US1484087A - Radio broadcasting equipment - Google Patents

Description

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1,484,087 F. M. RYAN RADIO BROADCASTING EQUIPMENT Filed Aug. 14. 1922 3 Sheets-Sheet 5 lnven/an Frana: M I? an A/fy HRMIHRE i Patented Feb. 19, 1924.

UNITED STATES PATENT OFFICE.

FRANCIS M. RYAN, OF EAST ORANGE, NEW JERSEY, ASSIG-NOR TO WESTERN ELEC- TRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF'NEW YORK.

RADIO BROADCASTING EQUIPMENT.

Application filed August 14, 1922. Serial No. 581,613.

To all 10 ham it may concern:

Be it known that I, FnANoIs M. RYAN, a citizen of the United States, residing at East Orange, in the county of Essex, State of New Jersey, have invented certain new and useful Improvements in Radio Broadcasting Equipment, of which the following is a full, clear, concise, and exact description.

This invention relates to radio telephone broadcasting systems and method of operating the same and more particularly to control and signal circuits for such systems.

In radio telephone broadcasting systems it is customary and practically necessary to have the radio apparatus located at a distance from the telephone transmitter used for translating sound waves into audio fre quency electric waves. For this reason, th radio apparatus is usually located in one room which may be designated as the radio room; while the telephone transmitter is located in a separate room which may be called the studio or concert room. 'Some means of intercommunication between the studio and radio room attendants must therefore be provided.

An object of this invention is to provide a simple yet effective means of intercommunication for this purpose. Another object of the invention is to provide a control system partially under the control of the radio room attendant and partially under the control of the studio attendant. Another object is to provide a control system, the several parts of which are so interlocked that they will all function in proper sequence. Still another object is the provision of indicating devices to automatically indicate various circuit conditions.

In one embodiment of the'invention a radio transmitter adapted to modulate radio frequency waves in accordance with audio frequency waves is connected to a radiating system or antenna by means of an electrically operated antenna switch. Audio frequency waves supplied by a telephone transmitter are amplified in an audio frequency amplifier and impressed upon the radio transmitter. The connection of the audio frequency amplifier to the radio transmitter is controlled by a relay. One telephone transmitter is located in the studio and another in the radio room, the connection of the one or the other to the audio frequency amplifier being controlled by a manually operated switch in the radio room. A second manually operated switch in the radio room controls the antenna switch, the amplifier connecting relay and'a signal or supervisory lamp in the studio designated as radio. A manually operated switch in the studio also controls the amplifier connecting relay, a signal or supervisory lamp in the radio room designated as studio broadcast and a second lamp in the studio designated as broadcast. Another lamp in the radio room designated radio broadcast is under the control of the transmitter switch. A monitoring loud speaking receiver may be connected either to the audio frequency input circuit of the radio transmitter or toa monitoring radio receiver circuit, but only at such times as the telephone transmitter in the radio room is not connected to the audio frequency amplifier.

The novel features which are considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation together with further objects and advantages thereof will best be understood by reference to the following description taken in connection with the accompanying drawings in which Fig. l and Fig. 2 taken together illustrate one embodiment of the invention, while Fig. 3 illustrates a modification of the control circuits of Figs. 1 and 2.

Referring now to- Fig. 1, the blocks A and B enclosed by dot and dash lines represent respectively apparatus located in a studio and a multi-stage audio frequency amplifier. Referring to Fig. 2, blocks C, D

and E also enclosed by dot and dash lines represent, respectively, the radio transmitter whereby radio frequency waves may be modulated in accordance with audio frequency waves, an electrically operated antenna switch for transferring the antenna from the receive to the transmit condition and vice versa, and control and signal apparatus. The apparatus shown within blocks B, D, and E are ordinarily located in a room which may be designated as the radio room. The apparatus shown within block C with the exception of the sources of filament heating and plate current is also ordinarily located in the radio room.

A telephone transmitter 4 in the studio A comprising two carbon buttons 5 and 6, one on each side of a vibrating diaphragm 7, is connected to the input circuit of the audio frequency amplifier B through the lower contacts of transmitter switch 8. A similar transmitter 9 in the radio room shown within block E may be connected to the input circuit of the amplifier B through the upper contacts of switch 8.

The amplifier located on the amplifier panel B comprises three electron discharge devices 10, 11, and 12 connected in tandem. Each of these devices preferably has an ordinary electron emitting cathode or filament, an anode or plate and an impedance controlling element or grid. The filaments of devices 10 and 11 are connected in series and heated by current from battery 13 through a circuit which may be traced from the positive terminals of battery 13, which terminal is also connected to ground, through the filament of device 11, resistance 14, filament of device 10, resistance 15, choke coil 16, and filament controlling rheostat 17 to the negative terminal of battery 13. Filament of clevice 12 is likewise heated by current from battery 13 through a circuit which may be traced from the positive terminal of battery 13 through the filament of device 12, choke coil 18, filament cont-rolling rheostat 19 to the negative terminal of battery 13.

Direct current for the transmitters 4 and 9 is also supplied by battery 13 over a circuit which may be traced from the positive terminal of battery 13 to the left-hand terminal of resistance 20, conductor 21, to the diaphragms and carbon buttons of transmitters 4 and 9, lower or upper left-hand and middle blades of transmitter switch 8, depending upon the position of switch 8, conductors 22 and 23, opposite terminals of input transformer 24 and right-hand terminal of resistance 20, switch 25, choke coil 26, resistance 27 to the negative terminal of battery 13. Resistances 20 and 27 with choke coil 26 serve as a potentiometer to control the current to the transmitters 4 and 9.

Space current for devices 10, 11 and 12 is supplied by battery 28 through choke coils 29, 30 and 31 connected in parallel by way of terminals I and J. In case it is desired to use a higher plate potential for device 12 than for devices 10 and 11 resistance 32 is former 24. The amplitude of the impressed waves is determined by the position of switch 34 in conjunction with resistance 35. The output circuit of device 10 is coupled to the input circuit of device 11 through condenser 36 and potentiometer 37. The output circuit of device 11 is coupled to the input circuit of device 12 by means of condenser 38 and potentiometer 39. The output terminals of device 12 are coupled to the output conductors 40 and 41 of the audiofrequency amplifier by condenser 42, output transformer 43 and front contacts of relay 44 (normally open). Negative grid polarizing potential for devices 10 and 11 is furnished by the potential drop across resistances 15 and 14 respectively due to the flow of filament current through those resistances. Negative grid potential for device 12 is supplied by battery 45.

The radio transmitting apparatus at C comprises an oscillatorO,a variable impedance device M and a thermionic amplifier L. The oscillator 0 includes two electron discharge devices 50, connected in parallel and each having the usual cathode, anode and impedance control element or grid. The alternating current output circuit of the devices 50 may be traced from their anodes or plates by way of choke coils 51, 51, condenser 52 and primary winding 53 in parallel, and condenser 54 to the cathodes or filaments. Primary winding 53 is inductively coupled to secondary winding 55 in cluded serially in the circuit of conductor 56 which extends to the antenna 57. The primary winding 58 also included serially in the antenna circuit is inductively coupled to the secondary winding 59 and serves to feed back oscillations from the antenna circuit to the alternating current input circuit of devices 50 which includes winding 59 and capacity element 60 in series. The inductometer winding 61 which is mounted rotatably with respect to the other windings of the antenna circuit provides variation in the tuning of the antenna 57 which serves as a frequency determining circuit for the os cillator O. The variable condenser 52 serves to so change the constants of the interior circuit as to prevent oscillations therein. This interior circuit comprises winding 59, condenser 60, condenser 54, elements 52 and 53 in parallel and the inherent capacity between the anodes and control elements. Condenser 52 therefore serves to prevent the absorption of power by interior oscillations. It further serves to improve the power factor of the plate current, in a measure compensating for the leakage reactance of the winding 53.

Modulation is accomplished by means of the constant current system fully disclosed at page 360, Proceedings of American Institute of Electrical Engineers, volume 38,

No. 3. The variable impedance device M comprises two electron discharge devices 62 connected in parallel. A generator GB supplies space current to devices 50 and 62 in parallel over a path including constant current choke 63, inductance 64 and switch 109. From the negative terminal of generator GB the space current path may be traced by way of the left-hand blade of switch 109, resistance 67 and resistance 68 to the cathodes of devices 50 and 62. Connected in shunt across the space current circuit are capacity elements 69 which in conjunction with series inductance 64 serve to prevent commutator ripples and other fluctuations in the voltage of source GB- from affecting the space current, and also serve to prevent high frequency oscillations from being impressed upon the generator GB through the space current circuit. In series with the anodes of devices 62 are high frequency choke coils 87. The choke coils 51, 51 and 87, 87 prevent parasitic oscillations in the devices with which they are associated at a frequency above the generated radio frequency. Filament heating current is supplied by generator GA through switch 110.

The input circuit of thermionic amplifier L is coupled by transformer 7 3 to the audiofrequency conductors 40 and 41. The secondary winding of transformer 73 is shunted by resistance 74 to improve the impedance characteristic of the transformer 73 in well-known manner. Amplifier L is supplied with cathode heating current from source GA and with space current by source GB over a path identical with that of devices 50 and 62 except that instead of passing through the constant current choke 63, the space current for the amplifier traverses a resistance 75 to reduce the effective voltage impressed across the electrodes of the amplifier. Resistance 75 is shunted by a capacity element 76 to reduce the impedance of the output circuit of the amplifier for the amplified audio-frequency current. The transformer 77 couples the output circuit of amplifier L with the input circuit of variable impedance device M. A resistance 78 of small magnitude with respect to the internal input impedance of device 62 is included in shunt with the secondary winding of transformer 77 to stabilize the impedance connected to this winding. The radio frequency choke 79 which freely passes low frequency signal current serves to prevent radio frequency oscillations from being impressed upon and dissipated in the circuits of the variable impedance device M and the space current generator GB. The cathode of each electron discharge device is equipped with an individual regulating resistance 80 for varying the heating current.

The input circuit of amplifier L may be traced from the impedance control element of the amplifier through the secondary Winding of transformer 73 to the lower terminal of resistance 67 and thence through this resistance and the resistance 68 to the oathode. Since space current passes through resistances 67 and 68 there will be a potential drop between the cathode and the lower terminal of resistance 67, and the control element or grid of the amplifier L will accordingly be maintained at a potential negative with respect to that of its cathode. The input circuit of discharge devices 62 is also connected to the lower terminal of resistance 67 and their impedance control elements are accordingly maintained at a potential also negative with respect to the cathodes. The grid leak path of the oscillator includes a resistance element 81 connected to the upper terminal of resistance 67 and the control elements or grids of the oscillator O are maintained at a less negative potential determined by the potential drop across resistance 68 in consequence of the space current flowing therethrough. The grids of the amplifier L, variable impedance -device M and oscillator O are accordingly each maintained at such negative potentials with respect to their individual cathodes as to reduce their respective space currents to extremely small values. Oscillations are not produced under these conditions. A time limit relay 82 is connected across the terminals of generator GA. This relay, when energized, closes its normally open contacts 83 to short-circuit resistance 68, provided antenna switch is in the transmit position and the normally open contacts 84 are closed, as will be described hereinafter. As soon as resistance 68 is shortcircuited the grids of the various discharge devices become less negative and permit more space current to flow, thus rendering each of the devices operative and causing radio frequency oscillations to be produced in the antenna. This action is further increased by the reduction of the external resistance in the space current circuit when resistance 68 is short-circuited, in effect, increasing the effective space current voltage. In order to prevent surges in the space current circuit in consequence of the opening or closing of contacts 83, a path including a resistance 85 and a capacity element 86 in series therewith is shunted across the terminals of resistance 68.

Ammeters 200 and 201 are conveniently located to measure the space current of the variable impedance device M and oscillator 0 respectively. The unidirectional grid current of the oscillator O and the antenna current are indicated by ammeters 203 and 202 respectively.

The antenna 57 is normally connected to a radio receiver indicated by block 87 and erartsin telephone receivers 88 located near the control apparatus at E through the upper closed contacts 89 and 90 of the antenna switch D. In order to connect the antenna 57 with the radio transmit-ting apparatus by way of conductor 56, the switch 91 is closed. The closure of switch 91 causes current to flow through relay 92 from battery 13 to close the normally open front contacts of relay 92. The closure of the front contact of relay 92 causes current from the low volt age generator GA to flow through the windings 93 of the antenna. relay in parallel. The energization of windings 93 of the antenna relay opens the upper contacts 89 and 90 and closes the lower contacts 94 and 95. At the same time normally open contact 84 is closed in order to complete the circuit for short-circuiting resistance 68 upon the closure of contacts 83 of time limit relay 82 for the purpose hereinbefore described. A resistance 96 is connected in series with the parallel connection of windings 93 and when the short-circuit thereabout is removed by the opening of contact 97 the holding current through windings 93 is reduced.

In order that the radio operator may monitor the audio frequency waves which are impressed upon the input circuit of the radio transmitting apparatus through transformer 73 the loud speaking receiver 98 is bridged across the input conductors 40 and 41. This receiven may be disconnected in any suitable manner as circumstances may require.

The closure of switch 91 also causes lamp 100 in the studio A to be lighted from the battery 13 and partially prepares a circuit for the energization of relay 44 from the same battery. If the transmitter switch 8 is in the lower closed position, the energization circuit for relay 44 may be traced from the negative terminal of batter 13, switch 91, winding of relay 44, right-liand lower closed contact of switch 8, radio broadcast lamp 101, winding of relay 102, switch 103 (it closed) to the positive grounded terminal of battery 13. If the transmitter switch 8 is in its upper closed position, the energization circuit for relay 44 instead of extending through lamp 101, relay 102, the switch 103 extends through the upper right-hand closed contact of switch 8, resistance 104, switch 105, through ground to the positive terminal of battery 13. It is thus seen that audiofrequency waves from the output circuit of amplifier B can only be impressed upon the audio-frequency input circuit of radio transmitter C through conductors 40 and 41, after the switch 91 has been closed and the radio transmitting apparatus is consequently functioning and connected to the antenna 57. If the transmitter switch 8 is in the lower position, thereby connecting the studio transmitter 4 to the input circuit of the amplifier B, the studio attendant has control of relay 44 at switch 103. When switch 103 is closed, thereby energizing relay 44, the radio attendant is notified by the lighting of lamp 101 and relay 102 is energized to light the broadcast lamp 106 in the studio by current from battery 13 through the front contact of relay 102. A buzzer 107 controlled by push button 108 is operated by current from battery 13.

The method of operation is as follows:

Preparatory to operating the system the radio attendant closes radio transmitter filament heating circuit switch 110, radio transmitter space current switch 109, audio frequency transmitter switch 25, the filament heating circuits of amplifier B at variable resistances 17 and 19, which for maximum value of resistance may be open circuited, and the space current circuits of amplifier B at terminals H, I, J and K. Upon the closure of switches 110 and 109 the generator GA will supply heating current tothe cathodes of each of the electric discharge devices of the radio transmitter and energizing current to the time limit relay 82, and generator GrB will supply space current through resistances 67 and 68 to each of those devices. After suflicient time has elapsed to permit the cathodes to become fully heated, time limit relay 82 operates to close contacts 83 preparatory to short-circuiting resistance 68, whenever contact 84 of antenna relay D is closed.

For reception the radio receiver 87 is used in well known manner.

For transmission the switch 91 is closed operating relay 92. In turn antenna relay D connects the antenna 57 to the radio transmitting apparatus through contacts 94 and 95 of the antenna switch and conductor 56. At the same time contact 84 is closed completing the short circuit about resistance 68. This decreases the normal negative polarizing potential on the grids or control elements of the amplifier L and discharge devices 50 and 62 and permits full magnitude space current to flow through each of these devices. The oscillator thereupon produces radio frequency oscillations in the antenna 57. The radio lamp 100 automatically lights to indicate to the studio attendant that the apparatus in the radio room is ready to function.

For transmission from the studio, transmitter switch 8 is thrown to its lower closed position. The studio attendant now has complete control of the broadcasting equipment, and, when it is desired to transmit, switch 103 is closed. Thereupon studio broadcast lamp 101 in the radio room lights up to indicate to the radio attendant that the studio is broadcasting and broadcast ace. HMUIMNE QNERQY.

lamp 106 in the studio lights up to warn persons in the studio that sounds originating therein will be broadcasted.

Sound waves originating in the studio A are impressed upon the transmitter 4 and the audio-frequency power delivered by the transmitter is in turn impressed upon the amplifier B through the transmitter switch 8, conductors 21, 22 and 23 and the input transformer 24. This power is amplified by means of the electron discharge devices 10, 11 and 12 and the amplified power is then impressed upon the input transformer 73 of the radio transmitter at C by means of the closed front contacts of relay 44 and conductors 40 and 41.

If it is desired to broadcast by means of the radio room transmitter 9 instead of the studio transmitter 4, the transmitter switch 8 is thrown to its upper position, in which case, the broadcasting equipment is under the control of the radio attendant at switch 105 instead of under the control of the studio attendant at switch 103.

The modified arrangement of control cir cuits of Fig. 3 will now be described. These circuits are to be considered in conjunction with amplifier B of Fig. 1 and radio transmitter C, and antenna switch D of Fig. 2 to form a complete system. The same reference characters are used throughout the drawing to designate the same elements.

The triple-pole double-throw transmitter switch 8 of Fig. 2 is replaced by the two position key 153 at Fig. 3. When the transmitter key 153 is thrown to its lower position the transmitter 4 in the studio is connected to the input of the amplifier B by means of conductors 21, 22 and 23. When the transmitter key 153 is thrown to its upper position the radio room transmitter 9 is connected to the input of the amplifier B over conductors 21, 22 and 23. Radio lamp 100 in studio A is lighted by the closure of switch 91 only during such time as transmitter key 153 is thrown to its lower position. Thus, the radio lamp 100 can only be lighted when the circuit is completed for broadcasting from the studio. A radio broadcast lamp 154 is lighted when the transmitter key 153 is thrown to its upper position and the circuit is in condition for broadcasting from the radio room by means of transmitter 9. The lighting of radio broadcast lamp 154 gives warning to any one in the radio room that sound waves originating therein will be broadcasted.

A loud speaking receiver 98, provided for monitoring purposes, may be connected by means of two position key 155 either to the audio frequency input circuit of the radio transmitter by way of conductors 151 when the key 155 is thrown to its upper position or to a monitoring radio receiver 156 when the key 155 is thrown to its lower position. The monitoring receiver 98 is automatically disconnected from conductors 40 and 41, when the key 153 is thrown to its upper position for transmitting from the radio room. The loud speaker is so disconnected in order to prevent singing by retransmission of received sound. For monitoring on the audio frequency input circuit of the radio transmitter, when the key 153 is thrown to its lower position for broadcasting from the studio, the key 155 is thrown to its upper position. The circuit for the monitorin loud speaking receiver 98 may be traced from conductors 40 and 41 extending between the amplifier B and the radio transmitter C, conductors 151, closed upper contacts of key 155 (normally open), conductors 160, the two left-hand closed upper contacts of key 153 to monitoring loud speaking receiver 98. For listening on the monitoring radio receiver 156, key 155 is thrown to its lower position and the circuit may be traced from monitoring radio receiver 156, closed lower contacts of key 155 (normallyv open), conductors 160, the two left-hand closed upper contacts of key 153 to the loud speaking receiver 98. The resistance 161 replaces the radio frequency receiver 98 across the conductors 151 when the key 155 is either in the neutral position or thrown to its lower position for connecting the loud speaking receiver 98 to the monitoring radio receiver 156.

Double contact relay 162 replaces the single contact relay 102 of Fig. 2. When the key 153 is thrown to its lower position for broadcasting from the studio, relay 162 is energized over the same kind of a circuit as previously described for relay 102 and which may be traced from the negative terminal of battery 13, switch 91, winding of relay 44 by way of conductors 150, right-hand lower closed contact of key 153, winding of relay 162, switch 103, conductor 163, to the positive terminal of battery 13. The opera tion of relay 162 causes studio broadcast lamp 101 in the radio room and broadcast lamp 106 in the studio to light. The resist ance 164 is employed to compensate for unequal voltage requirements of lamp 101 and 106.

For intercommunication between the studie and the radio room, hand telephone sets 170 and 171 are provided. Current for each of these sets is supplied from battery 13 over a circuit which may be traced from the negative terminal of battery 13, upper winding of retardation coil 172, hand sets 170 and 171 in parallel, provided the push button contacts are closed, lower winding of retardation coil 172, to the positive terminal of battery 13. Call lamps 173 and 174 are provided respectively in the studio and the radio room. Lamp 173 is lighted by means of push button 175 in the radio room and lamp 174 is lighted by push button 176 in the studio. In parallel with the lamp 173 is a buzzer 177, the circuit of which is controlled by switch 178. Likewise connected in parallel with the lamp 174 is a buzzer 179, the circuit of which may be closed by switch 180. Current for operating both the lamps 173 and 174 and the buzzers 177 and 179 is obtained from battery 13.

The method of operating the broadcasting system employing the control circuits of Fig. 3 is quite similar to the method followed when using the control circuits of Figs. 1 and 2. WVhen the switch 91 is closed, placing the radio apparatus in condition for transmitting and when the transmitting key 153 is thrown to its lower position for broadcasting from the studio, the radio lamp 100 is lighted, indicating to the studio attendant that all is in readiness for broadcasting from the studio. When the switch 103 is closed by the studio attendant the amplifier B is connected to the radio transmitter C by relay 4:4: and broadcast lamp 106 in the studio and studio broadcast lamp 101 in the radio room are each lighted respectively to warn persons in the studio that sounds originating therein Wlll be broadcasted and to indicate to the radio attendant that the apparatus is in condition for broadcasting from the studio. The radio attendant, by means of loud speaking receiver 98 can monitor the audio-frequency waves impressed upon the radio transmitter by throwing key 155 to the upper position or the radiated energy of the radio transmitter by means of the monitoring radio receiver by throwing key 155 to its lower position.

For broadcasting from the radio room the transmitter key 153 is thrown to its upper position in which case radio broadcast lamp 154 is lighted to warn persons in the radio room that sounds originating therein will be broadcasted. Simultaneously, monitoring loud speaking receiver 98 is disconnected to prevent singing.

From the foregoing description it is seen that a radio broadcasting system has been provided in which both the audio-frequency apparatus, radio frequency apparatus and supervisory signals are so interconnected that the apparatus will be operated in proper sequence and that the attendants in both the studio and radio rooms will be continuously advised of the circuit conditions of the apparatus. While the invention has been described in connection with two of its embodiments, it will be obvious to those skilled in the art that other modifications of by the accompanying claims.

What is claimed is:

1. The method of operatinga radio telephone broadcasting system which comprises producing audio frequency electric waves by means of sound waves, producing radio frequency waves, radiating said radio waves and automatically preventing an attempt to modulate said radio waves with said audio frequency waves except during such time as said radio waves are being radiated.

2. In a radio telephone broadcasting system, having a radio room and a studio, the method of operatin said system which comprises producing an i0 frequency waves by means of sound waves in said studio, producing radio frequency waves in said radio room, radiating said radio waves, automatically preventing an attempt to modulate said radio waves with said audio frequency waves except when said radio waves are being radiated and automatically indicating to the studio that radio waves are being radiated.

3. I11 a radio telephone broadcasting system, an antenna, a radio transmitter for modulating radio frequency power in accordance with audio frequency power, a source of audio frequency power, means to connect said radio transmitter to said antenna, and means effective only when said radio transmitter is connected to said antenna to connect said source of audio frequenqy power to said radio transmitter.

4. n a radio telephone broadcasting system, a radio room and a studio, a radiating system, a source of audio frequency waves located in said studio, a radio transmitter whereby radio waves are modulated in accordance with audio frequency waves, means for impressing said radio frequency waves upon said radiating system, a second means for impressing said audio frequency waves upon said radio transmitter, a third means in said studio effective upon the operation of'said second means to impress audio fre quency waves upon said radio transmitter providing said first mentioned means has been actuated to cause radio frequency waves to be impressed upon said radiating system.

5. In a radio telephone broadcasting system, a radio transmitter whereby radio waves may be modulated by audio frequency waves, a first source of audio frequency waves, a second source of audio frequency waves located at a distance from said first source and said radio transmitter, means to connect either said sources separately to said radio transmitter and an indicating device for said first source automatically operated by the connection of said second source to said radio transmitter.

6. In a radio broadcasting system, a radio transmitter for modulating radio frequency 25o, aao aar scissor,

waves in accordance with audio frequency waves, an antenna, an antenna switch for connecting said radio transmitter to said antenna, an audio frequency amplifier, a relay for connecting said amplifier to said radio transmitter, a source of audio frequency waves, a manually operated switch for connecting said audio frequency source to said audio frequency amplifier, a switch near said audio frequenc source for controlling the operation of said relay, an indicating device near said audio frequency source to automatically indicate both that the radio transmitter is connected to the antenna and that the audio frequency source is connected to said audio frequency amplifier and a second indicating device near said first device and a third indicating device near said audio frequency amplifier, said second and third devices being automatically actuated when said relay is actuated.

7. In a radio broadcasting system, a radio transmitter for modulating radio power in accordance with audio frequency power, a radio frequency power output circuit and an audio frequency power input circuit for said radio transmitter, an antenna, an electrically operated antenna switch for conmeeting said radio output circuit to said antenna, a source of audio frequency power, a relay for connecting said audio frequency source to said radio input circuit, a switch for controlling the operation of said relay, and a second switch controlling the operation of both said antenna switch and said relay.

8. In a radio telephone broadcasting system, a studio, a radio room, means in the radio room for radiating radio frequency power, means to indicate to the studio that radio frequency power is being radiated, means in the studio for furnishing audio frequency power for modulating said radio frequency power, and means in the radio room for indicating when said last mentioned means in the studio is ready to function.

9. In a broadcasting station, a studio, a radio room, means whereby a person in either room may broadcast, and means in each room to automatically indicate that the circuits are in operating condition for broadcasting from that particular room.

10. In a broadcasting station, a radio room, means therein for controlling the operation of a radio transmission system, a studio, means in said studio for automatically indicating if said radio system is in transmitting condition, and means in said radio room to indicate that someone in the studio is ready to broadcast.

11. In a broadcasting station, a radio room, means therein for controlling the operation of a radio transmission system, a studio, means in said studio for automatically indicating if said radio system is in transmitting condition, and means in said radio room for automatically indicating that someone in the studio is ready to broadcast.

12. In a broadcasting station, a radio room, radio transmitting apparatus located therein, a studio, and means for automatically indicating in said studio that said radio apparatus is in transmitting condition.

13. In a radio telephone broadcasting system having a radio room and a studio, a method of operating said system which comprises producing audio frequency waves in said radio room and automatically indicating to thev studio that radio waves are being produced.

14. In a broadcasting station, a radio room, a studio, means in both said rooms for jointly controlling the operation of a radio transmission system, and means for automatically indicating in either room the condition of the control apparatus in the other room. I

In witness whereof, I hereunto subscribe my name this 11th day of August A. D.,

FRANCIS M. RYAN.

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