US2053014A - Wireless transmission system - Google Patents

Description

Sept-'1, 1936. G. w. WALTON WIRELESS TRANSMISSION SYSTEM Filed April 12, 1933 Patented Sept. 1, 1936 UETE STTES WIRELESS TRANSMISSION SYSTEM George William Walton, London, England Application April 12, 1933, Serial No. 665,818 In Great Britain April 23, 1932 3 Claims.

This invention relates to wireless transmission systems and has for its object the production of a system the operation of which will cause the minimum interference in a receiver which is not tuned to the transmission.

Hitherto in wireless transmission systems it has been the practice to modulate the amplitude of a carrier oscillation in accordance with the signal to be transmitted, and this results in the production of side bands. Objectionable interference'is often caused by these side bands in a receiver not tuned to the transmission. According to this invention a double transmission is simultaneously effected, that is to say .two carrier oscillations of the same frequency but having a phase displacement relatively to one another are simultaneously modulated by the signals which it is desired to transmit, and these two transmissions are simultaneously received by a receiver tuned to the transmission. Subject to certain relations between the two carrier oscillations and the modulations of those carriers hereinafter more particularly described, the side bands of the transmission are ineffective at their own frequencies due to the opposition of the side bands of one carrier oscillation to the side bands of the other carrier oscillation.

In order that the invention shall be more clearly understood, one form of transmission will be more particularly described with reference to the accompanying drawing, it being of course understood that the invention is not limited to the particular arrangement and apparatus described.

In the drawing, Fig. 1 is a circuit diagram of a Wireless transmitter according to the invention,

Fig. 2 is a circuit diagram of a receiver adapted for use with the transmission according to this invention and Figs. 3 and 4 are vector diagrams illustrative of the present invention.

Referring to Fig. 1, an oscillation generator I adapted to generate oscillations of a desired carrier frequency is coupled by a transformer 2 to the grid circuits of two transmitter valves 3 and 4 arranged in push-pull relation. The anodes of the valves 3 and 4 are connected through condensers l and 8 respectively to separate transmitting antennae 9 and Ill. The anodes of valves 3 and 4 are also connected through tuned circuits 5 and 6 to the anodes of two modulator valves I3 and I4, the latter anodes being also connected through choke coils II and I2 respectively to the positive terminal of a source of high tension (not shown), the negative terminal of which is earthed. The grid circuits of the modulator valves I3 and M are connected to the ends of the secondary winding of a transformer I5 the centre point of which is earthed through a suitable grid bias battery IS. A microphone I1 is coupled through an amplifier indicated by l8 t0 the primary Winding of the transformer I5. A suitable biasing battery I9 is also provided for the valves 3 and i and the negative terminal of this battery is connected through a resistance 10 29 to the grid of the valve 3 and through a condenser 2I to the grid of the valve 4. Either or both of the elements 20 and 2| may be variable and by adjusting their relative values the phase difierence between the carrier oscillations in 15 tuned circuits 5 and 6 can be adjusted. The phase diiference may be made about and. should preferably not exceed this.

The signal voltages from the microphone I! which are fed to the grids of valves I3 and I4 will clearly be phase displaced relatively to one another. The amplitudes of the signal oscillations in the anode circuits of the valves I3 and I4 should preferably be made substantially exactly equal and opposite and this can be done by adjusting the rheostats 22 and 23 which are arranged in the filament heating circuits of the valves. A suitable source of filament current is connected to terminals 24.

The nature of the signals transmitted by the circuit of Fig. 1 will best be understood by reference to Figs. 3 and 4. The two carriers which are 90 phase displaced relatively to one another, when unmodulated, are represented by vectors A and B in full lines. When they are modulated, the vector A reaches value 0 when vector B reaches value D and vector A is at E when B is at F. Assuming that the modulation causes the vectors A and B to vary between C and E and D and F respectively, the resultant energy transmitted from both aerials will vary between the position G, through position H corresponding to zero modulation to position J. It will be noted that the resultant vector always lies between parallels K and L.

The resultant vector can be resolved into two components, one a vector H of constant length and direction and the other a vector M varying between the full line value through zero length to the dotted line value. The only variable component thus remains in the line L and produces no net effect upon a receiver of ordinary type.

A manner in which such a transmission can be received will be appreciated from an inspection of Fig. 4, where like vectors have the same references as in Fig. 3. If there were combined with the received signal a vector such as N, this vector N would have a component P neutralizing vector H and a component Q making the variations of M all in one sense, namely to the right in the figure. Even if the vector component Q were shorter than shown it would introduce sufficient asymmetry for the signals to be heard but it would operate less eificiently.

The receiver shown in Fig. 2 isadapted. to do this. A tuned circuit 25 is connected between the receiving antennae 26 and earth and this circuit is tuned to the incoming carrier frequency. The" circuit is connected through :a condenser 2'l shunted by a grid leak 28 to thegrid circuit of a thermionic valve 29 acting as a detector. The anode circuit of the valve 29 is coup-leda-bya transformer 39 to a low frequency amplifyingvalve 3| which is coupled through a transformeru32. to a loudspeaker 33. The anode of valve 29 is connectednthrough a condenser. 34 .to the grid of a phase changingvalve 35,.a resistance 36 being connected between the gridsand .cathode of this valve. may be variable. Theanode circuit of the valve 35 contains a coil 37 variably coupled to the tuned circuit 25. A source of'voltage 38 is provided for the three valves29', 3| and35.

a The'circuiti'fromthe tuned ci'rcuit25 through :valve29, transformer 30, valve 3|, transformer 32 to'zloudspeakeni-iSin a conventional receiving circuit. In addition to this, however, there is the valve 35 and itsassociated circuits. By adjusting the condenser. or'resistance' SB, or both, the phaseoiztheoscillations fed back by coil 31 can bei'adjusted. f If, for example, the phase'is made such thatitheoscillation fedby coil'3l into circuit 25 are represented by the vector R in Fig. 4, then' these retroactive oscillations twill tend to drag :the original oscillations; represented by vectOra'I-I, into step'with them. Any tendency for vectorI-Ito rotate to the right will make R move to the rightahso. Finally the vector R will tend to take up a-position N in which the vector H is balanced out. The modulations then become audiblesin the -;loudspeaker 33.

*Inany case it will'be observed that so long as thevector R-has a component in the direction Q (Fig. 4), that is to say so long as the-vector R.- is phase displaced relatively to vector H-by an angle other than 180, itscomponent in'the direction Eithenor both of the elements 34 and 3E Q will make the varying vector M asymmetrical and so make the signals audible. The most efficient condition is, however, that in which the vector added is as shown at N.

I claim:

1. A transmission system comprising means for generating two carrier oscillations of the same frequency but displaced in phase relatively to one another, a source of electricalvariations corresponding to intelligenceto be transmitted, means for deriving from said variations two sets of elec- 3 itrical variations of like wave form but phase displaced relatively to one another, means for ami plitude'modulating one of said carrier oscillations with oneof-saicl sets of variations and for simultaneously amplitude modulating the other of said carrieroscillationsawith the other of said sets of variations and tuned radiating means for sepa- I can'ieroscillations.

3i=A transmission system-comprising means for generating two. carriercscillations of the same frequency but displaced in: phase by substantially" relatively to oneanother, a source of electrical variaitionscorresponding to intelligence to be transmitted, meansfor deriving from said variations twoirsets .of electrical variations of like wave? form but phase displaced by substantially relatively to one another, means for amplitude; modulating :one of said carriersosc'illations withone of said sets of variations and for simultaneously amplitude modulating the other of said carrier oscillations with the other. of said sets of variationszandtuned radiating means for. separately transmitting-said carrier oscillations.

1 .GEORGE WILLIAM WALTON.

Images