to illuminate the busy lamp.

The circuit for additional channel separator units, such as that shown for channel No. 2, is identical to that just described for channel No. 1 excepting, of course, that the tuning components thereof are principally resonated to the partic-l ular frequency of channel No. 2.

Subscriber station equipment Considering nowY Figs. 4 and 5 together, the receiving equipment at the substation consists generally of a. superheterodyne type circuit with a demodulator for the modulation band, and certain automaticA call selector, filter and switching means. Y y

. The broad band carrier with its mixed trunking or sub-frequency carriers is picked up by the antenna |00 (Fig. 4) vand passed through input coupling means |0| to a conventional U. H. F. amplifier stage |02, whose output is transferred via coupling transformer means |03 to the input leads |04, |05 of an U. H. F. frequency converter stage |06, and the output of this stage is passed via .conductor |08 and a tuned coupling unit |0817 to the input side of a rst intermediate frequency amplifier |09, which in turn passes its output to the input of a second intermediate frequency ampliiier |I0 through a tuned coupling unit I |0b.

Y The mixed channeltrunking carriers are next passed viaconductors I I5, I I6 to a diode detector, which delivers the mixed modulated side bands of channel trunking carriers to a special tuning radio frequency converter I I8 through coupling ||1. This converter by beating selectively variable frequencies generated by its own tunable oscillator circuit I|9 with the output of the diode or second detector in coupling circuit I I1, makes possible the selection of a particular one of the trunk carriers, and to this end, coupling circuit ||1 is provided with a variable condenser II1a, which is ganged with a variable condenser ||9a of the converter oscillator circuit for joint tuning by connection with a drive shaft |20 actuated by channel tuning motor |2I through reduction gear means |22.

Any trunking carrier frequency selected by the aforesaid converter means, is demodulated and amplified as to its voice component in a combination detector and amplifier |25 having detector diodes |26 and cathode |21 connected to the converter output via conductors |28, |29, a sharply tuned band filter circuit I 30 being inductively coupled with circuit |29 to the output or plate circuit ||8a of the converter. The rectied component in the diode plate circuit is impressed upon a control grid I3| in tube |25 via a potentiometer |32, thus controlling the amplifier current flow to plate |33, this plate circuit being coupled via transformer |34 and conductor |35 to the telephone receiver of the sub-station hand-set, as will presently be explained.

Automatic volume control is provided for the converter |06 and intermediate frequency amplifiers |09, IIO, by the drop across resistor IIBa in the cathode lead of the diode detector, from which the bias volatage is passed via filter resister lia, conductors |05, |04 to the control grid of the converter, and viaconductors |08a and I I0a, respectively, to the control grids of the two intermediate frequency amplifiers.

The voice frequency output of the detectorampliiier |25 is also impressed, via conductor |40 upon the grid |4| of a buffer stage |42 (Figs. 4 and 5 together) for the purpose of energizing certain call selector means, which includes a plurality of tuned band pass filter circuits generally indcated at |44, and numbered serially from 1 to 5, all in series via conductor |45 with plate voltage Supply lead |46.

Each of the individual call selector filters |44 is connected to one of the contacts numbered serially from l to on a stepping switch generally indicated at |41, and having a movable wiper contact |48 adapted to be rotatively stepped by a ratchet mechanism |49 into engagement with any of said contacts. The stepping switch wiper contact |48 is connected via condenser |50 to the grid |52 of a selector relay tube |53, which has the coils |55a, |552), of a slow and fastrelay in series with its plate |54 and plate voltage supply lead I 45 for control of the stepping ratchet mechanism.

Calling of subscriber stations iseffected by transmission of a series of coded or predetermined call signals at audio frequencies, and the first three of the call lters |44 are each peaked or sharply tuned to one of these frequencies. For example, the lter connected to contact #I may be peaked at 300 cycles, lter #2 at 492 cycles, and lter #3 at 2750. Ten frequency intervals are considered practical for such a call lter system, and will afford possible combination and permutation groupings of frequencies taken three at a time, which will give 1000 call signals each consisting of three consecutive call frequencies.

The subscriber stations are preferably each assigned a call number consisting of digits or groups of digits from 1 to 9 and zero, and to each such call digit (inclusive of zero) is assigned a particular audio frequency for selective signalling purposes. In one arrangement, the digits are assigned the frequencies tabulated hereafter:

Cyc. 1 300 Assuming, by way of example, that the assigned call of a substation were 130,` the operator would set up the digits 1'3-0 on a call coding device (B in Fig. 2) hereinafter more fully reerredr to, and would thereby cause the call channel carrier to be modulated by three successive signals, the iirst of which would be at 300 cycles, the second, at 492 cycles, and the third at 2750 cycles.

If the substation illustrated in Fig. 5, particularly, were intended to respond to such call, filter #i in group |44 would be peaked or tuned to the frequency of the rst call signal or 300 cycle; filter #2 at 492 cycles; and lter #3 at 2750 cycles.

A call signal at 300 cycles would be sufficiently passed through filter section #I to impulse the gridv |52 of the selector relay tube and cause a current ow through the windings of slow and fast relays |5505, 555i), and such energization of the latter relay would effect closure of fast relay contacts |55 to energize the selector switch ratchet magnets |51, causing ratchet pawl |49a to. advance the ratchet and associated contact arm |48 to Contact #2, thus connecting lter #2 in the grid circuit of the selector relay tube |53. y rIfhe next incoming call signal, being at the proper frequency of 492 cycles, will be passed by 'filter #2 to cause another impulsing of the slow and fast relays, so as to effect advance of the selector switch contact arm |48 to contact #3; and the next call signal at 2750 cycles will pass filter #3 to cause a further advance of the selector contact arm |48 to contact #4 in the same manner.

It may be pointed out at this juncture that the function of the slow-acting relay, which is of the slow-to-release Variety, Vis to control the locking of the ratchet mechanism to prevent return of the wiper contact arm |48 to normal or starting position by its spring |49b so long as proper call signal impulses continue to be received and corresponding impulses traverse the plate circuit of relay tube |53. is accomplished by reason of the fact that each call signal impulse which actuates the ratchet relay to advance the selector switch, also eects closure of slow relay contact 59 to energize locking magnet |60 from the main power `source or battery 2|9, via. conductor |58, said contact |59, conductor |6|, resulting in attraction of locking dog |64 to engage the ratchet means |49 so that the latter is held against retrograde movement to starting position by spring |49b.

Since relay |55a is slow to release, it will tend to hold up land lock the ratchet mechanism against return so long as the call signal impulses continue to come in in proper sequence.

However, should an improper call signal traverse the filter means |44|45, the selector relay tube |53 would fail to deliver further impulses to the relays |55a, |5517, and slow relay |55a would release, breaking the circuit to holding magnet |50 at contacts |59, allowing locking or holding dog |64 to be Withdrawn by its spring 64a, so that spring I 49h would restore the selector contact arm |48 to starting position.

When the contact arm I 48 arrives at contact #4, cam |69, among other things, closes contacts |B2a. The purpose of this is to hold up the selector switch at position 4 while the idle channel test goes forward.

Driven jointly with the selector switch wiper |48 by drive shaft |68, is a switch cam |69, which normally rests upon and closes motor control normalizing contacts |10a to energize channel tuning motor 2| through motor control means |15 for operation to normal for starting position, via conductors |10-|12, said motor being reversible, the control means |15 for this motor being described in detail hereinafter in connection with Fig. 6.

When the call selector stepping switch moves to position #4, as by reception of the proper sequence of call signal frequencies, cam |69 closes contacts |13 and energizes the tuning motor in the reverse direction via conductors |10|1| and control means |15, hereinafter explained, and the gang tuning condensers 1a, H941, 203, begin progressive tuning of both the substation receiver and transmitter over the trunking carrier frequency range, as heretofore described. When an idle channel is tuned in (modulated as heretofore explained by the "idle channe buzz signal) which is of a predeter. mined characteristic frequency, for example, 200 cycles, to which vcall lter #4 is tuned, then the selector relay |5512 will be actuated again to cause the stepping .switch to advance to position #5, thus causing cam contacts |13 to open and stop the channel tuning motor |2| with the gang condensers `tuning the receiver and transmitter to the frequency of the idle channel over which the idle channel buzz tone was thus received.

Y l1 At position #5, the stepping switch cam |69 will close contacts |16, causing energization of the station transmitter via conductors |11, actuating power relay |18 to connect power through contacts |18a from the line to the transmitter power pack |19 (Figs. 4and 5), so that the substation transmitter (Fig. 4) conditioned for operation. In addition, cam |69 at position #5 also closes contacts |80 to energize the automatic station identification transmitter motor |82 via conductors |8|. As inrposition 4, contacts |62b lkeep the locking magnet |60 energized and prevent falling back of the selector.

The automatic station identification transmitter shown is of the magnetic tape'type, 'in'which a vmagnetizable wire loop |83, on which is magnetically impressed a vocal A(or other) recording of the identification caller telephone number of this particular station; and this wire loop is driven, by drive wheels 83a and motor |82, through the field of a pick-up coil IBL-which causes the station transmitter to be modulated with the call identification recording via microphone lead |85. Y 'v I VAt this juncture the substation transmitter may be conveniently described'. Aparty from the novel channel tuning means, this transmitter may be of conventional U. H. F. design, including (Fig. 4) a microphone input transformer |86 controlling voice input amplifiers |81, |88, coupled by modulator input transformer |89, to a pair of modulator tubes |90, |9|, whose output is impressed upon the antenna coupling coil |9311 through modulation transformer |92 to modulate the U; H. F. output of the transmitter power amplifier stage |93. The remaining transmitter instrumentalities include an oscillator 94, tuned by a crystal control unit |95, and having its output frequency modified by a frequency multiplier stage |96, the resultant frequency being subject to variation over the range of the trunking carrier frequencies in an U.v H. F. converter stage |91, which controls a driver stage |98 ahead of a power amplifier stage |93.

The transmitter channelv tuning means includes (Fig. 4) a variable oscillator 200 having a plate inductance 20| coupled with a grid inductance 202 tuned by a variable condenser 203 which is 'driven from'the channel tuning motor drive shaft |20, along with receiver condensers 1a, ll9a. The output of this 'channel'tuning oscillator is passed via conductorV 204 to injector grid |91a in the U. H. F. converter stage to produce a selectively variable resultant transmitter frequency corresponding to the several4 trunk carrier frequencies.

Resuming the foregoing description, wherein the call signal step switch had come to rest at position #5, in which the transmitter power pack was energized by relay |18, as described, and the automatic station identification transmitter started, consequent upon the reception of the proper Vincoming call code signals, with the result that the subscribers transmitter would then be radiating at one of the idle trunking carrier frequencies determined by the aforesaid channel testing operation. The reception of this trunking carrier frequency (assume it to be that of channel #D at the control exchange (Fig. 2) causes the D. C. idler channel relay means 84-85 to close contacts 83, 83a, illuminating lamp 80 at the switchboard to show the trunk channel busy, at the same time opening contacts 92 to remove the free or idle channel buzz signal from this channel.

Upon ascertaining the call number of the station answering over this channel by listening to the call emitted by the station identification means |83-I84, to determine if the proper station is answering, the operator interconnects the calling and call stations at the jack terminals and closes a go-ahead signal switch 208 (Fig. 2) connecting a go-ahead tone of distinct frequency, for example, 100 cycles, momentarily to the central station transmitter from tone source line 209 via one of the jack contacts |2y.

The go-ahead tone received at the called substation (Figs. 4 and 5) will be passed by selector lter #5 to contact #5, causing the step switch to advance to position #6 in the manner heretofore described, at which cam |69 will close contacts 2|2 across conductors |11 to hold up the power supply relay |18. Cam |69 will at this sixth position also close contacts |3511, connecting the audio output of the receiver amplifier from line |35 to the station telephone receiver at terminals |3519. Cam |69 at this position will also close contacts 2|5, energizing the station signal or buzzer 2 i8 via conductors 2| 6 and main battery or power source 2 9 through the normally closed telephone set contacts 2|1, which will open to stop the signal 2|8 when the subscriber lifts the set to answer. In addition, contact |62c is closed and keeps locking magnet |60 energized.

Lifting of the telephone set to answer also closes transmitter microphone contacts 220 at the phone set, so that the microphone of the latter is connected with the transmitter at terminals 22|, 222 to conductor |85.

When the telephone hand-set is lifted to answer the call, the cradle plunger 225 (Fig. 5) rocks lever 226 thereby causing arm 221 to move downwardly to rotate wheel 228 in a clockwise direction. During the clockwise rotation of wheel 228 the upper end of arm |a is engaged yby a cam projecting from the face of wheel 228 and is moved thereby towards the shaft |68. When wheel 228 is fully rotated this cam passes beyond the tip of arm |99a permitting it to restore to normal. When the call is finished and the hand-set is restored, wheel 228 is rotated counterclockwise by arm 221. During the return movement of wheel 228 the upper end of arm |90a is again engaged by the cam projecting from the face of wheel 228, but this time arm |90a is moved away from shaft |68 causing contacts |90 to open and release locking magnet |60 so as to permit shaft |68 to be restored by spring |4917. When wheel 228 reaches its normal position the cam projecting therefrom passes beyond the tip of arm |90a permitting it to restore and reclose contacts |90.

Should the call be outgoing from the substation shown in Fig. 5, the subscriber lifts the handset in the usual manner, which sets the selector switch on position #4 through the agency of levers 225, 226, 221 turning wheel 228 so that dog 229, which is engaged in ratchet tooth 23Go, will turn the ratchet 230|) and cam |69 to position #4; causing the channel tuning motor to start the testing operation for an idle channel, which, when located, will by its idle tone, cause the selector switch to be advanced to position #5 in the manner explained, energizing the transmitter and signalling the central exchange operator as heretofore described.

In Fig. 6 are shown details of the motor control unit |15, wherein a common lead |10 from battery 250 is connected (in Fig. 5) through cam switch contacts |13y and conductor I1| to close an operating circuit for a forward" 'relay- 251 yia'normally closed starting position contacts 253 and conductor 254 to battery 250. circuit actuates forward relay 25|, energizing `motor starting ycoil 255 via conductors 256, contacts 251, 258, closed, with power line contacts '259 on this relay, which also serves to close its contacts 200 4to energize the main motor field coil 251 via conductors 262 from the same power line, at the same time, thus starting motor 1.21, which rotates the gang condenser drive shaft 1.20 slowly through reduction gear means 1,22.

Energization of the main motor coil .261 as aforesaid also simultaneously energizes the solenoid 2163, in shunt therewith, -of la brake 261, which is normally urged by spring 265 against brake drum 2166 on the motor shaft, to hold the latter against rotation. As soon as the forn ward relay coil circuit is de-energized, the solenoid 2F53 is likewise `de-energired and brake Zidrops back instantly and stops the motor 121 and the associated rotors of the gang tuning ccndensers -1 11a, etc.

When the gang condensers `are disposed Aat starting position, tuned to the call channel, fan end-position cam arm 261 on shaft 120 holds `the starting switch contacts 253 closed vat 268, but as soon as the shaft begins turning the =condensers through the tuning range, contacts 253 open and their circuit is shunted via'conductcrs 254, 25.3 and toggle switch contacts 2691i held closed by toggle 210, so that the forward re lay will hold up until `the condenser rotor drive shaft 120 is turned through the entire tuning range (assuming it does not stop .for an idle channel beforehand), whereupon the cam arm 2151 will trip toggle 21!! into the .opposite position. thus opening forward relay `shunt contacts `Zlio: and dropping out this relay 251.

Such `action of the toggle closes reverse superv-isory contacts 212, closing circuit via conductors 213 from battery 250 to one terminal of the .reverse relay 214, the power circuit from battery 2150 being completed. via .conductor `254, ltoggle switch contacts 215 closed, conductor 216 to the remaining terminal of the coil of relay 214. Also, conductors 254 and 215 are shunted by, contacts 211 `closed (as by cam arm 251 leaving starting position) to complete the carry-over necessary to permit cam arm 25119 to pass the toggle as it approaches normal starting position after reversal, cam arm 251 .opening the shunt supervisory contacts 211 when the drive shaft, and hencecam arms 251., 2511?, actually reach startn ing position.

Assuming that the reverse relay 214 has been energized as aforesaid, reversal of the motor is effected through closure thereby of contacts 280, power line lead 281, conductor 282, 'for the main motor winding, and power line lead 283, contacts 284 closed, conductor 235, coil 255, conductor 235e, contacts 251 closed to power lead 281,.'for the starting coil 255.

It will be observed that alternate forward and reverse motion of the tuning motor 121 will coning position contacts 211 closed, whichever of said contacts l215, 211, happened to be closed at the time, since they open and close in reverse relation, whereby the motor will always be stopped at its normal starting position whenever cam contacts e (Fig. 5) are closed, as by return of the call signal selector means to normal starting position.

In Fig. '1, there are disclosed certain details of the automatic, central exchange, call coding transmitter which is generally indicated at 0 in Fig, '2. This device includes a plurality of audio -frequency signal tone sources, 300, 300e, 3001) 300i, there being *ten such tone sources corree `spending to Vthe ten digits (counting zero as a digit), each generating a call signal frequency ranging from 300 cycles to 2750 cycles, as heretofore explained.

One output terminal of each signal frequency generator aforesaid is connected in common to one of the two call channel leads 11x. The remaining tone source output leads 30am', 300m, each terminate in a corresponding set of brush contacts 302, 3020 305D 3053i, all carried on a bail 303, which in turn 'is shiftably carried on `a rock shaft 304, urged into the normal position shown by spring means 300e, wherein each of the said brush Contact sets 302, 302e, etc., is shifted axially of the rock shaft (toward the left, Fig. 1), with respect to a corresponding number of operating cams 305, 325e .3051, arranged in three horizontal rows or sets on an arcuate mounting panel 30B, such that Ieach brush contact, when aligned as hereu inafter explained, can engage any one or all of three cams disposed Aalong its arc of travel.

In the normal position shown in Fig, 7, the

'brush contacts 302, etc., are shifted or `offset with respect to their respective columns of cams 305, 305e, etc., so as not to engage the latter when the rock shaft 304 is rocked downward, by depressing handle 309, but when said handle is released by the operator, spring 304a urges shaft v304 in an anti-clockwise (upward) direction.

The bail 303 is coupled to the rock shaft by pin means 3 I0 engaging in spiral grooves or worm tracks 311 on the shaft, so that downward or clockwise `motions of the `shaft tend to shift the pins 310, and hence bail 303, and hence brush switches 302, etc., toward the left out of alignment'with `cams 305, but upon reverse or upward motion of the shaft, the worm coupling 310-311 shifts the bail and contacts back into alignment with the cams.

The cams 305 Vconsist (Fig. 8) essentially of arcuate shoes carried on plungers 312, normally urged by individual springs 313 to raised position with shoes or cams 305, etc., out of the path of the corresponding brush contacts 302, etc.

Bydepressing any of the plungers 312, the same will be locked by a catch 314 in the slot 315 of a lock bar 316, which is shiftable laterally of the axis of the 'plungers against its normalizing tension spring BIT.

As depicted in Fig. 8, Vthere are three of the same digits, 1, 2, etc., shown in each column of keys or plungers, as indicated on the knobs 318, 318e, etc., there being ten digits (inclusive of zero) in each horizontal row across the unit, and three of the same digits in each vertical column, from which selection of numbers, as heretofore stated, one thousand combinations of three digits at atime may be made.

After a call number has been set up on this coding device, the plungers may be normalized or released by depressing a clearing button 320 (Fig. 8) having a non-latching cam nose 32| which engages edge 322 of a corresponding slot to shift the latch bar 3|6 to the left and free all depressed plungers.

Operation The exemplary installation shown in the drawings, particularly Fig. 2, contemplates 100 trunking channels, and one call channel, and therefore there would be provided 100 channel converter units each identical (excepting as to operating frequency) Yto the converter units shown to the left of the input transformers I3, l3nt, in Fig. 2. In addition, there will be at least one more such channel converter for call ,signallingV purposes to transmit substation call signals from the coding device 8 at the switchboard via conductors l lx and input transformer l3y to modulate the frequency ci the call channel carrier.

In addition to the aforesaid channel converters, there will be individual receiving circuit units called channel separators corresponding in number to the Ynumber of channel converter units, not counting the call channel converter.

Each channel converter provides a transmitting channel, and has a corresponding channel separator unit, providing a receiving channel, looped in with it to the same switchboard jack terminal.

The frequency of the call channel is selected at 500 kc., and the remaining 100 channel converters operate on frequencies separated by an interval of 10 kc. (see Fig. 1). Thus, channel No. |00, for example, would operate at 510 kc., channel No. 99 at 520 kc., and so on, so that channel No. would accordingly operate at 1500 kc.

The operating frequency of each channel separator unit is likewise separated from the other by a frequency interval of kc., and, as depicted in Fig. l, channel separator unit No. |00 may operate at 1000 kc., channel No. 90 at 1020 kc., and channel No. l, accordingly, at 2980 kc.

The control link station operator plugs the usual telephone set into any of the jacks I2 and is thereby connected for two-way'communication over the corresponding channel converter and separator section of any of the 100 trunking channels.

If it is assumed that a regular non-mobile telephone station has called in for connection to a mobile substation whose assigned call number is 130, the central operator sets up the number by pushing the plunger knob 3|8 numbered in the lower or hundreds column on the call selector shown in Fig. '1, and in the tens row the knob numbered 3 is depressed, and nally in the units or top row the knob numbered 0 would be depressed. thus lowering the correspondlng operating cams generally indicated at 305 into operative position, whereupon the` 'operator would pull handle 300 (Fig. '7) downward and release it for return by spring 304a ata rate regulated by conventional governor means 325.

The return motion of the associated shaft 304 shifts the brush contact bail 303 to the right so that the brush contacts generally indicated at 302 will be operated by engagement with such of the cams 305 as have been depressed by the operator. In this example, the brush switches corresponding to the frequencies assigned to the call numbers |-3-0 would be so actuated in succession, connectingk tone momentarily from the tone sources 300 via conductors 300m, brush contact 302 to leads ||.r which connect with input 16 transformer |31/ (Fig. 2), thereby modulating the call channel converter with a rst call signal tone at300 cycles.

As the bail 303 'continues its upward movement, brush switch 302a would then momentarily connect tone from source 300a via conductor 300cd` to the call channel input leads Il, so that the call channel converter would transmit a signal at 492 cycles, and nally brush contact 302i would be actuated to connect tone from source 300i via conductor 30mm to leads Hx, causing a call signal at 2750 cycles to be transmitted.

Referring to Fig. 2, the foregoing call signal frequencies would be impressed in succession upon they 500 kc. call carrier generated by the call channel converter associated with leads Hz, and the call carrier, thus modulated, would be impressed in turn (Figs. 2 and 3 read together) upon the central station U. I-I. F. transmitter through the injector coil 24h, channel mixer 42, wide-band amplifier 46, modulator 46a, and thence upon the main U. H. F. carrier through the U. H. F. amplier designated in the block diagram.l

All mobile substations being tuned to their normal stand-by call channel of 500 kc., the main carrier would be received and demodulated by the means heretofore described, at all stations, and the call signal frequencies ultimately caused to traverse the filter circuit means |44 (Fig. 5) at each such substation.

Assuming that lters |44, numbered |-2-3 in Fig. 5, were peaked or tuned to audio frequencies at 300, 492, and 2750 cycles, respectively, then the selector tube |53 would have its grid |52 excited by three successive call signal impulses, the rst of which would cause relays |55a, |55b, to pull up at once, but whereas relay |55b would quickly release at the cessation of such rst impulse, relay |55a, being slow to release, would tend to hold up long enough for the next or second signal impulse to arrive. Meanwhile, actuation of relay "|5512 would energize ratchet magnets |51 to advance the ratchet means |49 one step, causing contact arm |48 to lodge on lter contact #2. If the second call signal is of proper frequency to pass lter #2 and arrives at its properly timed interval, before relay |55a has had time to release, then both relays |55a, |551) are again impulsed, causing slow relay |55a to continue to hold up, and causing the ratchet mechanism to advance contact arm |48 to lter contact #3.

When the slow relay |55a rst pulls up, its contacts |59 energize the locking magnet |60 to pull locking dog |64 into locking position .so that the ratchet mechanism cannot return to normal position. If, however, the second or third call signal impulses are not properly received thereafter, as explained, then relay |55a releases, deenergizing the locking magnet |60 so-that spring |64a restores the locking dog and frees the ratchet means |49 for return to normal starting position by spring |4912.

Assuming that the three call signal impulses are, however, properly received, the selector arm |48 will be lodged upon contact #4, and selector cam |69 will close contacts |13, thus energizing the forward tuning motor relay 25| (Fig. 6) via conductors |10-I 1| thus connecting power to thevstarter and main windings 255, 26| for motor |2| at relay contacts 251, 258, 260, whereupon gang condenser shaft |20 rotates the rotors of 17 condensers4 lil 1a, I lila, 203 (Fig. 4:), thus progressively tuning both the transmitter and receiver of' the called substation .over the trunking frequency range, `as heretofore .explained .in detail. Meanwhile, locking magnet .I Blholds up by clo.

sure .of cam .contacts |62a and` relay contacts 59a on .the slow relay.

At `the central omce .(Fig; v2:), `Aidlechannel tone .from source conductors `90 isimpressedwia conductor 9i .and rel-ay. contacts 92, normally closed, [condenser 93., transformer windings 14a, .'M, upon the drop or jack connections .1i-*16101* channel No. l, and .consequently ,uponthe input transformer 13 Vfor the corresponding lchannel converter, and filter #A (Eig. .4) at' the substa. tion .being tuned .to the .frequency of this idle tone causes the selector re1ay..tube .to f'be excited so that relays 155e, IEb are again impulsed, resulting'in a further advance of vcontact arm :M8 -to contact #.atvurhich .position-cam con .tacts M3 are again .,open, .dropping `out .the .for.- ward motor relay 25| (Fig. -stopping motor '122i instantly, through the agency .of vbra-ke 264, .whose solenoid winding 2M viscle-energized at-this time since it is in parallel with motor .winding 26].

' Thus, ,the substation is now tuned to an idle :tnunking carrierfrequency.

,As a result of cam fI69,.(Fig..-5) reaching ifth position as aforesaid, cam contacts .Iz'lare now A loSed,..con-nectng .power yia-fconductors'illil lto yenergize Vtransmitter power relay il El B, .closing .con- :tacts AI'lBa to .connectxpower-to ythe.transmitter power pack H9, `thus conditioninglthe substation transmitter for .operation 1n addition, the-clos.- A.ing of contact iZgbkeeps :the locking :magnet energized and ,locks `the .selector inmosition =5-.

Cam i619 also .atthis time @closes cam .contacts l-Bil, energizing .motor L82 .of :the automatic ridentification transmitter wia lconductors :ta-l ,and zthis causes the :magnetic recording .loop |53. :to-abe passed through the field of pick-up coil 1184,50 .that'the substation transmitteriis modulated with Athe recorded .identification data via Amicrophone lead 1285, innutztransformerrlll :(Eig. .41) andthe associated larripliiying .and modul-atingstages :I-, i318, 19.0, lgflzfor impression vofthe-identiicati.on recording on the trunking ...carrierfgenerated'by the oscillator :means |,9..4.|98., .and-antenna couoline 18.311, 3for radiation tromfnthgexsubstation antenna..

AThe central :link station `foiferator .receives the substation carrier ouerthe channel :separator unit No. .l 4Fig 2) :in :this 1example,- :the @uniting-fear.- rier .being picked: up by` antenna Afl.; amplied throuchuradio .irequencyzstaseMhfmixed inl-converter stage 48 Withthe 'frequencyof fthe :master oscillator 4.9 to provi-dee nrst intermediate carrier frequency., .distinct from :the-other trunkillg ,carrier frequencies but still bearing the Noiee modulations from the ,identication device :o ffthe substation.

The aforesaid intermediate or trunkingrcairlier is then Vtransferred via injector coil .5m :to .the ,concerter stage .5.2 for channel No. 1|,..p10viding affurther intermediate frequency whichlis amplied instage ed, demodulatediin diode circuitlu; 68a,l8,8, and :the D. C. component fof;the;,recti.ed carrier impressed upon the ...grid :89 of Athe dl'e channel relay tube .(1ig.:2)..`

.Asa resustof .voltagethus applied :to zrelayftube grid fils, idle channel" frelay ,winding 85 `ais loner,- gized, causing .contacts 19.2 to openy `liftingzthe idle tone fromnthe jchannel, .and zfclosing foontacts :83, 83a, to :illuminate .'busy lamp 80 via conductorA .82, .thus .signalling the .central operator that a call is incoming, whereupon theoperator plugs-in on .channel No. l; listens to theidenticaftion data, which will preferably bea -vocal'records ing of the :substation .call number, .in .thisA example IHS-Alf" and thereby ascertains .thatv theiproner station :has responded. The .trunk carrierfis ,demcduilatedto deliver the voice component sto ,the ackfterminals bythe diode Acircuit :Sii E8, 69, and transferred =Via .condenser "H, .conductor '12, t0 gridfiaof. the audio lamplifier tube whoseoutput is .connected .through transformer. means il dea-.14a to the jack .terminals I2.

. The .central .station operator having 4thus determined that ycominunication is established with the yproper substation, interconnects the calling and-.called stations at the .jack terminals `and closes-fswitch 2.08 at the switchboard, thus connecting'a` go-ahead or connecting signal of audio At1'1eoluency from source conductor 209 -v-ia. jaclccontact :I2y .to Athe .inputleads I I"of this channel, -and y:this frequency passes -lter #5 V(Fi-'g'. 5) -at tthe substation, Acausing .the selector .contact arm,.i118 .to-be .advanced tosiXth and -nal posi'- tion.`

When thus Aadvanced `by connecting tone,'tlie selector` switch contacts 2-l2wshunt the contacts lfi Etnow. open again) to lhold iup .the transmitter .power .relay H8, contacts `-I 315aconnect the'hand telephone setl 4receiver `with the output ofz .the audio-detector amplier stage =|f25via.conductor .135, -and .terminal lb while .contacts 162e shunt contacts 1.6219 .andicontacts A21| 5 .close an operating circuit, through telephone set contacts 25l1.nor.

inally closed, to .the signal .or .buzzer :2il8to :sum-

mon the. subscriber, who .lifts ther instrument, .causing contacts 2H to .open and stop ithe buzzer, as fanincidentto .raising v.cradle plunger 225, .which alsoactuates .selectorfswitch levers 226,221, .without eect'atllthe time, since. .notch 230aion .ratchet Wheellbsisawayrom dog 229. However, clockwise motion of lleverewheel 228 `upon Alifting of lthe hand-set, -brings the .cam projecting from Itlfieface ofwheel`2281into position relative to the armdliila so :that when :the :hand-"set -is inally restored and cradle lplunger descends,- leverwhee'l 2228"will rotate Aanti-clockwise, causing 'this cam .to operate arm 19M-to .the `right toopen contact i90 Avtemporarily .and thereby de-energize the :locking .magnet 1160. Locking dog .|64 .is..reA tracted by .spring .|64a and vthe selector returns unopposedito positions! .f

As a-:Eurtheruincident to .raising of the cradle plunger 225, microphonecontacts220:c1ose, connectingthe zhandesetmicrophone -at terminals 22.1, 222dngcircuitwith microphonetlead L85, The called subscriber. is ,nowmeady to talk.

When `the substation hangs up by reseating the handeset ltocdeinress'y cradle plunger 2125, .the :lever means 226, 221, 228, 229 will reset the selector cam tov .starting ,position .as heretofo1e..described, normalizing Aor Arestoring all circuits theretofoce setfup,:and ,closing .tuning motor :norma-licorrtacts tima lto .aetuate the. .motor reverse relayfxzl wie.

conductors 121B., |:'l2,.causing a return @of .ithegang condensers to starting .position with .the sub.- stationzreceiverftuned .again to fthe call channel frequency .M5500 kc.

AG11'a=nnell\io.. Itwill again A:be designated #fidlei byextinction ,of ybusy lamp .80 and application of fidle :toneto this channel bydroloping .outfoi fid1e.=chennel relay 18,4 .-(Fig, 2.) opening contacts 2.3.- .;lia, and closing Veontact-s 92.

fIn fthe vevent the .substation initiates fthe callJ raisins .fof `.the hand ytelephone .Set factuates Ffle.

) lever means 225, 226, 221,' wheel 223, to cause dog 229 to engage in notch 23M and rotate ratchet wheel 230i)` clockwise to move selector contact arm |48 and cam |69 to fourth position, at which cam switch contactsll close to start the tuningmotor, under control of means V15, heretofore described, to test for an idle channel., Locking magnetl would also be energized through contact cam switch 152 to hold -up the selector switch in fourth position by closure of `contacts |620..

The operation fromthis point on, goes forward as in the case of the call just previously described. When an idle channel is found, the selector Switch advances to position fi'ive, causing transmission o'f the identification data of this substation; the I central operator, upon responding, effects transmission of the connecting signal by operating switch 288 (Fig. 2), which sets the selector and cam` switchcontacts to the condition of sixth position, and the Asubstation is ready forV communication with the central operator and any called stationY connected through the central board.

A. While have illustrated and described the preferred'form of construction for carrying vmy invention into effect, this is capable of variation and ;modiication without departingr from the spiritof the invention.` I, therefore, do not Wish tozbe limited tothe precise details of construction set forth, but desire to avail myself of such variations and modifications as come within the scope of the appended claims.

Having thus described my invention, what I claim as neWand desire to protect by Letters Patent is:

l. -Infa communication system of the class described, inV combination, an ultra high frequency transmitter and receiver, a plurality of channel converters generating a plurality of transmitting trunk carriers and each having, operatively-associated therewith a channel separator for receiving an incoming trunk carrier of frequency diff- -ferent fro-m the corresponding transmitting trunk carrier, whereby each saidchannel converter and corresponding channel separator comprises means for two-way communicatiom means formodulat-` ing each channel converter individually with voice frequency energy, said channel separators includingv means for demodulating the trunk carriers received through said channel separators, means coupling said .channel converters with said high frequencytransmitter, means coupling said channel separators with said high frequency receiver, means cooperable with saidchannell converters for. modulating the same` with an vidlesignaL means'co-ntrolled by the trunk carriers rece-ivedby said channel separators for rendering said idle signal modulating means ineffective for the corresponding channel converter when the trunk carrier isreceived by the corresponding vchannel separator. y

12; In a communication system, means for generating an ultra high frequency main-carrien means for generating a plurality of outgoing subfrequency trunk carriers, .their frequency-'being a small fraction of the main carrier frequency, and spaced approximately l0. kilocycles apart, means formodulating said trunk carriers with voice frequency energy, means for superimposing all outgoing trunk carriers upon said main carrier, means for receiving an incoming vultra high frequency carrier, means cooperable with said receiving means for selecting incoming trunk car rier frequencies at 20 kilccycle intervals within thefra'nge of said ultra high frequency carrier and for demodulating s-aid incoming trunk carriers,l meansv for modulating said main carrier with various call signal frequencies, and with an idle signal frequency, and with a connecting signal frequency, vmeans for connecting an operators telephone setl'selectively with one each of said outgoing and incoming trunk carriers in pairs for two-way communication thereover, together With substation apparatus including a transmitter and a'receiver respectively adapted to operate at frequenciescorresponding to any said pair of trunking-frequencies, means for tuning said substation receiver and-transmitter successively to any said pair of trunk frequencies, means actuated under control of said call signal frequencies received by the Vsubstation receiver for automatically tuning saidlsubstation receiver and transmitter to a pair of said trunk frequencies, one of which is modulatedby said idle signal'frequency, and means at said substation actuated under control of said connecting signal frequency received over one of the pair of trunk carriers to which the substation receiver is automatically tuned as aforesaid, for establishing Y connections at said substation for two-way communication over said pair of trunk carriers. J Y

3. In a communication system of the class described whichfinclude's means for transmitting a plurality of outgoing trunk carriers and receiving a. plurality of incoming Ytrunk carriers, -means modulating said transmitting trunk carriers With an idle tone, means coupling said outgoing and incoming .transmitting and receiving means in pairs for two-Way communication, indicating means associated with each said pair of transmitting and receiving means operable to indicate the same as bu'sy, and means under control of an incoming trunk carrier for effecting operation of the corresponding indicating means and rendering said idleV tone modulating means ineffective I' f orthe corresponding outgoing trunk carrier when the corresponding incoming trunk carrier is received. 7 v Y "4. In a communication system of the class described which includes a broad-band ultra high frequencytransmitter operable over a first frequency-band'and a broad-band ultra high frequency receiver operable over a second frequency band different from the 4irst band, the combination of a'plurality of means generating a plurality of outgoing trunk carriers of distinct frequency, means for separately modulating said trunk carriers and modulating said transmitter with all trunkcarriers, means c'oioperable with said receiver for selectively demodulating a plurality of incoming trunk carriers received thereby, means linking an v outgoing trunk carrier generator means with incoming trunk carrier demodulating means'tof provide two-way communication channels, 'means normally modulating outg-oing trunk carrierswith an idle signal, and means actuated by incoming trunk carriers to eiect removal of the idle signal from the corresponding outgoing trunk carrier.

5. In a communication system of the class described, substation apparatus comprising an ultra high frequency receiver operable on a rst frequency, an ultra high frequency transmitter operable on a second frequency different from the irst,l means for simultaneously tuning said receiver and transmitterft'o" operate at any of a plurality of sub-frequenciesdiffering respectively for the receiver yand transmitter, means actuated by a combination of predetermined received call signals for'starting said tuning means, means actuated by apredetermined received idle sigarrows 212 naif for stopping. said. tuning. means, at a tuning frequency' at whch.said2idle. signal: was received, and., means actuated: by apredetermineda received connecting signalf tor' giving'- a signal atV the substation;

(i.` A. 'radio communication system comprising a central# station including. an ultra high frequency transmitter and arr-.ultra high frequency receiver each. operating on. a. distinct ultra high frequency band; m-eansproviding a plurality ot outgoing trunk. carriers all.' superimposed uponr said tra-ns mieter carrier'V means providing.. a pluralityv et in coming: trunk carrier demodulators each` tuned toda frequency distinct from that of anyf outgoing trunk carrier and'. all energized.fromsaidlreceiver; means providing a call channel carrier." superimposed. upon the transmitterl carrier, means modulating. eachoutgoing trunk carrier- With an idle signal., together with a plurality of subst-'ations each including a transmitterprogressively tunable over the frequency range of' saidincoming trunk; carriers, a' receiver progressively tunable over the frequencyrange ofj said outgoing trunk carriers and said call-channel carrier, meansace tuated by a call signal received at saidsubstation aty saidA call channell carrier frequency for-startingsaid' tuning means ofl thereceiver andg transmitters; means actuatedL bysaid idle signal reoeived at the frequency of' one'of said outgoing carriers `for stopping said tuning means of the receiver and transmitters with the substation receiver tuned-` to s-aidy last-mentioned' frequency; andsthesubstationtransmitter tunedv to the corresponding distincttransmitterfrequency, means at thesubsta'tionfor modulating the transmitter thereof with station id'entiiication dataauomaticallyupontuning by idle signal as aforesaid, meansv at said'eentral station forI- transmitting a connecting signal at the frequency towhich the substation receiverl is tuned# saidAv idle` signal; means at said substation actuatedby reception of said-connecting signal to stop said identification modulation, tu, give asignal at the substation, and to connect said' substation transmitter and receiver-for tyre-Way4 communicatiom with said central station at the tunedsfrequencies de'- termined bythe idle signal as aforesaid.

7. Apparatus as deiin'ed in claim 6- in which said central station transmitter is further" pro.- vide'd, with, means for modulating; said rstirequency with aplurality of subyfrequencies, and means for modulating,` the suing-frequencies: with idleiton'e andconnecting tone. of. predetermined frequency; and, said. substation' apparatus; isfurther characterized by the provision of: means coopera-.bles-` with said; selective means responsive tothereception of saididle. toneffor actuating said selector switch means to still further ad.- vanced positionto disable saidv tuning means` of themeceiver and transmitter. withthe substation receiver tuned to the sub-frequency at which said' idle tone was received, and. thereafter to eiefctvstilltfurther advance rof said` selector; switch meansr responsive to .reception of. said connecting tone by said selective. means, to'v connect said substationY transmitter andreceiver with: substation telephone equipment. forv two-Way communication thereover.

8. In a communication system of the class described including a central station receiver and a transmitter emitting a main carrier modulated by a call channel carrier and a plurality of subfrequency trunk carriers each of the latter in turn modulated by an idle trunk tone, means for removing said idle tone, and means for modulatreception. oi' said'V connecting. tonelto connect said;

transmitter', said? receiver, and said?l telephonelset for. two-way communicationwith' said central-f station ati frequencies lying Within the rangehot said' main. carrier.;-` said'l substation transmitter at allf times being. tuned toa non-interfering fre#v quency different from frequency to` which thesubstation receiver is tuned;

9;y In; an ultra. high` frequency carrier com.- munication. system, a centralM oilice ultra high frequency main carrier generator; means for' generating andbmodulating a multiplicity off carriers,- means for: modulatingA themain carrier with saidA sub-carriers;. means modulating idle subfcarriers distinfctively; substation apparatus includ-ing' a. tunable receiver. and transmitter; modulation.. controlledf means for starting. a, tun-i ing.` operation of. said. substation apparatus to locate anidlesub-carrier; modulation-controlled means for stopping, saidtuning: operation when theA substation apparatus. is tuned to a-Jsaid-Jdis tirictivel-ymodulated: sub-carrierg means` opera-te ingfautomatically at. the substation to transmit an identifyingsignal: to the centrali oli`ee= when said. tuning. operation is. stopped` as-l aforesaiclfg.. modulation-.controlled means at'.- the` substation for'interruptin'g saidfsignal transmission and give ing-,1a subscriberssignal; and means-at saidoen tral cnice for. modulatingsaid-sub-carriers. vvitl-iy controlA modulationslfor actuating the aforesaid modulation-controlled means.

1.05. Improvements inv communication systems. of? the classavvhich include a central oliice ultra high frequency emitter and receiver modulated withsubg-frequencies to provide amultiplicity'of twee-way. communication channels with mobile andi 'xedfi substations, said improvementscom`` pri-singa; substation transmitting and receiving nimma-tus:l including means. for tuning said: ap#- paratus-f over the frequency range-oi said chan@ nels, means normally?` tuning said apparatus` to aycallifrequency channel, meansiactuated by signalsrover; saidlcall channel for setting said tuning; means-into operation, means actuatedfby idle signala onL a selected-. idle communication chan-nel toiwhiclrsaidsubsta-tion.apparatus becomes tuned as=aforesaid for stopping saidtuning meansl with thasubstation.apparatustuned to said last-mem tionedl` channel; means actuated automatically upon'zstopping offthe tuningvaforesa-id to'eiectV transmissioniof anidentiiicati'on signal from said substationY over said Selected channel; centralioflice controlled signal means for stopping trans mission ot said identification signal and giving an incoming call signal at said substation and for further conditioning said substation apparatus for two-Way subscriber communication over said selected channel; means at said central cnice for impressing an idle signal on all idle channels; means at said central office providing at least one said call frequency channel; and means at said central oce for impressing on a said call chan- 23 nel signals as aforesaid for starting said sub station tuning means.

11. In a communication system employing ultra high frequency carrier with sub-frequency, trunking carriers thereon, improvements com prising: central office means modulating idle trunking carriers With an idle signal; substation transmitting and receiving apparatus tunable to any said trunking carrier; substation means actuated by predetermined call signal from said central ofce for tuning said substation apparatus successively to each said trunking carrier; substation means for automatically causing said substation apparatus to remain tuned'to the nrst idle signal encountered during said successive tuning; and substation means for automatically signalling over said last-mentioned trunking carrier seized by the substation as aforesaid to designate at the central ofce which trunking carrier has been seized by the substation. Y

12. Improvements as defined in claim 11, fur'- ther characterized by the provision of means at said substation for initiating said tuning operation at the substation to seize an idle trunking carrier, for actuating said designating means, and for transmitting a substation identifying signal over said seized carrier to the central oice.

13. In a radio communication system, a plurality of stations each having receiving means tunable to any one of a plurality of communication channels, the receiving means of each station being normally tuned to a call signal channel, a further station having means for transmitting a marking signal over one of the communication channels and having means for transmitting a signal, characteristic of one of the first stations, over the call signal channel, means controlled by the receiving means at the station corresponding to said characteristic signal and responsive thereto for causing the receiving means thereat to scan the plurality of com munication channels, said last means being responsive to the marking signal transmitted over said one channel by said further station for stopping the scanning of the communication channels bythe associated receiving means when said one channel is reached.

14. In a carrier wave communicating system, means for generating and radiating a main ultra high-frequency carrier, a plurality of channel converters and a plurality of channel separators connected in pairs, each channel converter producing a different sub channel Ycarrier frequency and having means for modulating the main carrier therewith, a wide band receiver adapted to receive a second ultra highfrequency carrier modulated by still different sub channel carrier frequencies, said channel separators coupled to said receiver and means for connecting each'pair of converters and separators inv connections whereby simultaneous two way transmission may be had over the main carrier modulated by any plurality of its sub channel carrier frequencies, and over the secondultra high-frequency carrier modulated by its different sub channel carrier frequencies.

15. In a radio communication system, a main station and a plurality of' substations, a plurality of transmitting and receiving channels at the main station, each transmitting channel producing a different carrier frequency from the others and each receiving channel tuned to a different carrier frequency from the transmitting channels, a pair of transmitting and receiving channels at each substation, means at each station responsive to a particular signal transmitted from the main station over one of the transmit ting channels to successively tune the transmitting and receiving channels thereat in steps, each step tuning said last channels to one of the transmitting and one of the receiving carriers of the main station, means in the substation responsive to a particular signal over one of said carriers for stopping said tuning means when tuned to a pair of said carrier frequencies corresponding to a transmitting and receiving channel of the main station and for indicating in the main station the pair of channels selected, and means in the main station for thereafter completing a communication channel between said main station and the selected substation over the Vselected pair of channels.

16. In a radio communication system, a central oiice,l a plurality of substations, a plurality of communication channels in the central office, eachA channel including a path over which a carrier of a particular frequency is transmitted and a receiving path tuned to a carrier of another frequency, the frequencies of each channel differing from each other channel, means at each station for selecting any one of said channels and signaling the central office thereover, means at the central oflice for establishing a connection to another substation over any other of said channels and for linking the two channels at the central ofiice to provide a two Way conversation link from the rst to the second substation including both of said channels.

l THOMAS I. RESS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,499,081 Smythe et al. June 24, 1924 1,568,194 Smythe Jan. 5, 1926 1,572,756 Smythe et al. Feb. 9, 1926 1,619,228 Williams, Jr., et al. Mar. 1, 1927 2,064,894 Espenschied Dec. 22, 1936 2,064,895 Espenschied et al. Dec. 22, 1936 2,064,896 Espenschied et al. Dec. 22, 1936 2,064,904 Green Dec. 22, 1936 2,064,905 Green Dec. 22, 1936 2,064,961 Tidd Dec. 22, 1936 2,107,168 Tidd Feb. 1, 1938 2,112,877 Beverage Apr. 5, 1938 2,137,023 Monk Nov. 15, 1938 2,152,329 Schussler Mar. 28, 1939 2,156,278 Dekker May 2, 1939 2,188,508 Herdman Jan. 30, 1940 2,298,409 Peterson Oct. 13, 1942 2,325,829 Boswau Aug. 3, 1943

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