US1732741A - Duplex radio transmission system - Google Patents

Description

' Patented a.- 22,1929

UNITED STATES PATENT OFFICE FRANK CONRAD, 0F PITTSBURGH, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSE ELECTRIC d, MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA DUPLEX RADIO TRANSMISSION SYSTEH Application filed ma 4,

simultaneous transmission of two messagesat substantially a single transmission frequency.

Another object of my invention is to providea radio signalling system in which signals are transmitted simultaneously by modulation of the amplitude of oscillation and by modulation of the frequency of oscillation.

It has been customary to transmit voice frequency signals by means of modulation devices, operating with oscillation generators,

which vary the amplitude of oscillation in accordance with the voice frequency vibrations. With other systems it has been customary to transmit code signals by varying the frequency of oscillation in accordance with the code signals. It has, however, been considered that such systems were mutually exclusive and that a system embodying one principle could not embody the other.

I have found that, at certain frequencies,

it becomes possible to operate both systems simultaneously from a single high-frequency generator without interference therebetween. It is possible to combine the two systems with an oscillation frequency of about 1500 kilocycles. I find that such operation is even more satisfactory at frequencies above 3000 kilocycles. By this means, I am enabled to transmit two kinds of signals simultaneously from a single oscillation generator without 4 interference therebetween.

Other objects and structural details of my invention will become apparent from the following description, when read in connection with the accompanying drawing wherein the single figure is a diagrammatic representa- 1925. semi m). 21,024. M

6 and the condenser 7. A second triode 9 has associated therewith, a transformer 11 and a telephonetransmitter 12. y

The anodes of the triodes 5 and 9 are connected in parallel to a generator 14 through a choke coil or inductance 15. The cathodes of the triodes 5 and!) are supplied by a gcnerator 16, the other terminal of the generator 14 being connected to the other side of the cathode circuit.

A small variable reactor, such as a condenser 17, has one plate which is attached to the arm 18 of a relay 19. The coil of the relay 19 is connected to a battery 21 and key 22. The plates of the condenser 17 are connected by conductors 23 and 24 across a portion of the turns of the inductance 6.

The oscillating circuit of the generator is connected to the radiator by a conductor 25 and an inductance 26. a y

In the operation of my device, the amplitude of oscillations generated by the generator triode 5 is controlled in any well-known way by the amount of current taken by'the modulator triode 9, which in turn is controlled by sound waves acting through the microphone 12 and the transformer 11 upon the grid of the triode 9. Voice signals impinging upon the microphone 12 thus vary the amplitude ofthe oscillations generated by the triode 5 and, therefore, the amplitude of the oscillations radiated from the aerial 1. These oscillations may then be received by a non-oscillating receiving system.

Simultaneously with the modulation of the amplitude of the oscillations generated by the triode 5, the frequency of the said oscillations maybe varied by movements of one of the plates of the condenser 17, which has the effect of changing slightly the effective capacigenerator.

ing of the resonant circuits of the receiving apparatus. The variation of the condenser 17 and thereby the variation in frequency is controlled by movements of the key 22.

A second radio receiving apparatus may be rovided in which the receiving circuit is iept in oscillation by an oscillator at a frequency different from thefrequency of generation of the sending device. The usual het erodyne system may b'e-used for this pur- .pose. This frequency may be the same as the frequency of generation of the sending apparatus when the sending key is up, thereby giving a zero beat frequency. Actuation of the key changes the condenser value and thus changes the frequency of the sending apparatus to a value which produces a beat frequency within the audible range. The listener will, therefore, hear a beat note which corresponds to the code signals formed by the key 22.

In simultaneous operation of the two signalling systems, the change in frequency necessary for the code signalling is insufiicient to produce a perceptible change at the ordinaryreceiving apparatus. Also, the carrier wave with which the local oscillator at the code receiving station is heterodyned is so much greater than the modulated components that the speech modulations are substantially imperceptible and the heterodyne Wave only is brought to theoperators attention.

By this means, I am enabled to provide a. system having a single generator which is capable of simultaneous 'voice and code signalling at substantially a single frequency.

lVhile I have shown but one embodiment of my invention it is capable of various modifications therefrom without departing from the spirit thereof. I desire, therefore, that my invention shall be limited only by the appended claim and by the prior art.

I 'claim as my invention:

A duplex radio signalling system comprising a sending set and at least two receiving sets, one of which is an ordinary receiving set, said sending set including means to generate and radiate high-frequency oscillations, means to modulate the amplitude thereof in accordance with one signal'and means to modulate the frequency thereof in accordance with another signal, the degree of change of frequenc produced by said lastmentioned modulatlon means being so small a percentage of said high frequency that the set and will not interfere with the reception of the first-named signal by the ordinary receiving set.

In testimony whereof, I have hereunto subscribed my name this 20th dayof April,

FRANK CONRAD.

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