US1795858A - Radio transmission system - Google Patents

Description

R. A. HEISING 5,858

RADIO TRANSMISSION SYSTEM Filed April 29, 1924 myeflior: fiaymaMA HHS/by Patented Mar. 19, 1931 innran stares earner QFFICE I nnrivronn A. nnrsrncr; or MILLBURN, new anRsnY, AssreNoR T WESTERN ELECTRIC ooMrAnY, moonrona'rnn, on NEW YORK, N, Y., A conronerron or new YORK 'nenro rnensnrssion SYSTEM Application filed. April 29,

This invention relates to radio transmission systems and more particularly to modulating systems wherein the generationof' un desired wave components is substantially prevented. r v

An object of this invention is to produce a completely modulated wave'and to substantially prevent the generation of undesired components therein. e

- Another object is to reduce the energy consumed in a modulating system when no signals are being transmitted thereby.

An additional object is to produce a modulated Wave having'side band components only which correctly represent the modulating wave. i i A feature of the invention relates to means for the transmission of radio signals and for preventing loss of'ene'rgy when no signals are transmitted. I

=Another feature concerns .the arrange ment wherein complete modulation of high frequency waves is effected without the introduction of components resulting from distortion and whereby the modulated waves may be delivered directly to an antenna. A further feature isan" arrangement of space discharge tubes for causing interaction betweencarrier and signal waves and for suppressing the unmodulated components of carrier frequency resulting therefrom by shifting the phase of the carrier waves supplied to the antenna during alternate; half cycles of signal waves. 1

Broadly,'this invention comprises a source of signal waves controlling an arrangement of space-discharge tubes for amplifyingthe signal waves, which arrangement is coupled to a source of high-power high-frequency waves whereby they are combined with the signal waves directly in a load-circuit such as an antenna or a wire line. The space discharge tubes may be so adjusted as to producecomplete modulation and are preferably connected in the so-called push-pull arrangement for preventing the production of undesired components tending-to produce dis-v tortion of the signals. The invention also includes facilities for preventing'the transmission of unmodulated components of carrier 1924. Serial No. 709,737.

frequency and for reducing the energy consumed during the periods when no signals are being transmitted. As a meansof'effecting carrier suppression the signal waves are arranged to control the source of space current for a high frequency amplifier in such a manner that during alternate 'halfcycles of the slgnal waves the phase of carrier waves in the amplifier circuits is shifted to reduce thelr efiective amplitude to any desired degree or even to Zero. The signal waves also actto stop the flow of space current in the high frequency amplifier so that no high frequency waves may be transmitted therefrom when no signal waves are supplied thereto.

To reduce the consumption of energy in the signal amplifier when no signals are transmitted a negative potential is supplied to the control electrodes thereof suflicient to prevent the flow of space current.

In the drawings: Fig. 1 illustrates a radio transmitting system for supplying high-power completely modulated waves directly to an antenna with-'- cate similar parts.

The modification shown in Fig. 1 comprises a source of signals 10, here shown as a microphone transmitter, coupled to a pushpull space discharge amplifier having its output circuit coupled to the output circuit of a space discharge oscillator by means of an ad ustable auto transformer25. The

oscillator 30 is coupled to an antenna 40. The

source of signals 10 is connected in serieswith a battery 11 and the primary winding of a transformer 12, the secondary winding-of whichiis differentially connected to the baianced input circuits 18 and 14 connected re-v spectively to the control electrodes of space discharge tubes 15 and 16. The midpoint of the secondary winding is connected in series with a grid polarizing battery 17 in common to the cathodes of tubes 15 and 16. circuits 18 and 19 are connected respectively to the anodes of tubes 15 and 16, and include separate portions of the winding of adjustable transformer 25. A common path between a mid tap of transformer and the cathodes oftubes 15 and 16includes a source of space current 26, here shownas a battery.

The oscillator includes a space discharge tube 31, and an anode circuit thereof which is connected to an adjustable tap of transformer 25. The anode circuit may be traced as-follows: anode of tube 31, high frequency choke coil 32, a portion of the winding of transformer 25,- battery 26 to the cathode of tube13'1.

The highfrequencychoke coil 32 is pro vided in thiscircuitin order to prevent high frequency waves from flowing in the space current circuit-of the amplifier 20 and the oscillator 30. Battery 26 it is seen serves tosupply space current to all the tubes of the system. Oscillator 30 includes in addition an input circuit-connected to the control electrodeand-cath-ode oftube 31 which may be traced'trom-this electrode to coil 33, leak resistance 36 shunted by blocking conoenser to the cathode of tube 31'. The output circuit of-tube' 3'1 is'connected between its cathode and'anode'and includes coil 37 shunted by condenser 38" in series with a second condenser 39.

The input and output circuits of oscillator 30- are'associated in energy transfer relation whereby continuous high frequency oscillations-are established in the circuit. Antenna 40 is directly associated with the oscillator 3O by thecoupling between coils 37 and 42, 33 and M respectively. The antennais connected-to ground in series with a condenser 41' and coils 4-2, l3 and 4e. Coil 43, which is adjustable within the coils 4:2 and la, in combination therewith, constitutes a variometerfortuningthe antenna circuit to the frequency of waves to be transmitted. The tuning of the antenna determines the frequency of oscillations. generated by oscillator 30.

Signalwaves from'source 10 are supplied to the input circuits of tubes 15 and 16 through transformer 12. rangement is such that when the waves from source 1O tend to reduce" the negative potential-on the control electrode of tube 15 they simultaneously tend to increase the negative potential'on the controlelectrode of tube 16. Thus,- am'plified signalwaves are repeated in theoutputcircuits of tubes 15 and 16 during alternate halfcycl'es of the impressed waves from source 10 ina manner well understood.

Battery 17 is provided to supply a suitable average potential on the control elec- Output.

The circuit a'rtrodes. This potential may be such that when no signal waves are supplied to the tube the space current therein is reduced in value or completely stopped.

Space current is supplied to tubes 15 and 16 by battery 26 connected to the anodes thereof through respective portions of the winding of transformer 25. Battery 26 is also arranged to supply space current to the tube 31'. The anodeof thistube is connected to an adjustable tap on'tra-nsfo'rmer 25. By adjustment of this transformer signal waves having the proper degree of amplification to periodically reduce the high frequency waves to zero amplitude, that is to produce complete modulation of waves generated byoscillator 30, are supplied to theanode circuitof tube 31. By virtue of the coupling between the input and output ,circuits'oI tube'31 highpower high-frequency waves are generated in the oscillator. These waves-are combined in the output circuit with signal wavesfrom amplifier 20 to produce a signalmodulated wave in a manner well understood.-- These modulated waves are supplied directly; to the antenna 40 at coil-l2 and the energy the'reofis raoiated into space.

Condenser 39 in the output circuit-oftube 31 prevent-stile fiowof space current in this circuit under the action ofbattery 26., Leak path 35, 36 is provided to allow the proper accumulation ofnegative charge on, the control electrode of tube 31.

There is illustrated-in Fig... 2- a radio trans mitting system comprising a source of signals 10, coupled to a push-pull amplifier 20 which in turn is coupled in tandem to a second push-pull amplifier supplied with energy from a source of high frequency' waves 60 and coupled to antenna 70. The amplifier 20' of this figure corresponds to the amplifier 20 of r Fig- 1 but in this-figure the output circuits 18* and 19: are connected. respectively through the primary winding of transformer 27 to a source of space current 29, here shown as a directcurrent generator;

The amplifier 50 comprises spacedischarge tubes- 51" and 52 having their anode circuits connected in balanced relation to the secondary winding of transformer 27 and inchidingchoke coils 53 and5t; The midpoint of the secondary winding'of transformer 27 is connected by a common lead'to the cathodes of tubes 51 and 52. The primary winding of transformer 55 is supplied with" highfrequency waves from a source and the secondary of this-transformer supplies'these wavestothe ba lanced input circuits of tubes 51 and 52connected between their respective control electrodes and cathodes: The midpoint of the secondary winding is connected through a grid polarizing battery 56 to the cathodesofthe tubes. 7

The amplifier 50' also comprisesbalanced output circuitsc'onnected respectively tothe a carrier frequency. The phase of the unmoduanodes of tubes 51 and 52 and including respectively the condensers 57 and 58 having their adjacent terminals connected to one terminal of a coil 59, the opposite terminal of which is connected to the cathodes of the tubes through switches 28. An antenna is connected to ground in series with coil 71, which is coupled to coil 59. By operating switches 28 the filter 61 may be connected in the common branch of the output circuit of amplifier 50.

Source 10 and amplifier 20 are arranged to supply positive pulses corresponding to alter nate half cycles of amplified signal waves to the respective anode circuits of tubes 51 and 52 through transformer 27. No other source of anode potential is provided for the tubes 51 and 52, consequently when no signals are supplied fro-m source 10, no space current flows in these tubes. Source 60 supplies high frequency Waves through transformer 55 to the inputcircuits of tubes 51 and 52. Hence, when signal waves are supplied to the anode circuits, the high frequency waves corre-' sponding to those produced by source 60 are repeated in the anode circuits of the tubes and modulated in amplitude in accordance with the signal waves. During positive half cycles of signal waves, high frequency waves are repeated and modulated in the output circuit, of one tube, whereasduring the negative half cycles the high frequency waves are modulated in the output circuit of the opposite tube. i

The waves produced in the output circuits are supplied through coil 59 connected in common thereto whereby the waves from one output circuit are in out of phase relation with Waves of the opposite output circuit. Thus, there appear in the antenna circuit coupled to the coil 59, side band frequencies without any unmodulated component of the lated component is reversed during each half cycle of the signal wave, this being a characteristic feature of this type of carrier suppression system.

To suppress one side band the filter 61 may be connected by operating switches 28, as already described. This filter is designed to have high input impedance to the undesired side band and low input impedance to the desired side band. The input impedance referred to is the impedance offered by the filter in the path connecting switches 28 when they are thrown to put filter 61 in circuit.

' The transmission band of this filter will be the undesired side band. Energy of the Wave components of the undesired side band is transmitted through the filter and dissipated in the resistance 61a.

Choke coils 53 and 54: are provided to prevent the passage ofhigh frequency currents,

through the windings of transformer 27.

Condensers 57 and 58 prevent the flow of the unidirectional or low frequency current through the output circuits of tubes 51 and 52. p 1

The potential on the control-electrodes of tubes 15 and 16 may be adjusted by means of battery 17 to a value such that no space desired side band'is suppressed. The waves 1 within the desired side band are transmitted by the filter to the transformer 590; and 'impressed upon the antenna circuit.

The filters Gland 63 are of the well known band-pass type or may be'of any other type having similar transmission characteristics. This invention has been illustrated in certain specific embodiments but it is intended to be limited only by the scope of the appended claims. v c

-VVhat is claimed is:'

1. In combination, a plurality-of pairs of space discharge amplifiers, one pair having their output circuits electrically coupled-to the output circuits of the other pair, means for supplying signal wavesto one pair of said amplifiers, means for supplying high frequency waves to another pair of said amplifiers, and means for producing a fiow of space current in one pair of said amplifiers, only when signal waves are supplied to the other pair of said amplifiers.

2. In a radiant energy signaling system, a space discharge amplifier having input and output circuits, said input circuit being supplied with waves of high frequency, a source of signals, a push-pull space discharge amplifier supplied therewith, said last named amplifier being coupled to the output circuit of said first named amplifier, means for causing a flow of space current in the output circuit of said first named amplifier only during the time when signal waves are supplied to said second named amplifier, and means for shifting the phase of wave components of high frequency in the output circuit of said first named amplifier whereby the unmodulated component of said high frequency waves is substantially suppressed in said output circuit.

band frequency with no unmodulated' com- 3. In a radiant energy signaling system, 7

ponent of the carrier frequency waves "in the output circuit of said second amplifier, a load circuit connected directly to said output circuit, and means included-in said out- I put circuit for suppressing certain of said Waves of side band frequency.

4. In a radiant energy signaling. system, a source of signal Waves, a source of carrier Waves, a space discharge modulator supplied with said Waves whereby side bands are produced, an output circuit for said modulator traversed by said side bands, and a filter in said output circuit, said filter having high impedance to the undesired side band, the transmission band of said filter including said undesired side band.

5. In a radiant energy signaling system, a source of signal Waves, a source of carrier Waves, a space discharge modulator having its input circuit connected to said source of carrier Waves and its output circuit connected to said source of signal Waves, whereby Waves of side band frequencies are produced in said output circuit, and a filter in said output circuit having high impedance to an undesired side band, the transmission band of said filter including an undesired side band said filter having a resistance connected across its terminals remote from said output circuit.

In Witness whereof, I hereuntosubscribe my name this 28th day of April, A. D. 1924:.

RAYMOND A. HEISING.

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