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US2028212.Pdf \J-mfzl, 193s.‘ } ' ' 'R. A. HEISING 2,028,212 RADIO TRANSMITTING SYSTEM ' ‘ ; , ‘ ' lFileq’vec. 22, 1935 .5 Sheets-Sheet 2 BASE 7 FIG. 3 ' . 1 2’ v ‘ racaueucv ,9‘ 1 > 20 ' HARMONIC :3 GENERATOR _ I8 , " ‘ > ‘ || ' ' _ ' 30 | l 22 25 26 27 29 l 1 J ) I) |--- HARMONIC — SELECTOR — PHASE - ' :‘GENERA'WR ._ CIRCUITS __ SHll-‘TER M°°ULAT°R ll 28 B’ um, ATTORNEY ‘ Patented Jan. 21, 1936 2,028,212 UNITED ‘ STATES PATENT OFFICE ‘ 2,028,212 ‘ RADIO TRANSMITTING SYSTEM Raymond A. Heising, Summit, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York ‘ ‘ Application December 22, 1933, Serial No. 703,514 9 Claims. (Cl. 250-9) This invention relates to radio broadcasting sions from the transmitting circuits of Figs. 1 system employing very short waves and, in par and 3. , ticular, to e?icient transmitting and receiving Referringto Fig. 1 a base frequency source I ‘ circuits for such systems. a , produces oscillations of, for example, 10,000 cycles A feature of the invention is a system in which and supplies them to a harmonic generator 2 5 a plurality of related frequency carrier waves are associated with which are a plurality of harmonic relatively so phased as to permit the use of a selector circuits 3, 4, etc. each designed toselect common ?nal ampli?er of much lower e?‘ective an individual harmonic of the base frequency output than the aggregate of the peak outputs wave falling within the ordinary broadcast range. The harmonic generator 2 ‘and the selector cir-I 10 H) of the individual carrier waves. _ Another feature of the invention is areceiving cuits 3, 4, etc. maybe of well-known types. The system for distributing multiplex short wave base frequency source, although not necessarily broadcast transmitters to broadcast receivers at so limited, is illustrated as connected to a prime apartment houses by the use of unmodulated lo source of ultrahigh frequency waves 5 through cally‘generatedshort wave oscillations which are a frequency divider or sub-harmonic generator 15 caused to interact with the received short waves 6 of the multi-vibrator type.‘ Such ultrahigh fre to produce modulated beat frequency waves with quency sources and frequency dividers are well in the usual broadcast range thus enabling very known in the art. The high frequency source 5 short wave broadcast programs to be effectively which is preferably a vacuum tube oscillator con handled by the local broadcast frequency dis trolled by a piezo electric crystal has an output 20 tributing network of the apartment house. circuit connected, to a harmonic generator and In accordance with the invention, a plurality selector 1 which serves to, derive and impress of carrier waves lying within the present-day ultrahigh frequency waves upon the input cir broadcasting frequency range are each modulated cuit of a power ampli?er 8. These ultrahigh fre by a broadcast program or transmission individual quency waves may, for example, be of the order 25 thereto. These carrier waves which are prefer of 30 megacycles or higher. ably produced as harmonics of the same base fre Each harmonic selector circuit 3, 4 is associated quency oscillations so as to control their frequency with an individual broadcast channel and since. I spacing are given suitable relative phase dis these channels are alike except for the carrier placements before being modulated. After modu frequencies and the fact that they do not trans- 30 lation they are caused to modulate a common mit the same program a description of one will ultrahigh frequency carrier wave, their phase dis suffice for each. Selector circuit 3 selects an ap placements serving to prevent coincidence of their propriate wave withinthe ordinary broadcast band ‘ peak outputs whereby the ?nal ampli?er may as, for example, one‘megacycle and impresses it have a much lower power rating than, would upon a phase shifting network 9 of well-known 85 otherwise be possible. ‘ type which is variable to permit adjusting the a. The invention may be readily understood from amount of phase shift as may be desired. After ' the following description taken in connection with undergoing phase shift the oscillations are im the appended drawings in which pressedupon an ampli?er l0 and the ampli?ed ,Fig. 1 illustrates schematically the circuit of a oscillations are supplied to an intermediate, fre- 40 multiplex radio broadcast transmitter; quency ampli?er‘ l I. A program orspeech input Fig. 2 indicates'the initial phase relationships ‘ circuit I2 is associated with ampli?ers l3 and H, of the intermediate frequency carrier waves; the output circuit ‘of the latter of which is induc Fig. 3 illustrates schematicallyra modi?cation tively. connected to the platecircuit of ampli?er 45 of the circuit of ‘Fig. 1 in which in lieu of succes I l in accordance with the well-known plate mod- 45 sive modulation, a separate unmodulated carrier ulator ampli?er circuit of U. S. Patent to Helsing, wave is transmitted; . i No. 1,823,322 issued September 15, 1931, whereby Fig. 4 is a diagram indicating two different ar the one megacycle oscillations are modulated by rangements of the modulating frequencies of the the ampli?ed program currents from circuit II. unmodulated and modulated carrier waves of Fig. In similar fashion the intermediate frequency 50 .50 carrier wave supplied to intermediate ampli?er 3, and V y - _ a, Figs. 5 and 6illustrate apartment; house receiv I5 is modulated by the program‘ or other currents ing and distribution systems adapted to receive of its respectively associated speech or program at‘ will either ordinary broadcast transmissions input circuit. ' 55 or the ultrahigh frequency broadcast transmis The modulated intermediate frequency waves 55 2 2,028,212 produced in the output circuit of ampli?er ii waves these two conditions of periodic phase co are transmitted through a band pass ?lter l6 incidence and proportionality of phase to fre and impressed, in series with the plate supply quency are inseparable it follows that periodic emf. derived from source H, on the plate circuit phase coincidence may be avoided by ‘imparting of power ampli?er 8. In like manner each of the to the harmonically related waves arbitrary ini other modulated intermediate frequency waves is tial phases related in some random manner de impressed through its respective band pass ?lter parting widely from that of proportionality to It on the series plate circuit of power ampli?er frequency. - 8. The band pass ?lters l6 serve to con?ne the Stated somewhat differently the relationship modulated wave bands .which they respectively 10 between phasev of vectors and their frequencies 10 transmit to their appropriate ranges eliminating is such that if this left-hand diagram represents any harmonics or other components which might vwhat occurs at one instant, the middle diagram fall in the range of and interfere with any of the representswhat will occur at some later instant other intermediate frequency bands. They also and there will be found at all times an orderly exclude bands from other channels from the arrangement of phase of vectors with respect to plate circuits of their respective intermediate their frequency. To prevent the situation por frequency power ampli?ers, thus preventing un trayed by the left-hand diagram from ever occur desired intermodulation which might result in ring, we must set up. as an initial condition a cross-talk or interference between two different disorderly relation of phase angle with respect program channels. Accordingly, oscillations of to frequency which is what is shown in the third 20 the extremely high frequency produced by the diagram of Fig. 2. Once a disorderly arrange harmonic generator ‘I are simultaneously modu ment ‘is set up, the phase agreement of all the lated in the modulating ampli?er 8 by all of the vectors as illustrated in the left-hand diagram modulated intermediate frequency carrier waves. will never occur. From another viewpoint, a 25 These modulated high frequency oscillations are random phase arrangement of the various vectors transmitted in the usual manner to an antenna is what is desired. or a transmission line. ' ' Referring again to Fig. 2, the third diagram In Fig. 2, certain phase relationshipsof the un shows one arbitrary phasing of the components modulated carrier waves are illustrated. Assum in accordance with the present invention. As 30 ing that the various intermediate carrier fre-v sume that the-vectors a, b, c, d, and e as gener quency waves originated as harmonics of the ated were in phase coincidence at their maxima same fundamental frequency wave, it will be ap as indicated in the ?rst diagram. Suppose that parent that at a particular instant the maximum the 10th harmonic vector a be utilized in its po of the fundamental wave will coincide with the sition of a" as generated. The 11th harmonic 35 maxima of each of the harmonics. At that in b may be advanced 135° to b". The ‘12th har 35 stant, therefore, the phase relations of the vari- monic 0 may be-advanced45“ to c". The 13th ous harmonics selected as intermediate fre and 14th harmonics may both be advanced 270° quency carrier waves may be represented by the or what is the same thing retarded 90°. It will , vectors of the diagram at the left of Fig. 2. The be apparent that this arbitrary phasing so de 40 power which the aligned vectors represent at that parts from frequency proportionality that the instant is proportional to‘ the square of their condition essential to maximum amplitude coin- ' vector sum or twenty-?ve times the power which cidence is avoided.
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