US2101668A - Radio communication system - Google Patents

Description

Dec, 7, 1937. J. B. BISHOP Er AL RADIO COMMUNIQATIONiSYSTEM 6 Sheets-Sheet? Filed Sept. 26, 1935 /NVENTORS J. B; B/SHop 'W M. KNOTT B .yg/J

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Dec. 7, 1937. J. B. BISHOP E1- Al.

RADIO COMMUNICATION SYSTEM Filed Sept. 26, 1935 6 Shets-Sheet 3 MNM.

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7, 1937. y J B; Hops ET AL 2,101,668 I RADIO COMMUNICATlEON SYSTEM Filed sept. 26,` 1935 e-shets-sheet 4 J. B. BISHOP /NvENTo/Psw M KNO".

A TTORNEV uw.v 7, 1937. J: B. BISHOP T AL. 2,101,668

v 4RADIO coMMNIcATIoN SYSTEM 6 Sheets-,Sheet 5 Filed sept. 2e, 1935 935.6 Etam E 1Mb www ATTORNEY 75 l937- J. B. BlsHoP T AL imno COMMUNICATION SysTEM Filed sept. 26, 1 935 6 Sheets-*Sheet 6 P 0 H S l B B. `J uuu dzfdm w w No 31 ma wbb wmmwb QU 5S w ma 1% Qu SMS/ m M Klv-OTT l V ATTORNEY.

Patented Dec. 7, 194374.

RADIO COMMUNICATION sYs'rEM John B. Bishop, Bloomfield, e and william M.

Knott, Fairlawn, N. J., assignors to Bell Telephone Laboratories, Incorporated, N. Y., a corporation of New York New York,

Application september ze, 1935, serial No. 42,112

^ 12 claims.

This invention relates to radio communication systems and particularly to two-way radio communication systems and control circuits therefor.

An object of the invention is to provide a system for two-Way 4radio communication which will meet the requirements of reliability, economy of operation, simplicity of control and the like, essential to a two-way communication system for commercial operation.

w One obstacle to the use of radio for communication is the lack of dependability. This fault is partially an inherent characteristic of radio Y transmission and is due to atmospheric disturb.

v ances, lskip distance effects, and the like. Since as far as our present knowledge is concernedthese difficulties must be accepted, it is necessary to adopt some method of overcoming their effects. It is well known that atmospheric disturbances while present to some degree at nearly all frequencies, do not affectv all frequencies equally.

Further, skip distance effectsv can be made to serve a useful purpose for carrying a signal over a maximum distance with a minimum of power. To take advantage of these conditions it is necand receiver and if the service is to approach the reliability of other types of communication service such a shift of frequencies should be ac-A complished with the least possible delay.

A particular object of the invention is to prov ide a radio transmitter which may be operated on lany of a number of frequencies and which can be readily shifted from one frequency to another in a minimum time and with a minimum of control operation.

Another object of the invention is to provide a radio transmitter which can be mounted at an isolated point andv operated unattended except for controls from a remote point for turning von and off `the power and automatically and rapidly controlling the frequency.

`Anotheryobject of the invention is to provide means for reducing the consumption of power in remotely controlled radio transmitters.

Another object of the invention is to provide interlocking control means between a radio transmitter and a radio receiver'so that two-way communication may be carried on without interference in the receiverfrom the local transmitter. These and 9121.1?? objects of the invention have essary to shift the frequency of the transmitterA (Cl. P18-44) been accomplished by the arrangement to be described in connection with the attached drawings, which, when arranged as shown in Fig. 7, show schematically one embodiment of the invention in a combined radio transmitter and receiver for 5 two-way 'communication by telephone or telegraph.

Radio transmitter The mechanical structure of the radio transmitter is of the type disclosed and claimed in the patent of H. D. Wilson, No, 2,077,160, issued April 13; 1937, and comprises five removable chassis located in a vertical arrangement from bottom to top as follows: Oscillator chassis Bill, first 15 buffer amplifier chassis 5H), second buffer ampliiler chassis E20, modulating amplifier chassis 530. and output circuit chassis 560. Each of these ve removable chassis is equipped to accommodate as many as ten individual plug-in units which may be selected and adjusted to operate at any carrier frequency within the desired range. The oscillator chassis accommodates up to ten quartz crystal'plates Gli and a like number of oscillator coils SI2. (In each case only the first and last of the series of ten are shown). The rst and second buffer amplifier and modulating amplifier chassis each accommodate up to ten tuning units,.0il, Sil and 53|, respectively. The output circuit ,chassis is arranged to provide for ten tuning coils 5M.

In addition to these removable chassis the transmitter houses the mechanism which is actuated by the teelphone dial 620 to select one of ten elevator rods 605. Each rod actuates a series of bell cranks such as 608 to closel switches in the various chassis completing all the neces- 0 sary circuits for setting up a particular frequency. The first and second buffer amplifier stages are sometimes used to amplify the frequency generated by the crystal oscillator and .at other times one or both are used as frequency doublers, depending upon the carrier frequency desired. In this Way, for example, crystal frequencies ranging from 2000 to 4525 kilocycles serve to yield a range in output frequency between 2 and 18.1

megacycles.

In addition to the radio transmitter circuit proper there is provided, as shown in the circuits 9,f Figs. 3 and 4. a power supply, voice frequency 50 amplifier and control circuit. The power supply circuit includes necessary rectiiiers for obtaining from an alternating current source all the power voltages including plate and grid bias and filament heating current together with a rectifier for obtaining direct current for the operation of the microphone and all control relays.

Radio frequency circuits Before going into the details of the operation of the control circuit of the radio transmitter, the

operation of the radio frequency circuit of the transmitter will be brieiiy considered. As indicated above, there is employed in this equipment a crystal oscillator, two successive stages of intermediate power amplification or frequency doubling, a modulating amplifier and a power amplifier. When M. C. W. telegraph or telephone transmission is employed the modulation electromotive force is applied to the plate and screen of the modulating amplifier tube 532 which immediately precedes the final or power amplifier stage employing a three-element amplifier tube 542. For convenience in describing the circuit let it be assumed that the switching equipment has been operated to select the first or A channel so that all of the switches 60|-A,

602-A, 50i-A, 502-A, 50S- A, 504.-A, S05-A, 50B-A, 50`|A and 508-A have been closed. Switch 60|-A completes the grid circuit of the oscillator tube 6|3 while switch 602-A completes the plate circuit for the same tube. The plate circuit of this oscillator is coupled to the grid circuit of the first intermediate power amplifier tube 5|2 through the coupling condenser 6|4. The tuning unit 5| l--A connected in the plate circuit of the tube 5|2 serves as the complete potential.

tuned circuit in the plate circuit of the tube 5|2. If this stage is to function as an amplifier the circuit 5| I-A is tuned to the crystal frequency. If the stage is to function as affrequency doubler the circuit will, of course, be tuned to double the crystal frequency.

The output of this stageis coupled to the grid of the tube 522 in the second intermediaite power stage through the condenser 5|3. Connected in'the plate circuit of the tube 522 by means of a switch 502-A is the tuned circuit 52|-A which functions for this stage in a similar manner to the circuit 5| I-A of the previous stage.

The output of this stage is coupled to the grid of the modulating-amplifier tube 532 through the coupling condenser 523. Connected inthe plate circuit of this tube 532 by means of the switches 503-A and S04-A is a tuned circuit 53|A which, of course, is similar in its frequency characteristics to the circuit 52|-A of the previous stage. The switching circuit of the modulating amplifier stage 530 differs from that of the intermediate power amplifier stages in that neither end of the tuning unit 53 I -A is at ground This is occasioned by the fact that the power amplifier tub'e 542 is of the three-element variety and requires a neutralizing voltage which is supplied to the lower end of the tuning unit 53|-A through the switch 503-A when closed, a neutralizing circuit of the capacity bridge type being used. When both switches 503-A and 504-A are closed excitation is applied to the grid of the power amplifier tube from the junction of condensers 533 and 534. Switch 505-A shortcircuits a portion of the resistor 55| and leaves the correct amount of resistance in the plate supply in the modulating amplifier tube 532, The

power amplifier stage has its circuit completed by a tuning coil 54|-A which is adjusted to properly tune this circuit when the switches 50G-A and 50i-A are closed.

Dialing channels B. C, D, etc. likewise serve to select the proper elevator rods which, in a simi'- lar 'manner to that described above, lcomplete the entire tuning to the frequencies associated with these respective channels.

The transmitter is designed to work directly into a 50G-ohm load and is equipped with ten independent output terminals which connect to the ten output circuits through the switches 50B- A to 50B-J. One additional output terminal 533 is common to all channels. This arrangement allows for ten independent 50G-ohm transmission lines connected to terminals 50 I-A to BBI-J and leading to ten antennae, or one 50G-ohm transmission line common to all channels connected to terminal 533 and terminated in an antenna tuning unit.

In the crystal oscillator chassis 3|0 is located a self-starting synchronous motor 330 and in parallel with this motor on the left panel are two indicator lamps 03| and 332 which are lighted while the armature of the motor 330 is rotating. 12-volt alternating current is supplied to the oscillator chassis from the connection 634 to the grounded connection 333. This voltage serves to energize the heaters SI5-A SI5-J for the quartz crystal plate and also to periodically operate the motor 630 and supply power through the rectifier BIS to operate the crystal heater relays 6|1A SI1-J. As soon as power is supplied to the rectifier circuit by the closing of switch 402, 12-volts alternating current is supplied to the line 394 and the circuit of the motor 630 is initially completed through the upper contact of the crystal heater relay 3H and the commutator 635 associated with motor 530 and the commutator arm rotates to the lower of the two contacts associated with that particular crystal. It thus breaks its own circuit which is not again com'- pleted until the heater relay SI1 operates. When the relay 3|1 operates the motor 530 is again started and the commutator arm moved to the first contact associated with the next heater relay wherel it remains until that crystal has gone through its heater cycle. In this way the indicator lights 59| and 832 function only when each and every crystal heater is properly operating. Should any one crystal'fail to operate the motor 530 would stop and the indicator lights would remain permanently off. When the crystals are all properly functioning in their heater cycle the indicator lights periodically blink. Should any one crystal heater fail the indicator mark on the motor driven commutator 335 will show which crystal is at fault. In the event that a crystal is not used in one or more of the stages such stage or stages may have their leads going to the motor armature bridged so that the indicator clears that point immediately.

Operation of cfmtrolcircuits Power is supplied from the three-phase alternating current mains 40|. As soon as the main power supply switch 402 is closed the alternating current bus-bars of the transmitter are energized through the voltage regulating transformer 403 and the transformers 404 and 405 are energized, transformer 404 supplying 12-volt alternating current for heating the quartz plates in the transmitter over the connection 534. Transformer 405 furnishes f8-volt direct current for aromas of the rst close energizes relay 62|, the 48-volt circuit for the operation of this relay being completed to ground through the contact 633 of the switch 660 and the contacts of the dial 620. i A circuit is simultaneously closed from the48-volt direct current source through the operating magnet 622 of the selector, thereby stretching its return spring.

The instant of first open releases the selector armature by opening the circuit of the` operating magnet 622 so that the armature is then pulled back by the spring causing the brushes of the four contacter groups 64|, 642, 643 and 644 to rotate to position I. Relay 62| remains operateddue to its slow release characteristic and nothing else happens.

The next instant is that of second close. When the selector operating magnet 622 and the relay 62| each again simultaneously receive a pulse of energy which pulls the selector operating magnet 622 up (relay 62| is already operated and thus remains unaltered'in this position).

T he next or second open period follows immediately whence the selector arm moves to position 2 and nothing further happens until relay 62| releases at the end of its slow release period (about one-quarter second). When relay 62| releases 48' volts is supplied throughthe lower armature of. relay 62|: (l) through the third selector bank 643 to relay 624.and through lead 425 to relay 4|3 which is simultaneously operated by current supplied through the rectiler-r'esistance network 401, and (2) through contact 63| of .switch 630 and fourth selector bank 644 to energize the latching relay 603--B (not shown but identical to relay 603-A) As soon as relay 624 has operated, its holding circuitthrough the contacts of the time delay relay 625 keeps it energized, and two'results follow:

(1) Its lower armature completes a circuitfto the elevator rod contactor 604 which is actuated and moves the rod S05-B, due to the operation of the latching relay BB3-B, to its up position and also starts the Ventilating fan 606 which is connected in parallel with the contactor 604.

(2) Through its upper armature 48-volt direct current circuit to the relay 4|3 is additionally closed thus forming a holding circuit for the relay 4|3. This circuit may be traced from lead 425, upper armature relay 624, armature relay 625, lower armature relay 62| to the 48-volt circuit 682.

When the elevator rod contacter 604 is actuated it mechanically operatesa switch 630. The operation of the switch 630 results in the following simultaneous events:

(1) The holding circuit to the latching relay BB3-A is broken at `the contact 63|, the armature of the latching relay 603--B being mechanically held in place due to the force exerted on the push rod 60E-B.

(2) Arm 632 makes contact with its upper contacts completing a circuit through the selector operating winding 622 through the selector bank 64| so that the `selector mechanism automatically notches itself back'to its normal position.

v (3) Contact arm'633 breaks its connection with its lower contact and makes connection with the upper contact preventing the relay 62| from reafter the elevator rod contactor 604 has completed the setting up of one of the 4radio channels.

The 48-volt direct current supplied over the lead 426 by the operation of the circuits described above energizes the relay 4|3 through the network 401 as previously described. 'I'he operation of this relay 4|3 causes the operation of the filament heating circuit contactar 4|| through the circuit completed from the alternating current bus-bars 490 through the inner contacts of the relay 4|0 and normally closed contacts of relays4l9 and 420.V 'I'he operation of the contactor 4|| causes the simultaneous energization, from the alternating current bus-bars of the A transformer 426 (all radio and grid bias rectifier tube filaments). transformer 428 all high voltage rectier tube filaments) and transformer 328 (the audio-amplifier tube filaments) The operation of the contacter 4|| simultaneously with the energization of the transformer 426 energizes parallel connected winding of the time delay relay 4|5 which is timed to operate 35 seconds later. When relay 4|5. operates the bias plate supply transformer 430 for the grid bias rectifier is energized. This circuit may be traced from the alternating current bus-bar 49|, lead 49|, transmitter gate switches 5|9, 529, 639, 549 and 562, rectifier gate switch 449. contact and armature of relay 4|5 to primary of transformer 430 and upper armature of filament contactor 4|| to bus-bar 492. This causes 20()` volt directl current to be produced by the.grld bias rectifier tubes 43| and this appears across the output resistance network 432. This rectified voltage is supplied to the marginal relay 4103 and energizes it.

When relay 406 operates, its lower armature completes the circuit to one side of the high voltage contactor 4|2, provided the switch 439 is closed or provided relay l||`| is energized by the operation of the microphone press to talk button 459 as described hereinafter. This circuit may be traced from the connection of the busbar 49| at the armature of relay M5, through lower armature of relay 408. switch 439 or lower armature of relay (lll to the lower terminal of the winding of high voltage contacter M2. The

upper armature of the relay 408 completes the ground side oi the L8-volt direct current circuit through the coil of the relay 4|4 and operates it. As a result of the operation of relay M4 the following sequence of events takes. place:

(1) Relay 4|3 is short-crcuited through the upper inner armature of relay 4|4 and drops out.-

(2) A holding circuit for relay 4 I4 is completed through the upper outer armature.

(3) A holding circuit of the filament contacter 4|| is completed through the lower outer armatures of the relay 4|4 and lower contact of the contacter 4| I.

(4) The lower inner armature of the relay 4|4 'completes a circuit to the other side of the high voltage contactor 44|2. 'I'his circuit may be traced from the bus-bar 492, through armatures ofy relays 4|3 and 420, lower inner armature of relay 4|4, lead 432, contact 634 of switch 630 and lead 033 tothe upper terminal of the winding of the high voltage contactor 4|2.

When the high voltage contactor 4|2 is ener gized it operates to energize the high voltage transformer 33| which, in turn, completes the necessary high voltage to the plates of the high voltage rectifier tubes 432 and consequently to furnish direct current to the plate of the vacuum tube forming the circuit of the transformer proper. It also provides power to the filament transformer 333 of the voice operated control circuit 300 described later.

The operation just described sets up the circuit for the operation of the transmitter. The other relay circuits will be described later under the headings Automatic control features for push button, and Voice operated control, respectively.

Direct current power supply The three-phase high voltage rectifiers delivering 2500 volts and 800 volts are employed to furnish direct current power to the plate circuits of the power amplifier and audio-amplifier tubes and to the low power radio frequency tubes respectively. Each high voltage rectifier uses three of the rectifier tubes 332, all of the tubes receiving their alternating current plate voltages from the single three-phase transformer 33|. The 2500-volt supply is delivered through the filter circuit comprising 'the inductance coil 334 and the condenser 335 and the 800-volt supply through the filter comprising the inductance coil 336 'and condensers 331. A potentiometer filter circuit consisting of the resistances 33B and condenser 339 serves to furnish aproximately 200- volt direct current to the screen grid circuits of the tubes to the first and second buffer amplifier stages and to operate the hang-over relays of the voice frequency control circuit 300, to be described later.

As described earlier, an independent full wave rectifier employingtwo tubes 42| and delivering a total of 20D-volt direct current is used to furnish grid bias to the power amplifier and modulating amplifier tubes through an appropriate filter circuit consisting of the inductance coil 420 and condenser 433. A potential divider 432 supplies 12o-volt bias through`the filter coil 434 and condenser 435 to .the tubes of the buffer amplifier stages.

Speech input and monitoring circuit Speech or tone input to the audio-amplifier is brought in over the lines 305-306, for example, from the operators control circuit as will be described in detail hereinafter, or may be obtained from a local telephone set plugged into the jack 409 in which case it will be supplied through the transformer 301 to the connections 305-306.

In any event such tone input is supplied to the primary of the transformer 308. When a local telephone set plugged into the Jack 403 is used, direct current for the telephone transmitter is supplied from the f8-volt rectifier 406 through the filter 4 0 and the microphone transformer 301.

A transformer 4|6 has its primary circuit paralleled by a resistor 4|8 connected in series in the plate return of the power amplifier tube 542. The secondary winding of' this transformer is terminated by the rectifier type voltmeter 42| for indicating the modulation level. The terminals to the secondary of the transformer 4|| are also provided for connecting to the 0perator's set as described hereinafter. For adjusting the modulation level a resistance pad attenuator (not shown) may be inserted in the' leads to thevprimary of the transformer 308.

The audio-frequency amplifier comprises two tubes 309 and 3| 0 connected in tandem. The circuit is so arranged that it receives its high voltage power from the 2500-volt rectifier supplied through the resistor-condenser filter 34|. The grids of both tubes are biased by the drop in the plate current fiowing through resistances connected in the returns to the cathodes. The tube 309 receives its entire plate and grid supply from the voltage drop across resistor 3|| which also furnishes grid bias for the tube 3|0. The grid bias for tube 303 is supplied from the drop in the cathode return resistance .343.

A relay 3|2 is provided so that when operated it short-circuitsv the grid input to tube 3|0 through its upper armature and thus prevents the carrier from being modulated. This relay is for the purpose of C. W. telegraph control since its use allows for controlling the carrier by the method of' keying the tone input without at the same time producing a modulated C. W. signal. The relay 3|2 may be controlled either locally when the transmitter is on any channel or automatically when a particular channel is dialed as will be described in detail hereinafter.

The output of the tube 3|0 is supplied through the transformer 342 to the plate and screen grid of the modulating amplifier tube 532 to modulate the radio frequency carrier in that tube.

Voice control circuits A voice control circuit 300 comprising vacuum tubes 323 and 324 and associated relays and equipment is provided for controlling the operation of the transmitter, particularly for a combined transmitter and receiver circuit, by the voice or tone input. Speech input is supplied to the grid of the flrst tube 323 through the transformer 325 which has its primary winding connected in the plate circuit of the first audioamplifler tube 303 in parallel with the primary winding of the interstage transformer 344. The tube 323 is self-biased by the cathode return resistor 32B, the plate voltage being supplied from the 20G-volt output of the rectifier tubes 43|. The plate supply for the second tube 324 is furnished from the plate supply of the associated radio receiver through the connection 321, as will be described in detail in connection with the operation of the circuit. v

Control unit 300 functions in the following manner: When the speech or tonesupplied to the input terminals 305, 306 reaches a predetermined level. say minus 60 decibels, it-then produces a sufficient increase in the plate current of the second stage tube 324 to operate the plate relay 3|3, plate current being supplied from the B battery supply of the radio receiver. When the relay 3|3 operates two events take place:

4l-The grounded armature pulls away from the back contact which is connected through the armature and contact of relay 3|4 and retard coil 3|6, relay 601, to the plate supply for the oscillator tube 6|3.

2-When the grounded armature of the relay 3|3 touches its front contact. the circuit for the windings of relays 3|4 and 3|5 is closed to ground so that these relays are operated. The current/ flowing from the positive 25o-volt terminal of the voltage divider 333 through connection 3| 1,- resistances 3|9, the windings of relays 3|5 and 3|4 CII - volt circuit.

The relays M4 and lli are designed to provid 'l "hang-over" in the operation o! the voice control circuit. 'Ihe relay I4 is held up for approximately 150 milliseconds atterthe armature cirelay SI2 has returned to its normal position by the discharge of the condenser 32| so that it serves wheny operated to insure that the oscillator control circuit does not' become grounded until some 150 milliseconds after the last passage of speech. Relay Il! is given an additional time `delay due to the discharge of condenser 24| to remain operated from 8 to 10 milliseconds after relay 214 has returned to normal and is usedfto prevent the associated radio receiver from returning to an operate condition before the carrier output of the transmitter has been completely suppressed. t

Relay N8 which maybe operated either locally or automaticallyl on predetermined dialed chan` nels is for the purpose oi modulated C. W. carrier control. Its upper amature functions to disable the hang-over relay N4 by short-circuiting the winding thereof and thus allowsV the transmitter to produce a modulated C. W. signal by the method of keying the tone input.

Key clicks are eliminated by the use of the retard coil 218 placed in series with the oscillator control. circuit thus preventing the carrier from dropping or bumping to zerowhen relay 3I4 d returns to its normal position.

. erations.

Automatic control features for ltmslt-lnttton control of carrier d Two time delay relays 422 and 625 are providedV by means of which full 'automatic operation of the transmitter 'may be secured. These relays are controlled by two switches 422 and 628.

-Switch 423 is known as the automatic illament release switch and 6254 as the automatic high voltage release switcha Switch 423 is in series with the winding of the relay 422 so that in the open position of the switch relay 422 cannot be energized. Switch 626 parallels the contacts of relay B sol that even though this relay were operated no effect would result as long as switch 826 remained closed. For full automatic operation of the transformer therefore switch 626 is normally open and switch 422 is normally closed. Both time delay relays 422 and 625 may be timed to operate in a period such as 1 to 15 minutes.

When the transmitting equipment is arranged for push-button operation, it performs two op- Flrst, the outer armature. with the switch 439 open, is in series with the winding of the high voltage contactor 4I2 so that this contactor will V'only be closed when the relay 4|1 is operated by depressing the key 450. In other words for push-button lcontrol the key 45| controls the entire plate supply to the transmitter and hence the carrier output. A be observed that relay 411 in its normal unoperated condition, through its inner amature, allows the 48-volt direct current supply to be applied to the coil of the time delay relay 425` through connection 424. inner armature of relay 4I1, and connection 426. This would result in the operation of. the relay 42| in from 1 to 15 minutes depending upon its adjustment after a amines. Y

,of relay 42B opens the holding circuit to the rel Second, it will lay U24 which results in two events:

l l-Elevator-contact 404 dropsdown, releasing the channel which had been dialed.

2-The return 48-volt circuit through connection 42| is broken .and as the'result relay 4I4 is deenergized andtherefore dropped out. The holding circuit to the filament contactor 4II is 'still energized, however, throughthe back 4contact of relay 4I! so that the illaments of all the tubes inv both units still remain heated.

Summing up then, the action of relay 425 can serve only to drop down the channel which has been dialed in the transmitter and disrupt the 48`volt return circuit to the rectier controls.

, Itis important to note that in the normal opera- 'I'hertime delay relay 422 is energized throughs the normally closed back contact to the' normally closed contact -of the lower armature of the high voltage contactor 4I2. At the end of this l to.

ing oi' the overload relay 419. thus opening the circuit to the coil of the illamentcontactor 4H which immediately removes all lament voltage'.-

As soon as the lament contactor 4| I has dropped out,` the alternating current circuit actuating the 15 minute period relay 422 operates and in closv ing puts'a pulse of current from the 48-volt source through the connection 431 to the wind,

relay `422 is deenergized. Thus the momentary circuit made to the overload relay 4|9 is broken and relay 4I9 returns to its normal (closed) position, and providing relay 62B has previously operated, thev transmitting equipmentl is back to .the condition it originally was when only the mainpower supply switch 402 was closed..l

It is VVimportant to note here that it is immateriai whether the relay 422 operates prior or subsequent to the relay 825. Each performs its function independently of thel other.` This is not true as will be evidenced in the latel` description, in the event that the use of the voice frequency control unit 30d is substituted for the push-button control. (In this latter event relay l 422 must of necessity operate subsequent to relay Returning tothe case in point, namely thel push-button operation, it is seen thatthe total elapsed time over which use may be made of these automatic shut-down features is conned to a time not exceeding fteen minutes (with relays oi.' the character described) Should it be desired to have the high voltage remov'edfrom vthe tubes of the transmitting equipment but have the illaments remain heated, it is necessary only to throw switch 423 to the open position in which case it would be necessary either to manually close the switch422' and wait the delay period of therelay 422 or to momentarily open the main Apower .supply switch 402. t

'Automatic control features for voice operated control of carrier When voice control of the carrier is employed.

through the use of the control unit 300 switch 4321s closed and switch 438 is opened. Closing 4switch 439 by-passes the particular function of the relay 411 which for push-button control use exercises the final control of the high voltage applied to the radio tubes of the transmitting apparatus, current will flow from the 800-volt supply at the terminal of filter coil 338 through the oscillator plate resistor 6H, relay Bill, back to ground through the choke SIG vand the armatures of relays 3M and SII. This current will operate relay $01 at once and cause the time delay relay 625 to be energized from the f8-volt supply lead 682. After the predetermined time of operation of the time delay relay 825, it will operate as earlier described, to drop down the channel and since the release of the channel opens the interlocks at contact 634 to the high voltage contactor M2, this contactor will be released. As soon as the high voltage contactor M2 drops out, the circuit will be completed through its lower armature to energize the relay 422 which will operate after its predetermined time has elapsed and as described in the section .immediately preceding, will operate on the filament contactor lll to remove all power from the transmitting equipment -except the crystal heater circuit and the 48-volt rectifier supply.

Incoming speech, subsequent to dialing and having high voltage applied tothe transmitting equipment, removes the ground return at the armature of the relay Sil and since no current flows in this circuit, relay 601 is released which in turn deenergizes the time delay relay B26 returning its timing mechanism to the initial position. Thus, the operation of the time delay relay 625 commences at the cessation of incoming speech or tone or from the last starting operation in the absence of an incoming signal.

It is important to note in this connection that the start of the time delay relay |22 commences from the operation of the time delay relay 825, rather than from the start of that relay as was the case with push-button control as described in the previous section.

Auxiliary control feature 'I'he relay SI2 associated with the audio-ampliiier may be actuated by connecting the bus 635 to one or more of the ten points on the bank G42 of the selector. This relay is provided only for the purpose .of converting the radio transmitter into a C. W. telegraph transmitter and is used only in conjunction with the control unit 300 as will be described hereinafter in the section entitled, C. W. and M. C. W. telegraph operation.

Similarly, the bus 636 when connected to appropriate terminals on the bank 842 of the selector actuates the relay Sil and is used to convert the radio transmitter into a M. C. W. telegraph transmitter. This connection also is used only in conjunction with the use of the control unit 300 and its operation will be described in detail in the section entitled, C. W. and M. C. W. telegraph operation.

Protective circuit Protective gate switches are applied on the apparatus to insure that the operating personnel is adequately protected against coming in accidental contact with high voltage. For this purpose there is provided a gate switch Il! on the door to the transmitting equipment and switches 549, B39, 529 and 8| which are opened when any of the respective chassis I, l, III or M are removed from their cradles. Bimilarly, gate switches4 I are associated with the rectifier assembly. All of these gate switches are connected in series in circuit from the armature l and contact of relay 4N through which the grid bias rectier transformer 430 is energized.

Two self-restoring overload relays III and I!! are provided to protect the vacuum tube against Switching mechanism 'I'he switching mechanism as shown and described in detail in the copending application of H. D. Wilson, hereinbefore referred to, consists, in brief, of ten rods 80G-A to 80B-J running the vertical length of the transmitter. Cranks, such as 60S-A, for example, one for each chassis switch, are located on horizontal cross shafts mounted normal to the elevator rod. A mechanism to operate the elevator rods is located at their lower ends.

'Ihis mechanism includes the shaft |50 mounted in self-aligning bearings. One end of this shaft passes through an adjusting block to the armature of the large alternating current operated solenoid 604. Mounted on the shaft GIU are a series of clutch collars BSI- A to lil-J and associated lifting arms B52- A to 6524. 'I'he clutch collars are pinned to the shaft "I by taper pins while the lifting arms 852 are free to both slide and rotate on the shaft. Associated with the clutches are small. latching relays BDI- A and 60S-J for actuating the clutches to engage the lifting arms.

The operation of the switching mechanism is briefly as follows: When the arm of the selector switch comes to rest momentarily on one of the off-normal contacts the voltage supplied to one of the'small latching relays 003 causes the armature of the relay to close and draw with it its lifting arm, which slides along the shaft to engage the clutch collar. At the same instant that voltage is supplied to the latching relay I, voltage is also supplied to relay 624 which picks up and in turn closes the 250-volt circuit to the large solenoid elevator contactor 804. The elevator contactor i now closes and in doing so rotates the shaft 050 with the clutch collar and the one lifting arm which has been previously engaged. 'I'he other nine lifting arms merely allow the shaft to rotate within them and remain in their non-operated positions.

The outer end of the lifting rod Il! which has been engaged to rotate with the shaft comes to bear on the lower end of its elevator rod lll and in turn pushes it upward. The elevator rod 605 transmits its upward motion by means of the bell cranks, such as |08, to an axial thrust in line with the chassisswitches such as ill.

At the same time that this is happening the switch arms of the switch 0 have been changed from their normal to their closed position by means of the lever arm mechanism lll. As here- -inbefore described in more detail, this switch `telegraph features by dial control.

performs several functions, one oi which is to remove the voltage lfrom -the latching relay 003 by breaking the circuit at contact 03|. 'I'hese relays are designed for intermittent purpose only and their sole function is to engage the lifting-arm with its clutch, the two being firmly held together bythe frictional load when the elevator rod 805 is raised.

If another channel is dialed the circuit to the large solenoid 604 is broken on the first puise of the dial and the armature of the solenoid falls back to the open position aided by a return spring (not shown) and the load of the operated elevator rod 605. to disengage from its clutch as soon as the elevator rod has reached its bottom stop at which point the return spring 654 on the armature of Automatic C. W. or M. C. W. telegraph operation When control unit 300 is employed the'transmitting equipment may be made to function as a` C. W. or a M. C. W. telegrapntransmitter by operating either relay SI2 or relay 3|0, respectively, and keying the tone input through thel key 218 at the operators control position as Will be described in detail hereinafter. The relays mayjbe operated by the control switch 20d at the operators position, or may be operated automaticallyv when predetermined numbers are dialed.` In this latter case switch dit must be closed and the buses B and 63E are connected to the proper terminals of the selector contacter tt2. As' illustrated contact i is connected to bus 635 and contact 3 to bus 636. Thus, when i is dialed, the set will operate for C. W. telcgraph and when 31s dialed, for M. C. W. telegraph. Switch t'i is closed only for operation of the When these features are controlled by the operators switch 233, 4the switch M5 is kept open as illustrated.

When i is dialed the set will be conditioned for C. W. telegraph operation by the automatic operation of relay 3|2 through the closing of its operating circuit by the contacts on the selector bank iiilZ. When the selector bank M2 returns to its normal position, relay dit is maintained `operated through a holding circuit from lead Md In a similar manner when t is dialed,'connec tion will be made through the selector bank ttt which will result in automatic operation of the relay 3|8, which also has' a holding circuit y Athrough its lower armature similar to relay 3|2.

Thus keyed rtone input in this case will merely result in starting and stopping of the modulated carrier in accordance with the keyed impulses.

A more detailedv description of the keying operation will be found under the title Radio telegraph communication in the following section on two-` consists in addition to the lradio transmitter andits control circuit just described, a radio re- This allows the lifting arm 062A ceiver |00 and an operators control unit 20| which are interconnected with the transmitter 'I'he radio receiver |00 which is shown in block diagram, only the parts essential to the interlocking control feature being sown in detail, is of the typical superheterodyne type employing an initial Vselector circuit |02 connected between the antenna |0| and the radio frequency'ampliiler |00. The output of the amplier iti is supplied through another selective circuit (not shown) to the high frequency detector or modulator |03, the latter being supplied with beating waves from an oscillator |04 for combining with the received waves to-produce intermediate frequency waves which are selectively amplided in an intermediate frequency amplier |00. The output of this amplifier is supplied to the input of the detector H01 which operates not only to detect the intermediate frequency waves to produce audio-frequency waves which are amplified in the audio-frequency ampliiler |08, but also to vrectify the intermediate frequency carrier to supply the automatic volume control circuit iii of the conventional type. For the reception of continuous wave telegraph signals there may be provided a heterodyne oscillator and .detector (not shown). `For a more detailed description of a radio receiver of this type reference is made to the copending application oi H. T. Budenbom, Serial No. 676,135, filed June 16, 1933.

While grid bias supply and plate lsupply are indicated as furnished by batteries i i2 and it@ for simplication in illustration it is understood that such power supply would normally lbe derived from rectifiedv alternating current inl a wellknown manner.

Associated with the radio receiver is a control circuit |20 which may be conditioned by the operation of the key |2| for operation for either Codan (carrier operated device anti-noise) con- .trol or Vodas (voice operated device anti-singing) control. In the case of both types of operation the controlcircuit |20 operates to block the output of the radio receiver to the 'connected telephone station at all times except. when there is an incoming :signal to the radio receiver as will be described in detail hereinafter. This control circuit also operates to prevent the use of the radio transmitter when a signal is being received and also, in eiect, to disconnect the radio transmitter monitoring circuit from an extension telephone circuit when transmission is being carried on. In so doing it prevents feedback from the radio transmitter monitoring circuit to the speech input circuit by way of a twoconductor extension telephone line but allows the operators telephone receiver to be connected at thesame time to both the. radio transmitter monitoring circuit and the radio receiver output circuit in order to lpermit monitoring in both directions of a radio telephone circuit.

The control of the radio receiver |00 to disable it for the reception of radio signals is accomplished by means of relays |09, I|0 and When operated, relay |09 grounds the antenna K |0| through its front contact and opens the ground circuit for the grid of the tube of the CII the connection through its back contact to the grids of the tubes of the radio frequency ampli- `Iier and modulator |03 through the automatic volume control circuit H3 and instead closes a connection for the grids of those tubes to the battery I2 to block the tubes. The operation oi relay opens the connection to the coils of the Silent coil group ||4 so that they act in series opposition preventing transmission therethrough; This transmission control is of the type disclosed and claimed in Silent Patent 1,749,851, March 1l, 1930. Operated -relay opens the contacts and so arranges the connections between the interconnected windings of the transformers oi the group ||4 that these windings are mutually opposed. Thus, no transfer `of energy between the circuits connected through the other windings of the transformers of the group ||4 may be eected. Consequently. passage of audio-frequency current from detector |01 to the audio-frequency amplifier |90 is prevented.

A second Silent coil group 2|| is employed in the operators control equipment to permit the.

operator to monitor simultaneously both sides of a radio telephone conversation of a two-wire telephone extension circuit. This coil group 2|| also serves as an added precaution against objectionable clicks and other circuit noise incidental to the operation of control relays which might otherwise reach the subscribers telephone receiver. The control of this coil group is effected by the relay |22 of control circuit |20. The operation of the relays which control the two Silent coil groups and 2|| is so timed that the audio-frequency circuits are always disabled when other control relays are being operated.

Radio receiver control circuit 120 The control circuit provides voice or carrier operated control of the radio receiver output circuit when it is `rinterlecked with the voice operated control of the radio transmitter control circuit 300 in such av manner that operation of the radio receiver control relay |22 will prevent operation of the radio transmitter, as will be described in detail hereinafter.

Vacuum tube |23 is of the dual function type and comprises a full wave rectier employing the anodes |24 and a three-element section comprising .the grid |25 and anode |26, both sections having a common cathode |21. Space current for the amplifier section is supplied from a direct current supply such as battery4 |28 through a Wheatstone bridge circuit having as three arms thereof the resistors |29, and |3| and as the fourth arm `the cathode-anode path |21-|2|. The operating winding |34 of the relay |22 is connected'across one diagonal of the bridge.

Two potentiometers |32 and |33 are provided for controlling the balance of the bridge, one potentiometer being for Codan operation and the other for Vodas operation. The conditioning of the circuit for either type of operation iscontrolied by the operation of key 2|. When this key is in theleft-hand position as shown the circuit is conditioned for Vodas operation. In this condition, in the absence of arecelved signal in the radio receiver |00. the potentiometer |33 is adjusted to vary the bias on the grid |25 of the tube |23 until the bridge is balanced and no current ilows through the winding |34 of relay |22. Under such conditions the relay |22 will beheld in its normal position by the current in the polarizing winding |39 which current is the normal space current of the tube 324 of the control unit 300 supplied from the battery |40; i. e., the plate current in the absence of a speech or tone input to the control unit 300. When a speech modulated carrier is received in the receiver |00 the speech output current is supplied through the lead |36 and transformer |31 to the full wave rectifier comprising the anode |24, cathode |21 and tube |23. The voltage produced across the resistance |38 by the rectied voice currents is impressed on the grid |25 of tube |23. The effect of this voltage will be to imbalance the bridge and cause current to flow through the winding |34 of the relay 22 to oppose the action of the polarizing winding |39. When the current through the winding |34 becomes sufficient to produce a iiux greater than that produced in the relay by the polarizing winding |22, through which the normal (non-operating) space current of the amplier tube 324 of the control circuit 300 is iiowing, the relay armature will transfer from the left-hand contact to the right-hand contact.

In the operation of the control circuit |20 for the Vodas type of operation sufficient hang-over for the control relay |22 to prevent disabling of the Silent coil group between words of speech is provided by means of the condenser |42 which is charged by incoming speech to the potential developed across the rectiiler load resistance |38. The condensers discharge slowly through the resistor |38 upon completion of a passage of speech to maintain the radio receiver control relay |22 in operated condition for say approximately 150 milliseconds after the last passage of speech.

This operation of the relay |22 performs two functions which are: (l) When the armature leaves its normal (left-hand) contact it breaks the circuit from the high voltage supply |40 of the radio receiver |00 through the receiver disabling relays ||0 and |09 and the control relay 3|3 of the controlr unit 300 to the tube 324. In this manner the radio transmitter is completely disabled until the bridge circuit regains its normal condition when the incoming signals cease; (2) when the armature of the relay |22 reaches its operated contact it connects together the four inner ends of the windings of the transformers of the Silent coil group 2| I. With the transformer windings so connected the audiofrequency output from the radio receiver may pass through the coil group 2|| to the operators control circuit 200.

When the relay |22 is in its normal condition l vare impressed on the transmitter circuit and also during the hang-over time for the transmitter control circuit 300, in the latter case through the operation of the relay` 3|5, current through the winding |39 will be suillcient to hold the relay in its normal positionso that the current produced in the winding |34 by the action of the voice output of the receiver will be insufllcient to operate the relay. After voice currents in the transmitteiceases, the space current of the tube 324 falls, and consequently the polarizing current through the winding |39, to a comparatively small value so that the relay may be operated by the action of the currents in the winding |34.

The hang-over operation produced by relay 3|5 is suchthat the circuit 321 will be closed to ground through the armature of relay 3|5 and resistance 389 for 8 to l0 milliseconds after relays 7'5 lay |22 polarized to disable the receiver during this period. i

For Codan operation of the radio receiver control circuit |20 the negative bias supplied to the grid |25 to cause the operation of the relay |22 -with an incoming carrier, is obtained from the load circuit'oil the detector |01 through the lead I4 'Ihis negative voltage is supplied to the grid |25 through the middle contact of the switch |2| when in its right-hand position. In this position of 'the key |2| the grid |25 is initially biased by the voltage across the potentiometer |32. By the adjustment of this potentiometer the normalgrid bias can be adjusted to apoint where no current ows through the winding |34 of the control relay when no carrier is received by the radio receiver. In a sense this gives the relay |22 the power to discriminate between noise and a desired carrier signal.. o

For Codan operation no hang-over of the relay |22 is provided such as is provided for the Vodas operation by the action of the condenser |22 connected in parallel with resistance |38 as it is assumed that the radio transmitter from which the intermittent carrier receiver is equipped with suitable circuits to produce a carrier lhang-over similar to that provided by the hang-over feature of the control circuit 300.

operators control circuit 200 The operators control circuit comprises two alternative methods of connection, one with the control'unit 240 connected as shown in the drawings, for connection to a four-wire extension or telephone subscribers line 233-234, and the other with the control circuit 250 substituted for the circuit 240 for connection to a two-wire extension or telephone subscribers line 266. These two types of operation will be separately described later.

The dial 580 (Fig. 6) really comprises part of I the operators control unit 200 sothat the operator may select the desired radio frequency channel in the transmitter by the operation of the dial 600. The operation of this dial controls the.

selection mechanism in the 'same manner as the operation of the dial 620 previously described.

48-volt direct current from the rectifier 405 of i to the unltered Litl-volt suppy circuit 202 and is therefore in an operated condition whenever the switch 402 is closed to connect the rectifier circuit to the main power source. In the operated condition of the relay 303 the 48volt circuits in the control unit are connected through the relay armatures to the 48-volt circuits of the transmitter rectifier, the unfiltered sppply 202 being connected throughthe left-hand armature and itsfront contact and the i'lltered supply 20| being connect-ed through the right-hand armature and its front contact. In the unoperated condition of the relay 203, that is when the transmitter-rectifier circuit is not operated, the 48- volt circuits of the control unit are connected to an emergency supplybattery 204 which may be I a battery as indicated, or a portion of a rectied supply for the receiver |00. Thus, whenever the transmitter-rectifier is not connected to the main power source as may be the case during long periods betweenthe use of the radio equipment,

operating voltage from the battery 304 is available for supervision of the extension telephone circuits and for interphone communication between the operators position and any ofthe telephone extensions. i

Radio telephone communication from operators l position 'After the desired radio frequency channel has been dialed, radio communicationv may be carried on from vthe operators position and from the extension telephone in the following manner: When the operators key 220 is thrown to the up or radio position, the operator may. use his telephone set comprising the telephone transmitter or microphone 206 and the telephone receiver 201 for the transmission and reception of radio telephone signals. The operation of the key 220 arranges the circuit for such use as folows:

1. One side of the operators microphone 206 is connected through the `contact 22| to ground. The other side of the microphone is permanently connected to the low impedance winding of the microphone transformer 205 and through the microphone choke coil 208 to the ltered 48-volt supply.

2. Both sides of the high impedance .winding of the microphone transformer 205 are connected through the key arms1222 and 223 to the transmitter volume control attenuator 209 which is used to regulate the speech level supplied to the input circuit of the radio transmitter through the leads 2|0 connected lto the primary winding oi the transformer 208.

3. The operators telephone receiver 201 which is connected to the armatures 2|3 and 2|4 of the relay 2|2 is connected through the back contacts of these armatures, resistors 2|5 and 2|B,`1ower arms ofthe key 220 to the input sideof Silent coil group 2||-. l

With the circuits arranged as just described, voice frequency currents in the high impedance winding of the microphone transformer 205 are applied to the speech input circuit of the transo mitter and will cause operation lof the voice operated carrier control circuit 300 in the transmitterreceiver interlock circuit.

When speech is impressed upon the radio transmitter a side tone signal is furnished to the operators telephone receiver 206. The side tone is developed in the radio transmitter volume indicator circuit as described in a later 'section with the subtitle Monitoring, The volume indicator circuit 2| 1 from the output of the monitoring transformer 4|6 is connected to the radio receiver output circuit throughthe three-way impedance matching pads 2|8 and 2|9.

When no speech is impressed upon the radio transmitter an incoming signal to the radio receiver will reach the operators telephone re-4 ceiver through the pads 2|8 and'2l9.`

Four-wire telephmzcextension The operators control unit 200 vpermits extentype 240. While only one of these umts is shown in' the drawings, it is obvious that additional units with their corresponding keys like 24|, may be similarly connected to permit selective connection of the radio system to any of a group of four-Wire extension telephones.

With the extension key 24| thrown to the upper or operator position and the operators key 220 in the neutral or monitor position, circuits between the subscribers extension and the operators telephone set are completed asfollows:

l. The 48-volt circuit through the winding of relay 2 l2 is completed to ground through the contact 224 of key 220, contact 242 of key 24| causing the relay 2|2 to operate. In the operated condition relay 2|2 completes to ground the 48- volt circuit for the operators microphone through its inner right-hand armature, and transfers the operators telephone receiver from the radio receiver output circuit to one side of the two-way path 230 through its armatures 2l3 and 2 I4. The other side of the path 230 is connected to the output winding of the microphone transformer (not shown) is removed from its switch-hook the leads 234 are connected together through the extension microphone element and the primary winding of the extension telephone induction coil. Current from the iiltered 48-volt source will then flow from lead 238 through winding 236 of relay 235 through the microphone of the subscribers set returning to ground through the winding 231 of relay 235. Speech impressed upon the subscribers microphone superimposes an alternating current upon the direct microphone current and speech voltages appear across the windings of relay 235. 'Ihe subscribers microphone circuit 234 will also be connected through the upper arms of the key 24|, blocking condensers 26| and 262, through the resistors 23| and 232 and to the output side of the pad 230 and consequently through the front contacts and armatures 2I3 and 2|4 of relay 2|2 in the operators receiver 201. The resistors 23| and 232 furnish a connection between the subscribers talking circuit 234 and the subscribers listening circuit 233 thus furnishing side tone to the subscriber.

The circuit just described completes the connection for two-way interphone connection between the subscriber and the operator.

The operator permits the subscriber to communicate over the radio circuit from the fourwire extension telephone connected to the circuits 233 and 234 by throwing the extension key 24| to the lower or radio position. In this position of the key the following circuit arrangement results:

The 48volt circuit through the winding of relay 2|2 to ground is broken at the arm 242 of key 24| allowing the operators telephone receiver to be reconnected to the radio receiver output circuit through the normally closed contacts of the operators key 223, that is, with the key 220 in the neutral position.

The output of the radio receiver after passing through the Silent coil group 2|I is connected through the arms 241 and 248 of the key 24| to the subscribers telephone receiver circuit 233.

'I'he speech circuits from the subscribers telephone transmitter circuit 234 are applied through the arm 249 of the key 24| and the blocking condensers 263 and 264 to the transmitter volume attenuator 209 and thence to the speech input circuit of the radio transmitter.

For supervision of the four-wire telephone extension the key 24| is in its neutral position. When the subscribers telephone set is removed from the switch-hook a direct current path is provided between the leads 234, as previously described. Current may then flow from the filtered A1li-volt source to the subscribers microphone circuit and through the windings of the supervisory relay 235 causing the relay 235 to operate. When the relay 235 operates, the grounded armature provides a path for current from the 1B-volt circuit from ground, armature of relay 235, contacts 245l and 246 of the key 24| in its neutral position, supervisory lamp 265 to the positive 48- volt terminal, causing the lamp 265 to light indicating that the subscriber is calling.

When the operator answers the incoming call by throwing the key 24| to theupper position the indicator lamp circuit will be broken for as long as the key is in either upper or lower position and the extension set remains 01T the switchhook. When the extension set is replaced on the switch-hook after completion of the call, the 48- volt circuit through the relay 35 is broken and the relay armature is released falling against its back contact. If the key 24| is then in the lower or radio position the armature of relay 235 will again supply ground to the indicator lamp indicating to the operator that the radio call has been completed.

Two-wire telephone extension For operating the radio system with a subscribers two-wire extension telephone circuit such as the usual commercial type telephone system, the unit 250 is substituted for the unit 240, the connections being made to the letter terminals as indicated. In this system the conventional commercial type of two-wire subscribers telephone set (not shown) terminates in the line 266. With this circuit the operation of the key 252 permits interphone communication between the operator and subscriber and also radio .telephone communication from the remote subscribers stations.

With the operators key 220 in the neutral position the operator may answer an incoming cali from the two-wire extension by throwing the extension key 252 to the upper position arranging the circuit for interphone communication as follows:

1. Ground is connected to the winding of relay 2|2 through the arm 224 of switch 220, terminal I-I, upper right-hand arm of key 252 to ground, the operator being furnished a side tone and speech from his microphone appearing at the terminals D and G in a similar manner as in connection with the four-wire circuit.

2. The speech circuit terminating in the terminals D and G is connected through the contacts 253 of key 252 to the arms 261 and 263 of the three-way impedance matching pads allowing the operators speech currents to go over the line 266 to the subscribers set.

3. Additional contacts on the key 252 connect the retard coil 269 between the same terminals of the resistors 261 and 268 providing a low resistance path for direct current across the line 266. This direct current path is to complete supervisory circuits in commercial or private branch Y 9,101,668 exchange telephone oinceJ eduipinent to which the by the two-wire extension supervisory relay" 21| line 266 maybeconnected. will again operate upon completion of a call.

4. 4Speech` currents originating inthe subscrib- -er's set and coming over theline 266 iilow through is required in the operators control circuit as such l side tone circuit is furnished by the circuit o! the `subscribers telephone set itself.

t nected to the radio equipment by closing lthe key In that f -key 252 mmaucuon cou-m thus providing a- ClA the neutral position. y

blocking condensers 263 and f264 The two-wire telephone extension may be con- 252 to its lower or radio position. position of the key the'f.. extension subscrlbers circuit is completed i'or radio telephone communication in the followingLriiar'iner:

I. The two lower left-hand closed contacts` of the key 262 connect the extension line 266 through the resistors21i and 212 oi the three-way p ad to the terminals A and'B and thence through the input to the radio transmitter. v 2. Theoutput oi the radio receiver' after passing through the Silent coilgroup 230 terminates in the :terminals J and Kfand-is 'their'connected through the two lower right-hand closed contacts oi? the key 262, resistors261 and 266 of the threeway pad to the subscribers extension line 266. Incoming signalstol the radio receiver may therefore go over the two-wire line 266 tothe sub.;

scriber. K

3. The resistors 261 and 266 oi the .three-way pad are also connected through contacts of the direct current path between the conductors ofthe extension line 266 for holding Vup supervisory relays in an associated telephone exchange equipvolt circuit oi the loperator-'s control equipment l at the terminal I and to the relay front or holding contact. The armature of the relay 21| is connected to ground through a series connection including one pair of `contacts on each side of the key 252. Thus, when a ringing current is supplied over the line 266, the lrelay 21| will be operated and locked up through its holding circuit in the `operated position byb the current from the iS-voit source through the holding winding 213 for as. long a time as the key 252 remains in The front contact ofthe relay 21| is also Vconnected to the supervisory lamp 215 so that when the relay 21| is operated a circuit from the 48- volt supply ai; terminal I is provided through the lamp 215.

When the incoming call is answered by closingthe keyV 252 to its upper or iope'rator" position, the ground return circuit from the supervisory l relay holding winding is opened allowing the relay armature to fall back.l At the same time ground' is also removed from the indicator lamp 215 extinguishing` the lamp. I

No provision is made in the control unit wheref vthrough tol the speech However. the operator will knowJ when a radio call has been completed by\ monitoring on the .radio circuit. -I

Monitoring 'With the operators key 220 in the neutralA or ."monitpr" position, the operator may listen tor incoming calls in the' output oi the-radio re-y ceiver. In this condition the operators telephone receiver is also connected' to the volume indicator circuit of the radio transmittery through the connection 2I1 permitting the'joperator to monitor speech both to and from' a subscriber.

In the neutral` position .of the operators key 226, the operators telephone receiver is connected through closed contacts on the key and t backncontactson relay `2| 2 Ato the input side o! the Silent-.coil group 2| i. ."I'helinput side of this coil group 2|'| connects both' tothe audioirequency output circuito! the radio receiver |00 and to the'radio transmitter monitoring circuit through the three-way pads 2| 6 and v2|0. l

vIn this manner the operator may hear both sides of the radio conversation when the radio equipment is connected to .a subscriber. When speech froma subscriber is impressed upon the radio transmitteri the Silent coil group 2li being disabled through vthe action of the control relay |22, the subscribers speech in the monitoring circuit is prevented from getting back to the subscriber by the Silent coil group 2| i.

With the operators key in the lower position `the operator jis permitted to hear the received signal exactly as it is-heard by the subscriber.

In this position .of the key the operator-fs tele'- phone receiver4 is transferred to the output side of the Silent coil group 2| i enabling him to detect and. correct am? false operationI of the radio receiver control relay |22'.I

Volume indicator The volume lindicator meter 214 may be used to indicate the speech or tone levelslboth into -the' radio transmitter and out of the radio receiver. With the volume indicator key 216 in the lower position, as shown inthe drawings, the indicator is connected to the line 2|1 which connects the secondary of the monitoring transformer 4|6 of the transmitter, the primary winding of this transformer being connected in the plate return circuit of the radio transmitter power ampliner tube as previously described. The nature oi' the circuit is such that the potential across the volumeindicator meter 216 is a func-n tion of .the speech or tone components oi the power amplifier plate current. I With the volume indicator key- 216 in the upper position,l the volume indicator meter 214 is connected directly across the output of the radio receiver |00. the operator may adjust the level of the received speech always to the same predetermined level most satisfactory to the subscriber.

The potentiometer 211 is provided for regulat- A ing the sensitivity of. the voice operated radio transmitter controlunit 300 when the sensitivity control switch 36| is in the left-hand position. The purpose of this potentiometer 211 is to select the maximum `permissible sensitivity ,of the radio transmitter voice operated control unit un- "der varying conditions of room' noise, speakers voice level-and line noises of any nature.- .v

The transmitter sensitivity potentiometer 211 In that position oi the key 216 regulates the bias potential applied to the grid of the second amplifier tube 824 thereby controlling the magnitude of the plate current supplied to that tube through the operating winding on the transmitter carrier control relay 818.

. Radio telegraph communication The system may be used for radio telegraph transmission by supplying a tone to the radio transmitter speech input circuit by the operation of the telegraph key 218. The oscillator 288 which will supply a tone say of approximately 800 cycles for transmission of telegraph signals in the following manner:

The tube 28| of the oscillator receives niament heating current and plate supply from the unfiltered 48volt circuit when the tone control key 282 is closed. With the oscillator made ready for use by closing the key 282 the operator may condition the circuit for either M. C. W. or C. W. transmission by closing the key 288 to either the upper or lower position, respectively. Thus,

, the key 282 may remain closed to energize the tube 28| during the radio telephone transmission period without interfering with the transmission of telephone signals provided the key 288 is in the neutral position.

With key 288 in the upper or M. C. W. position one terminal of the output winding 288 of the oscillator transformer is connected through the left-hand contact oi the key 288 to the telegraph key 218 and the other side of the winding 284 is connected through the right-hand contact of key 288 to the other side of the input circuit 2I0 to the radio transmitter. At the same time +48-volt battery is applied through the righthand contact of key 288, connection 288 through the winding of the relay 8I8 of the control unit 308. Relay 8|! is therefore operated for as long a time as the key 288 is in the upper or ll. C. W. position and its upper armature short-circuits the winding of relay 8I8 which if allowed to operate would hold open the ground circuit to the plate of the radio frequency oscillator tube I8 and maintain the oscillator in operated condition between tone impulses to the speech input circuit. With the transmitter hang-over thus removed, that is, by the snorting of the winding of the relay 8M, tone may be supplied to the speech input circuit of the transmitter by pressing the telegraph key 218 to cause the carrier control relay 8l8 to operate each time the key is pressed and falling back to the unoperated condition each time the key is released. The impressed tone pulses are allowed to pass through the audio-amplifier comprising' the tubes 808 and 3I0 and thus to modulate the interrupted carrier wave.

With the key 288 thrown to the lower or C. W. position the circuit is conditioned for the transmission of C. W. telegraph signals. Tone is again supplied through the telegraph key 218 to the radio transmission speech input circuit when the telegraph key is pressed. In this position, however, the key 288 connects +48 volts through the connection 288 to the ungrounded side of the winding of the relay 8|! causing it to become operated in which condition it performs vtwo functions, namely: (1) the input to the second audio-frequency ampliiler tube 8I8 is shorted through the upper armature of the relay 8|2 preventing the impressed tone pulses from being ampliiled and applied to the carrier of the radio transmitter; (2) the outer lower armature of the relay 8I2 short-circuits the winding of hangover relay 8I8 removing the carrier hang-over between tone impulses applied to the speech inputcircuitasinthecaseforltaw. transmission.

What is claimed is:

1. A two-way radio communication system comprising a radio transmitter. a radio receiver. an electric discharge device having an input circuit connected to the signal input to the radio transmitter, a iirst relay having a winding connected in the space current path of said device and operated by the increased space current due to signal waves in the input, means responsive to the operation of said relay for enabling the transmitter for the generation and transmission of a carrier wave, a second relay responsive to the operation of the first relay for establishing an auxiliary circuit for enabling the radio transmitter. time controlled means for maintaining said second relay operated for a period after the release of said nrst relay suihciently long to prevent undesired interruption of the carrier between syllables or words spoken in rapid succession, a third relay operated simultaneously with the first relay for disabling the radio receiver, and a fourth relay operated by the nrst relay for providing an auxiliary operating circuit for said third relay, and time controlled means for maintaining said fourth relay Operated for an interval of the order of 8 to 10 milliseconds after the release of the second relay.

`il. In a two-way radio communication system, a radio transmitter, a radio receiver. means for normally maintaining said transmitter in an inoperative condition and said receiver in an operative condition. an electric discharge device having an input circuit connected to the signal input circuit of said transmitter, a source of space current for said device, a plurality of relays having windings connected in series with said source in the space current path oi said device and operated on the increased space current of said device due to signal waves in said input circui means responsivev to the operation of one of said relays for rendering said transmitter operative, means responsive to the operation of another of said relays for rendering said receiver inoperative, a first and a second hang-over relay, means responsive to the operation of said one relay for operating said hang-over relays, means responsive to the operation of said ilrst hang-over relay forestablishing an auxiliary circuit arrangement for maintaining said transmitter in an operative condition irrespective of the condition of said one relay, means responsive to the operation of said second hang-over relay for establishing' a circuit for maintaining said other relay operated irrespective of the condition of the space current path of said device, time controlled means for maintaining said rst hang-over relay operated for a period after the release of said one relay sufficiently long to prevent undesired interruption of the transmission by said transmitter between syllables or words spoken in rapid succession, time controlled means for maintaining said second hang-over relay operated for a few milliseconds after the release of said ilrst hang-over relay, and means responsive to waves received by said receiver for opening the space current circuit of said device.

3. In a two-way radio communication system,

a radio transmitterl a radio receiver, means for normally maintaining' said transmitter in an inoperative condition and said receiver in an operative condition, an electric discharge device havcircuit o! said radio transmitter, a sourcel of spacel current for said device, a plurality o! relays connected in series with said source in the space current path o! said device and operated on the increased space current ot said device due to the signal waves in said input circuit, means responsive -to the operation of one of said relays for rendering said transmitter operative, means responsive to the operation of yanother of said relays for rendering said receiver inoperative, a

1 hang-over relay connected to be operated by the operation of said one relay. means responsive to the operation of said other relay for establishing an auxiliary circuit arrangement for maintaining `said transmitter in an operative condition irrespective of the condition of said one relay, and

time controlled means for maintaining said hang-over relay operated for a period aiterthe release of said one relay suillciently long to preoperative condition and said receiver in an operative` condition, an electric discharge device having an input circuit connected to the signal input circuit of said transmitten'a source of space current for said device, a radio transmitter controlling relay, 'a group of radio receiver controlling relays, connections for including the windings of said transmitter controlling relay and said receiver controlling relays in series with said source in the space current path of said device so that all of said relays are operated on the increased space current of said device due to the signal waves in said' input circuit, means responsive to the operation of said radio transmitter controlling relay for rendering said transmitter operative, means responsive to the operation of said radio receiver controlling relays for rendering both the radio frequencycircuit and the audiofrequency circuit of said radioreceiver inoperative, a rst and a second hang-over relay, means responsive t0 the operation of said transmitter controlling relay for operating said hang-over relays, means responsive to the operation oi' said first hang-over relay for establishing auxiliary circuit arrangements for maintaining said transvmittel' in an operative condition irrespective of the condition of said transmitter 'controlling yrelay, means responsive to the operation of said second hang-over relay for establishing a circuit for maintaining said radio receiver controlling relay operated irrespective of thecondition of the space current path of said device, time controlled means for maintaining saidrst hangover relay operated for a period after the release of said one relay suii'iciently long to prevent undesired interruption of the operative condition of ing an input circuit connected to the signal input t3 the space current circuit of said discharge device.-

5. Inl a/.two-way radio transmission system a.4

radio receiver, a radio transmitter employing electric Adischarge devices, a source of power for energizing said devices, means responsive to the signal wave input of said transmitter tor controlling an operative condition of said transmitter to render said transmitter operative for transmission of radio waves in the presence oi a signal wave input and to prevent the transmission of radio waves in the absence oi a signal wave input, time controlled means operative a predetermined time after the initiation of its operation to interrupt the. supply of power from said source to said discharge devices, and means responsive to the cessation of signal input for initiating the operation of said time controlled means.

6. In a two-way radio transmission system, a radio receiver, a radio transmitter employing electric discharge devices, a source of cathode heating current and a source of space current for said devices, means responsive to the signal input to said transmitter for controlling an operative condition of said transmitter to render said transmitter operative yfor the transmission of 4 radio waves in the presence of a signal wave input and to prevent the transmission of radio waves in the absence of a signal wave input, time controlled `means operative a predetermined time after the initiation o! its operation to interrupt the 'supply ot space lcurrent from said source Vto said discharge device, means responsive to the cessation of the signal wave input for initiating the operation of said time controlled means,y and a second time controlled means operative a predetermined time after the initiation of its operation to interrupt the supply of cathode heating current to said discharge devices, and means responsive to the ilnal operation of the first time controlled means for initiating the operation of said second time controlled means.

7. In` a two-way radio communication system, a radio receiver, a radio transmitter of the vacuum tube type, a power supply for said radio transmitter," a control circuit comprising a vacuum tube, a relay for controlling an operative condition of said radio transmitter, a second relay for controlling an operative condition of said radio receiver, and a series circuit including the windings of said relays and the anode-cathode circuit of said vacuum tube, means responsive to the signals to be transmitted for rendering said vacuum tube conductive whereby said relays operate to enable said transmitter and disable said receiver, time controlled meansoperative la predetermined time after the initiation of its operation to interrupt the supplyof power to said radio transmitter, `and means responsive to the operation of said rst relay for initiating the operation of said time controlled means.

8. In a two-way radio transmission system, according to claim 7, a second time controlled vmeans operative a predetermined time afterthe initiation of its operation to interrupt the supply of cathode heating current to the vacuum tubes of said radio transmitter, and means responsive to the naloperation of the first-mentioned time controlled means for initiating the operation oi' said second time controlled means.

9. In a two-way radio communication system,l

a radio receiver, a radio transmitter, a plurality of sets oi' tuning units for said transmitter, each set being adapted for tuning said transmitter for transmitting at a different frequency, a selec- I tor switch control mechanism -for selectively connecting said sets of tuning units in circuit in said transmitter, means operated by said selector switch control mechanism for connecting high voltage'power to said transmitter, relay means operative in a normal condition for renderingsaid transmitter inoperative and in an operative position for rendering said transmitter operative for the transmission oi radio waves, time controlled means operative a predetermined time after the initiation oi its operation to release said selector switch control mechanism whereby the high voltage power supply and the sets of tuning units are disconnected from said transmitter, and means operated by the operation oi said. selector switch control mechanism or by the normal condition oi said relay means for initiating the operation -of said time controlled l0. In a two-way radio communication system, a radio receiver, a radio transmitter, a plurality oi sets of tuning units ior said transmitter, each set being adapted ror tuning said transmitter ior transmitting at a dierent frequency, a selector switch control mechanism for selectively connecting said sets oi? tuning umts in circuit in said transmitter, means operated by said selector switch control mechanism for connecting high voltage power to said transmitter, means tor normally maintaining said transmitter in an inoperative condition and said receiver in an operative condition, an electron dischargedevice having an input circuit connected to the signal input circuit of said transmitter, a source of space current ior said device, a plurality of relays having windings connected in series with said source and the space current. path of said device and operated on the increased space current of said device due to signal waves in said input circuit, means responsive to the operation of one of said relays/for rendering said transmitter operative, means responsive to the operation ot another o! said relays ior rendering said receiver inoperative, a ilrst and a. second hang-over relay, means responsive to the operation oi said one relay for operating said hang-over relay, means responsive to the operation of said nrst hang-over relay for establishing an auxiliary circuit arrangement for maintaining said transmitter in an operative condition irrespective of the condition of said one relay, means responsive to the operation of said second hang-over relay for establishing a circuit for maintaining said other relay operated irrespective oi the condition of the space current path of said device, time controlled means for maintaining said rst hang-over relay operated for a period after the release of said one relay suiilciently long to prevent undesired interruptions oi the transmission oi said transmitter between syllables or words spoken in rapid succession. time controlled means for maintaining said second hang-over relay operated for a i'ew milliseconds after the release of said ilrst hang-over relay,

means responsive to waves received by said receiver for opening the space current circuit oi said device, time controlled means operative a predetermined time after the initiation ot its operation to release said selector switch control mechanism whereby the high voltage power supply and the sets of tuning units are disconnected from said transmitter, and means operated by the meansior normally maintaining said transmitter inoperative for initiating the operation of the last-mentioned time controlled means.

1l. In a two-way radio communication system, a radio receiver, a radio transmitter employing a plurality of vacuum tubes. a plurality of sets of tuning units for said transmitter, each set being adapted for tuning said transmitter for transmitting at a different frequency. a source for supplying space current to said vacuum tubes.

a selector switch control mechanism for selectively connecting said sets oi tuning units in circuit in said transmitter, means operated by said selector switch control mechanism ior completing the circuit from vsaid source for supplying space current to said vacuum tubes. a controlvacuum tube having an input circuit connected to the signal input circuit of said trans mitter, means for deriving space current from. said source ior said control vacuum tube including the means operated by said selector switch control mechanism for completing the circuit from said source to the vacuum tubes oi. said transmitter, a plurality' of relays having windings connected in series with said source in the space current path oi' said control vacuum tube and operated on the increasein space current oi said control vacuum tube due to the signal waves in said input circuit, a control circuit including contacts of one oi.' said relays, an inductance 'coil and a resistor for grounding the anode oi' one oi the vacuum tubes oi said radio trans,

mitter to render said transmitter inoperative when said one relay is in a normal condition, means responsive to the operation oi another oil said relays for rendering said receiver inoperative, a ilrst and a second hang-over relay, said ilrst hang-over relay having contacts in seriesin said circuit for grounding the anode of one of the vacuum tubes ot said transmitter when said ilrst hang-over relay is in a normal position, means responsive to the operation 'of said one relay for operating said hang-over relays whereby when said ilrst hang-over relay is operated said circuit for grounding the anode oi one of the vacuum tubes oi said transmitterls open to render said transmitter operative, means responsive to the operation oi said second hangover relay for establishing a circuit for maintaining said other relay operated irrespective of the condition of the space current path of said control vacuum tube, time controlled means for maintaining sa'id ilrst hang-over relay operated for a period after the release oi' said one relay sumciently long to prevent Vundesired interruption oi the operative condition of said transmitter between syllables or words spoken in rapid succession, time controlled means i'or maintaining said second hang-over relay operated for a few milliseconds after the release of said rst hang-over relay, means responsive to the waves received by saidreceiver for opening the space current circuit of said control vacuum tube, relay means having a winding connected in said control circuit for grounding the anode oi one of the vacuum tubes oi said transmitter and arranged to be operated a predetermined time after its initial energization, means responsive to the operation of said last-mentioned relay means to release said selector switch control mechanism whereby the power supply circuit for the space current of the vacuum tubes of said radio transmitter is interruptedand the set of tuning units is disconnected from the transmitter.

l2. In a radio transmitter employing an elecl plying space current to said device, means ior

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