Patent GB-242266-A (GB)
Title: Systems of radio broadcast distribution
IPC: H04H20/77
Filed: 1925-10-21
Abstract: 242,266. Colladay, E. F., (Assignee of Clement, E. E.). Oct. 28, 1924, [Convention date]. Transmitting and receiving systems; relaying or repeating systems; thermionic amplifiers, detectors, and modulating systems; wired wireless systems. - A broadcast service is maintained by radiation, or alternatively over an existing telephone system, throughout an organized network of centres A, B C, D, Fig. 1<a>, arranged in district, regional, and local groups each having a characteristic permanent operating frequency. The system is characterized by the use of fixed carrier waves for linking the master transmitting stations to selected relay centres, the receiving plant of each relay station being permanently tuned to its allotted frequency. The district stations B are linked to a master station A through the ether and also by trunk lines 58, 59, 60, the same alternative line connection existing between district stations and the regional centres C and wave subscribers D. The allotted carrier-wave frequencies are in a descending order throughout the groups B, C and D. Normally a doublymodulated carrier wave is utilized, and incoming signals received on one frequency at station B are retransmitted on another frequency appropriate for reception by stations C, from which they are again radiated at the carrier frequency allotted to station D reception. Although each subscribers outfit D is tuned to a definite carrier wave, he is able bv means of suitable filter circuits, to select different intermediate frequencies, and thereby ensure a variety in the broadcast items simultaneously available. National, district and local programmes are made up day by day from which the subscribers can make any desired selection. Provision is also made for ensuring that items of importance are distributed to distant centres at appropriate geographical times. If necessary permanent records can be made at the local receiving station for subsequent reproduction at a more convenient time. Supervision, metering, and testing are carried out at the local telephone exchange, or at an associated radio exchange. Where singly-modulated transmission is employed, interference is prevented by allotting different carrier-wave frequencies to adjacent B districts and to adjacent C sub-districts. Broadcast distribution. Broadcasting can originate at either stations A, B or C, Fig. 1<aa>, through microphones 64 and suitable amplifiers 65, 69 72 and intermediate frequency modulators 66, 70 and 71, or from station D over a line 18, 19. In each case it can be distributed either generally as from A, or in a certain district D, or in selected trial areas C only. When radio neception is difficult owing to atmospheric conditions, distribution is effected over the telephone network, so as to maintain a definite average of efficiency throughout the entire system. Wherever the broadcast originates, the initial audio frequencies are modulated at an intermediate frequency, as soon afterwards as possible, and are subsequently superposed either on a radiated carrier wave or are fed to a line circuit. Inter-station connections. For example, speech from station A<1> (D type), Fig. 1<aa>, passes from the jack J<1> to J<13>, through an amplifier 65 to an intermediate-frequency modulator 66 and thence through jacks J<14> and J<4> to the local radiating antenna 53. Alternatively the modulated energy from 66 may pass from jack J<14> to jack J<5> to the line 50 for radiation (at station C reception frequency) from the antenna 55 of station B. Alternatively it may be re-transmitted over the trunk line 51 to station A for universal distribution from the master antenna 57. The second or carrier-wave modulation is in each case effected on the modulators T, T<1> or T<2>. In order to allow reception and supervision of the audio-frequencies at each station the operators circuits are provided with demodulators 72, 74, 76 and receiving phones 73, 75, 76 in addition to the ordinary telephone head gear 81, 82, 83. Subscriber and local exchange. Fig. 3a shows a typical subscriber's superheterodyne radio receiving installation A<1> connected through the ordinary telephone outfit, and the local exchange (not shown) to a type C station and its associated radio switchboard R. The top wires 18<c>, 19<c>, 19<d> from the telephone outfit are connected to the radio receiver through a cut-off relay L<4> which is bridged by a voice by-pass condenser q<2>. The filament and plate battery circuits of the radio receiver are closed either through the relay L<5> controlled from the central radio switchboard or from the hand switch hook H<1>. By pressing a button switch h, the subscriber can also take ordinary calls through the transmitter T<1> and receiver t<1> from the telephone line, though he cannot normally originate telephone calls from this point. He can also broadcast through the central-station plug J<2> via the amplifier t<2> and modulating and radiating equipment T. A supervisory lamp s<2> and a tone test commutator P<5> are inserted in the operator's circuit through a plug P<4>, which also maintains the battery B<1> in series with the. filament battery A<1> at the subscriber's station and serves to keep the latter battery under constant charge. Reception divided between subscriber and exchange. Fig. 3<b> shows a modified system in which part of the demodulating process is relegated to the central exchange equipment. The subscriber at A<1> calls for radio service by moving his receiver a rapidly up and down. The telephone operator at C thereupon transfers the call to the radio operator at R, who inserts plugs P<12>, P<13> into jacks J<17>, J<18>. Incoming waves received on the subscriber's antenna 28 pass first through the local demodulator 85 which detects the intermediate signal frequency. This is then transferred through tuned couplings 121, 123 and 115, 117 to the second demodulator 86 located at the central station. The resulting audio-frequencies are returned through plug P<12> to the line wires 18, 19 and thence to the subscriber's telephone or loud-speaker a. Exchange control of amplification. The centralstation amplification service may be divided into classes suitable for headphone, table speaker, or loud-speaker reproduction, and charged for accordingly. The usual line-meter LM is utilized for registering the costs through a push-button g which periodically connects the generator G through a commutator g<1> to actuate the recorder 301 via the relay L<3> and meter LM. Subscriber connected by wire only to exchange. Alternatively, as shown in Fig. 3g, incoming signals are first detected and amplified in the tube circuits 400, and the intermediate frequency is transmitted over the subscriber's line 406 to the final detector 408, which has no receiving antenna, a double-pole switch 410 allowing the central station to supervise the quality of the reception. Or the whole of the demodulation equipment may be located at the central station, and audio-frequency currents alone supplied to the subscriber's outfit, with or without the interposition of amplifiers. Automatic switching-means of known type may be provided to allow such a subscriber to select any given item from the variety available. Station relaying equipment. Fig. 5<bb> shows a typical station B or C relaying equipment by means of which incoming doubly-modulated energy from the antenna 54 is demodulated, and the intermediate-frequency currents superposed upon the new carrier-frequency allotted for reception by the next lower group of stations. Normally the received radio energy undergoes first detection in the tube 170, amplification of the in. termediate frequency in the tube 171 and remodulation at the new carrier frequency in the tubes 172, 173 feeding the transmitting aerial 55. By suitably plugging in the trunk lines 50, 51, modulated carrier waves from the line 50 or 51 can be radiated from the antenna 55, or these currents can be relayed from one trunk to another. Or received radio energy from the antenna 54 can be relayed to trunks 50 or 57. A suitable recorder 321, intermediate frequency oscillator 322, and modulator 323 and reproducer 324 enables incoming signals to be stored up in permanent form for subsequent re-transmission at any suitable time. Traffic and programme administration. Charts are given in the Specification showing a desirable allocation of the broadcast service relatively to the normal telephone traffic for city and rural areas. Daily programme or dispatch sheets are made up by each station for administrative purposes and for the information of subscribers to the broadcast service. According to the Specification as open to inspection under Sect. 91 (3) (a), in order to ensure synchronism throughout the system a master frequency may be transmitted from station A, from which harmonics are built up at the intermediate stations to serve as the local re-transmission carrier frequency. This subject-matter does not appear in the Specification as accepted.