US1721627A - Radio transmission system - Google Patents

Description

July 23, 1929.

IIII

Patented `luly 23, 1929.

UNITED STATES PATENT OFFICE.

LAWRENCE C. F. HORLE, OF NEWARK, NEW JERSEY, ASSIGNOR T0 FEDERAL TELE- PHONE MANUFACTURING CORPORATION, OF BUFFALO, NEW YORK, A CORPORA- TION OF NEW YORK.

RADIO TRANSMISSION SYSTEM.

Application filed August 6, 1924. Serial No. 730,485.

This invention relates to radio transmission systems and more particularly to a transmission system in which a number of radio broadcasting stations are arranged for simultaneously radiating speech signals or other signals originating in a single master control station connected by line wires to the broadcasting stations.

It has been proposed heretofore to broadcast speech or other radio'signals, originating at a central master station, simultaneously from widely separated stations by transmitting to all of the broadcasting stations the speech or other signal wave over line wires from the master station, each station of the group of broadcasting stations generating its own individual carrier wave, independently of the master station, and the carrier wave of any given station having a wave length different from that of others of the group. In such systems the energy received over the line wires from the master station has carried only the audio* frequency speech or signal wave which has then been impressed upon the various carrier waves of the broadcasting stations as a modulating component of these carrier waves.

It is frequently desirable, however, that the speech or other signals thus originating in a master station and transmitted over line wires to a group of radio broadcasting stations be radiated from all the members of the group of broadcasting stations on carriers of the same, instead of different, wave length for the individual stations of the group. But in order that such broadcasting of the same speech or other signal on the same carrier wave length from a number of stations simultaneously may be accomplished satisfactorily, it is imperative that the wave lengths of the carriers radiated from the individual members of the broadcasting group be maintained indentically the same. If these carrier wave lengths' from the respective stations are permitted to differ, reception of the broadcast radio signals by a receiver so situated as .to be within the broadcasting range of more than one of the group of stat-ions becomes ditlicult or impossible, because of bea-ts due to the difference in wave length of the carriers radiated from the various stations.

To obviate this dihculty in reception of the broadcast modulated signal Waves from the group of stations, it is proposed to provlde an arrangement such that the energy transmitted over line wires from the master station may not only act to modulate the carrier waves of the several broadcasting stations with a speech or other audible component but may also act as a control means so related to the transmitting means at the several stations of the broadcasting group that the carrier waves radiated from the said several stations are maintained at the same frequency each to each. This control of broadcasting frequency of the `carrier waves radiated from a number of interconnected stations by means of energy transmitted over line wires from a distant master control station cannot, however, be attained by the direct transmission, over the wires, of a carrier wave having a frequency equal to that of the radio waves which are to be radiated as carriers from the broadcasting stations. As is well known, the transmission over line wires of waves of the order of radio frequency, that is, of the enormously high frequency usual in radio tele-l phony broadcasting. and from a control station to a distant broadcasting station, is impracticable, due to causes well recognized in the art, such as attenuation and distortion which increase with the frequency. Further. it is obvious that the problem of main taining the frequency of the carrier waves radiated from the several stations equal to each is also notto be solved by attempting to change the frequency of these broadcasting carrier waves to meet the conditions imposed by transmission over long line wires, since this procedure means a reduction of the broadcasting frequency to the frequency suitable to line wire transmission, and consequently to a point far below that required in practice for radio telephony. The solution of the problem, therefore, of so controlling, over line wires, the carrier waves of a group of broadcasting stations from a distant master control station as to hold the frequencies of these broadcasting carrier waves identically the same, calls for means and methods which permit the full use of such line wire carrier wave frequencies, say 10000 to 20000 cycles, as have been found efficient in line wire transmission, and at the same time it calls for means and CIK M retained all the advantages inherent in the usual method of simultaneous broadcasting on different wave lengths from several stations of the speech or other signals transmitted overline wires from a master station, and in which, further, may be fully Vrealized the advantages inherent in the method of broadcasting, simultaneously from'such groups of stations, on the same wave length.

`Inaceordance with the invention, energy in the form of a line wire carrier wave, of a frequency best suited to line wire transmission, is sent over line wiresto the several stations of the broadcasting group. This line wire carrier wave is impressed upon suitable means at each of the stations, by which the wave is amplified, and changed in frequency to the high value required for broadcasting, the frequency of the broadcasting wave being, however, maintained the same for all members of the group of broadcasting stations. At some point in the carrier wave path through the complete system of master control station and broadcasting station, the carrier wave is modulated by a speech or other audio frequency signal wave provided through the action. of suitable mea-ns in the master control station. The amplified and modulated high frequency waves are finally rediated in the usual manner simultaneously from the several stations of the broadcasting group.

The invention will be best understood as to organization and method of operation and as to its other objects and advantages by reference to the following detailed description 'and to the drawings, which illustrate two embodiments of the invention.

Figure 1 represents schematically an embodiment of the invention in which a speech or other audio frequencysignal Wave and a line wire unmodulated carrier wave. are separately transmit-ted from control station to broadcasting station.

Figure 2 represents schematically an embodiment in which a modulated line wire carrier wave is transmitted from control station to broadcasting station.

Figure 3 is a diagrammatic illustration more in detail of certain apparatus utilized in lthe Vembodiment shown in Fig. 2.

The saine part wherever it appears in the various figures will be lrepresented by the same reference character.

Referring to Fig. 1, a master control station 1 comprises apparatus represented schematically by 2 for generating speech or other signal waves and also comprises apparatus represented by 3 for generating a line wire carrier wave. Broadcasting stations as 4 and 5 are-located at a distance from control station 1. Each of the broadcasting stations comprises the following apparatus represented schematically in the figure: Speech or other signal supply waveamplifier 0; line arrier wave distortion amplifier 7; wave filter 8; radio frequency amplifier 9; modulator and radio frequency power amplifier l0; transmitting antenna 11. Line wires 12 connect the line carrier wave generating apparatus 3 of the master control station 1 to the line carrier wave distortion amplifier 7 of a broadcasting station, as station 4. Line 'wires 13 connect the speech or other signal wave generating apparatus 2, of the master control station 1, to the signal wave amplifier 6 of a broadcasting station. In operation, a carrier wave of a frequency above andibility but of the low value required in efficient line wire transmission, and of the order, for example of 10000 to 20000 cycles, is generated by any suitable means in wave generating apparatus 3 of the master control station. The carrier wave is transmitted in a usual manner over line wires 12 to distant broadcasting stations Lich as 4L and 5. At a given broadcasting station the wave, of line wire carrier frequency, is distorted by any well known and suitable means as by a distortion amplifier 7 to produce a desired harmonic frequency of the said incoming line wire carrier wave. This desired harmonic is selected by wave filter 8 through which the wave from the distortion amplifier is passed. rfhe frequency of the line carrier wave transmitted over the line wires 12 and used as a basis for the harmonic is so chosen that the said harmonic is of the frequency desired for the radio frequency wave which is to be broadcasted from the stat-ion. The radio frequency carrier wave resulting from the selective action of wave filter 8 is suitably amplified as by R. F. amplifier 9. The mochilation of this radio frequency carrier wave from amplifier 9 is effected by means of a speech or other audible signal wave transmitted from audible signal wave generator 2, over line wires 13, through audible signal amplifier 6 to the modulator and R. F. power amplifier 10. In this modulating and amplifying apparatus 10 the amplified audible signal wave is impressed upon theamplified R. F. carrier wave, and the resulting modulated R. F. wave'is then broadcasted in the usual manner from antenna 11.

Referring to Fig. 2, a master control station 14 comprises apparatus represented by 15 for generating speech or other signal waves in any suitable manner as by the same means as employed in the apparatus 2 of Fig. 1. The control station 14 also comprises speech or ot-her audible signal amplifier 16, and line carrier wave generator and modulator 17. Broadcasting stations, as 18 and 19, are located at a distance from control station 14. Each of these broadcasting stations comprises the following apparatus: modulated line carrier wave distortion amplifier 20; wave filter 21, radio frequency power amplifier 22; transmitting antenna 23. Line wires 24 connect the line carrier wave generator and modulator 17, of the master control station 14, to the distortion amplifier 2O of the broadcasting station. In the operation of the system as arranged in Fig. 2, a carrier wave of a frequency above audibility but of the comparatively low frequency required for eflicient` line wire transmission is generated at the master control station by any suitable means such as by apparatus represented at 17 A speech or other audible signal wave generated by any usual or known means as -by audible signal Wave generator 15, and suitably amplified as by signal wave amplifier 1G, is impressed at the master control station upon the'line wire carrier wave, as by means of the apparatus represented by the line carrier wave generator and modulator 17. The modulated line carrier wave is then transmitted, essentially as in the case of the line carrier wave of Fig. 1, over line Wires 24 to distant broadcasting stations such as 18 and 19. At each of the broadcasting stations the modulated line carrier wave is distorted, as by distortion amplifier 20, to produce a harmonic of the incoming Wave, and the desired harmonic is selected as by wave filter 21. As in the case of the line carrier wave of Fig. 1, the frequency of the line vcarrier Wave used as a basis for the harmonic is such that the said harmonic is of the frequency desired for broadcasting. The modulated radio frequency wave from filter 21 is suitably amplified as by R. F. amplifier 22 and is then broadcasted from antenna 23.

The preferred embodiment of the invention which is outlined schematically in Fig. 2 is illustrated more in detail in the diagrammatic representation of Fig. 3, which shows apparatus which may be used in a master control station and in a member of a group of broadcasting stations, as arranged in accordance with the invention. Referring to Fig. 3, a master control station 25 is shown, corresponding to master control station 14 of Fig. 2. A source of speech or other audio frequency modulating current supply 26, comprising microphone 27 and a current source 28 is coupled to amplifying means such as vacuum tube amplifier 29. The output of the amplifier 29 is passed through suitable transformer coupling means to a carrier wave generating and modulating means, as tube 30. The circuits of this tube are arranged in a usual manner for use of the tube as an oscillator for the generation of the carrier wave required for transmission over the line wires and also as a modulator of the carrier wave by the modulating speech or other audio frequency current impressed on the input circuit of the tube. The modulated linel carrier wave produced in tube 30 is transmitted over line wires, as 31 and 32, to the members of a group of broadcast-ing stations, one of which, 33, is represented in the figure. The carrier wave over line 31 is impressed upon the input circuit of a tube 34, the circuits of which are so arranged in a usual manner as by overloading the tube that the tube acts as a distortion amplifier of the line wire wave. The output circuit of tubev 34 is impressed upon any usual filter means represented by 35, by which a harmonic of proper frequency is selected. As explained in connection with Fig. 2, the harmonic selected is of the frequency required for broadcasting. The radio frequency modulated wave from the filter means 35 is'amplified as by power amplifier tube 36 and finally radiated from antenna 37.

The schematic Figures 1 and 2 and the more detailed diagrammatic Fig. 3 arel representative of embodiments of the invention in that they show the several conversions that. go on in the systems. It is to be understood, however, that in practice various additions to the apparatus illust-rated may be made, such for example as many stages of amplification where necessary. It is to be further understood that such additions, and

likewise many changes in the apparatus described and illustrated may be made without departing from the scope of the invention as defined in the claims.

What is claimed is:

1. A radio transmission system adapted to supply broadcast programs to a plurality of radio receivers and comprising a master control station and a group of radio transmitt-ing stations, a control frequency channel comprising line wires linking the control station and the transmitting stations, said transmitting stations beng spaced from each other by such distances that each individual member of the group may constitute a separate distributingcenter for radio broadcasting, whereby a given receiver may be Within the signal audibility range of one only or of a plurality of said group, means at the cont-rol station for generating a carrier wave for transmission over the control channel and having the comparatively low frequency of line wire carrier waves, means at the control station for generating a signal wave and means for modulating at the control station said carrier wave by the signal wave, means at each of the transmitting stations for increasing by the same amount the frequency of the modulated carrier Wave to a comparatively high radio carrier frequency, and means at each transmitting station for radiating the modulated carrier Wave of increased frequency.

2. A radio transmission system adapted to supply broadcast programs to a plurality of radio receivers and comprising a master control station and a group of radio transmitting stations, a control frequency channel comprising line wires linking the control station and the transmitting stations, said transmitting stations being spaced from each other by such distances that each individual member of the group may constitute a separate distributing center for radio broadcasting whereby a given receiver may be Within the signal audibility range of one only or a plurality of said group, means at the Control station for generating a carrier vvave for transmission over the control channel and having the comparatively low frequency of line Wire carrier Waves, means at the control station for generating a signal Wave and means for modulating at the control station said carrier Wave by said signal Wave,

distortion means at each of the transmitting stations for producing a harmonic of the modulated carrier Wave generated at the control station, means at each of the transmitting stations for increasing the frequency of said Wave by the same amount by filtering out adesired harmonic of the Wave, and means at each transmitting station for radiating the modulated carrier Wave of increased frequency. Y

3. In combination, a plurality of radio transmitting stations, a control station, a control frequency channel linking said control station and said radio transmit-ting stations, means for generating a control frequency associated with. said control frequency channel, means at the control station for modulating the control frequency by potentials varying at audio frequency, and means at each transmitting station for deriving a band of modulated radiation frequencies from said modulated control frequency.

In Witness whereof, I hereunto subscribe my name.

LAWRENCE o. F. HoRLE.

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