US1931631A - Transmitting - Google Patents

Description

TRANSMITTING Filed Feb. 25, 1932 INVENTOR WILHELM RUNGE ATTORNEY Patented Oct. 24, 1933 1,931,631 TRANSMITTING Wilhelm Runge, Berlin, Germany, assignor to Telefunken Gesellschaft fur Drahtlose Telegraphic in. b. 11., Berlin, Germany, a corporation of Germany Application February 25, 1932., Serial No. 595,000,

.andin Germany January 27, 1931 7 Claims.

This invention relates to a method of and means for transmitting modulated oscillations.

When modulating'the radio frequency oscillation or carrier wave produced by a transmitter,

j the waves amplitude grows transiently to nearly twice the :mean value. If a transmitter is to ad- ;mit of high degrees of modulation then the maximum power deliverable, as will be seen, must be practically four times as large as that of the mean value. Particularly where large powers are dealt with, this involves a large outfit of tubes, and these are mostly poorly utilized in the presence of mean values and low degrees of modulation. In what .follows an arrangement is going to be disclosed in which the tube. power required for a given carrier power is but half of what it has been heretofore.

According to the invention the arrangement re 'ferred to comprises two transmitters one of which is :not modulated and furnishes only the carrier wave, while the second one is modulated though separating by well-known means and ways the carrier wave and one side-band so that it furnishes only one side-band. In what follows a comparison shall be made as regards the power conditions of arrangements known in the earlier art and those here disclosed.

The carrier-wave amplitude shall be designated 'by i and the amount :or degree of modulation by m; the maximum or crest value of the current will than be l-i-m, and the minimum tube power heretofore required for the transmitter consequently will :be (1+m) .=1-j|-2m+-1n What is required according to the present novel method is a carrier amounting to l and a side-band oscillation amounting to m. The power incidentally needed is l+m It will be seenthat in the second case the portion of the power denoted by 2112 needed in the .former instance is saved. If .m: 1100 o/o, then :the power in the first case will be 4, in the second the power 2 will be consumed. In other words, one-half of the power is saved. 'Ihi-s situation holds good approximately down to 0/0,, while for lower modulations the saving 45 is smaller a In carrying the above method into practice difficulties would arise the attempt of cansing both transmitters to operate upon a common or joint useful circuit .or load (aerial). The high alternating current potential originatingxfrom the carrier transmitter would then be active also at the end or -power. tubes of the side-band transmitter and vice versa, and the result would be overmodulation in both power 5.5 tube sets. If the tubeswere to be dimensioned so amply that such overmodulation does not occur, one gets back again to exactly the same tube power of the modulated transmitter known in the art. In order to preclude mutual influence both outputs of the transmitters would have to be balanced out completely. But an attempt to insure such neutralization by connecting both transmitters in the diagonal of a bridge arrangement one arm of which consists of the useful circuit (antenna), while another arm thereof contains a simulation of the useful circuit, again is of no avail inasmuch as in that case one-half of the power would be dissipated in the said simulation, while substitution of this power by choosing over ample divmensions of the transmitters would mean again a double increase, i. e., increaseto the tube power heretofore usually required. However, this difficulty may be obviated according to the present invention by'causing both transmitters to work upon different aerials which are balanced out in reference to each other.

'Now, such neutralization of the two aerials may be accomplished most simply by mounting them a great distance apart and by feeding both antennae from the joint transmitter plant by way of long feed lines. But since two antennae located ,a great distance apart need two mast installations, the saving of one-half of tube equipment would be purchased at the cost of double mast installation. However, the distance between the aerials may be reduced considerablylby that both antenna by supplemental coupling means are so inter-coupled that the current induced by one of the aerials, in the other will be zero at the point where the transmitter is united. .Such balancing-out action is insurable in difierent ways and means. A number of embodiments shall be cited by way of example in what follows.

When mounting separately the antennae for radiating off the carrier wave and the radiation' of the side-band different receiving points will be reached by the carrier wave and the side-band in different phases,,according'-to the 5 location thereof. While in the transmission of two side-bands for the carrier a definite phase position is necessary (by shifting the carrier phase an angle of degrees in reference to the correct position reception is extinguished entirely), the, phase of the carrier wave will be immaterial when transmitting only one sideband. While in the mounting of antennae separection of the receiving station, to be sure, the incoming phase between carrier and side-band is different, the incoming volume will be the same in all directions inasmuch as it is independent of the phase.

To receive such a transmitter any standard type of broadcast receiver may be used. It will be advantageous, however, not to tune it exactly to the carrier of the transmitter, but rather detune it slightly toward the side-band that has been transmitted. If a plurality of neighboring transmitters send out only one side-band spaced up to 9 kilocycles, and if the distance of the carrier waves apart is each 9 kilocycles, it then becomes feasible to preferentially receive only one program, whereas in the earlier arrangement of senders with both side-bands it was invariably found that the undesired side bands of two neighbors were also included.

In what follows a diagrammatic circuit scheme is suggested:

Referring to the drawing, there is shown in Fig. l a known method for sending out but one side-hand without carrier and the other side band is used also. By way of terminals 1 a modu" lating current consisting of the voice or music is supplied. 2 is a modulator of known construction in which the radio frequency generator 3 is modulated by means of the tonal currents supplied at 1. If the generator 3 has a frequency hl and if the voice current comprises the frequency band between c and f, what then leaves the modulator is a frequency mixture which fills the band hl-l-f. This frequency mixture is fed to a band filter 4' one fundamental wave of which liesat hl-l-c, whereas theother one lies above hl-l-f. Of the frequency rnixture containing the carrier wave and two side-bands and which is fed to the band filter 4, as will thus be seen, there is passed only one side-band extending from hl-l-e to h-l-f. A band filter-of this kind can be constructed only when H1 is not unduly high since the carrier frequency hl is to be out oil? by the filter, while frequencies rather closely above the carrier are still to be passed. Hence, the band filter ies a general rule can not be built in a way so that 7L1 would constitute the desired carrier frequency to be sent out, in fact, hl must be considerably lower. In order that a higher carrier frequency may now be possible, the frequency band passed by the band filter 4 is fed to another modulator 5 wherein the frequency hZ fed to this modulator from the radio frequency generator 16 is modulated. At the output end or above the said modulator 5 there will then arise the following frequencies or frequency bands, to wit:

The upper side-band of the carriers and the lower side-band are so far removed from each other that it is readily feasible with one bandfilter 6 to filter out one of these side-bands, say, the upper one, while the carrier and the other side-band are suppressed. The passed sideband, optionally after further amplification in an amplifier '7, may be fed to the antenna 8.

v The corresponding carrier has the frequency h2+h1. This frequency may be produced in that in'a modulator 9 the frequency derived from generator 16 is brought to modulate with the frequency hl derived from generator 3. What is delivered from modulator 9 is a-frequency mixture consisting of hZ-hl, h2, h2+h1. Now, this frequency mixture is passed through a band filter 10 whose fundamental frequencies lie closely above and below hZ-l-hl. Of the three frequencies fed into the band filter 10, as will thus be seen, on1y the frequencyh2+h1 is passed. Optionally after further amplification in an amplifier 11 to the requisite intensity, it is fed to the aerial 12. Y

Since in the presence of considerable (close) coupling of the aerials 8 and 12, there would ocour a mutual overmodulation of the amplifiers 7 and 11, it will be. necessary to balance out the two antenna: in reference to each other. This is shown in Fig. 1 by the inductance 13 uniting the antenna terminals of both transmitters.

For the purpose of neutralizing two aerials a great many diflierent ways and means are feasible. Fig. 2 illustrates the method employed also in Fig. 1. Two antenna: 8 and 12 are fed from the transmitters 7 and 11 by Way of the coupling coils 2G and 21. The capacitive coupling of both antenna is represented by the condensers 30 infrom the antenna 8 to the antenna 12,- in the presence of such potential as prevails across the terminals of coil 31, then the current flowing through aerial 8 is likely to set up a current inthe aerial 12. But'this current returns by way of the coil 33. and does notgo by way of the coupling coil 21 so that it will be unable to react upon the transmitter 11. The same thing holds true inversely respecting the action of transmitter 11 upon transmitter 7. In the case of Fig. 3 neutralization of aerials 8 and 12 is accomplished by that the antenna by the aid of two coils 24 and 23 in series with their coupler coils 20 and 21 are so coupled that the current flowing through the aerial 8 by way of coils 24 and 23 will just set up an electromotive in the antenna opposite to that of the capacitive coupling acting through the space coupling 30. The coupling 24, 23, is so adjusted that a current in the antenna 8 as a result of this coupling drives a current through coil 21 which is of the same size, though of opposite sign, as the current set up by the antenna 8 through the space capacity 30 in the coupling coil 20. A potential originating from transmitter 7, as will thus be seen, will fail to force a current through the coupler coil 21 and therefore produces no action upon the transmitter 11. The same thing, only inversely, holds good for the effect of the transmitter 11 upon the transmitter 7.

To be sure, in both instances the current induced by one of the antennae in the sender coupling coil of the other antenna is reduced to zero value. But in the antenna themselves there remains a residual current which affects the uniform radiation of the sending aerial and imparts to it a certain directional efiect; In case this should be especially undesirable and if a particularly small distance between both antennae is desired, then an arrangement as-shown in Fig. 4 could be suitably used. Inthis case the antenna: 8 and 12 are not only neutralized (uncoupled) by the aid of the inductance 31 uniting the coupler coils 20 and 21, but in addition by other coils 32 and 33 uniting suitably selected points of the antenna. It is possible as a result to return such current as may have been supplied by way of from the upward point. Consequently the current flowing in the induced antenna will everywhere assume but small values and the directive actions thereof will be but inappreciable.

I claim. V t

1. The method of signalling which comprises producing high frequency oscillations, producing signal oscillations, modulating said high frequency oscillations with said signal oscillations, separating a side band from said modulated oscillations, producing other high frequency oscillations, combining said other high frequency oscillations with said side band, amplifying said resultant frequencies, combining said last named high frequency oscillations with said firstnamed high frequency oscillations, and amplifying the resultant oscillations. I

'2. The method ofsignalling which comprises producing high frequency oscillations, producing signal oscillations, modulating said high frequency oscillations with said signal oscillations, separating a side band from said modulated oscillations, producing other high frequency oscillations, combining said other high frequency oscillations and said sideband, combining said first and other high frequency oscillations to produce a carrier wave, amplifying the energy resulting from combining said other high fre quency oscillations and said side band, amplifying said carrier wave and transmitting energy resulting from combining said other high fre-- quency oscillations and said side band and said carrier wave separately.

3. The method of signalling which comprises, producing high frequency oscillations, modulating said high frequency oscillations at signal fre--- quency, separating a side band from said modulated oscillations, producing other high frequency oscillations, combining said other high frequency oscillations with said side band, amplifying the energy resulting from said combination, combining said last named high frequency oscillations with said first named high frequency oscillations to produce a new carrier, amplifying said new carrier, separately radiating the amplified frequencies resulting from the combination of said other high frequency oscillations and said side band and the amplified carrier oscillations resulting from the combined high frequency oscillations, and compensating the eifect of the amplified energy resulting from combining the said other high frequency oscillations and the side band on the amplified carrier resulting from the combination of the two produced oscillations.

4. A'signalling circuit comprising, a generator of high frequency oscillations, a modulating cirfirst named high frequency generator and said second named high frequency generator, a filter circuit connected with said third named modulator, an amplifier connected with said filter circuit and radiating means connected with said amplifier.

5. A circuit arrangement as recited in claim 4 in which reactances are coupled between said radiating means to permit flow of compensating energy therebetween to eliminate the effect of energy radiated therebetween on said circuits.

6. Signalling means comprising, an oscillation generator, a circuit for modulating oscillations from said generator at signal frequency, a filter circuit connected with said last named circuit for separating a single side band from the modulated energy, a second oscillation generator, a modulating circuit connected on the one hand with said second named oscillation generator-and onthe other hand with said side band filter, a filter connected with said second named modulating circuit to separate from the energy therein a single side band, radiating means connected with said last named filter, a third modulator circuit connected withboth of said oscillators to combine the energy therefrom, a third filter circuit connected with said third named modulator to separate therefrom a component of the resultant energy, and separate radiating means connected with said third named filter.

, 7. A signalling circuit as recited in claim 6 in which a'plurality of reactances of different character are coupled between said aerials.

WILHELM RUNGE.

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