US2047622A - Duplex radio transmitter - Google Patents

Description

July 14, 1936. J EVANS 2,047,622

DUPLEX RADIO TRANSMITTER I Filed Aug. 11, 1934 \r m H g Q N N a m E a 5 QI' 3 L2 1 7'0 MODULATOR INVEN'I'OR John Evans a'r'romvgy Patented July 14, 1936 UNIT ATNT it:

DUPLEX RADHO TRANSMITTER John Evans, Riverside,

N. 3., assignor, by mesne Application August 11,

5 Claims.

This invention relates to duplex radio transmitters and more particularly to a device embodying means to facilitate the changing over of resonant networks so that the transmitter may be employed on either one of two frequency bands, one band being in the ultrahigh frequency range and the other of relatively low frequency.

An object of my invention is to provide a duplex radio transmitter in which either of two frequency bands may be selected to the exclusion of the other, and when so selected, the transmitter may be operated without appreciabie loss of energy.

It is known that for transmission of an ultrahigh frequency carrier wave, a push-pull arrangement of the oscillator tubes and of the amplifier tubes provides the optimum conditions of operation. On the other hand, when low frequencies are to be transmitted, the symmetrical circuits which are provided, may best be operated in parallel. V

In order that the tubes and certain portions of the oscillator and amplifier networks of my invention may be selectively adapted to operate either at ultrahigh frequency or at the lower frequency, I have provided certain simple switching arrangements and circuit connections which can be handled with a minimum of effort.

The objects and advantages of my invention will best be understood upon reference to the following detailed description when read in connection with the accompanying drawing in which the sole figure thereof represents a circuit dia-- gram of a preferred embodiment.

Referring to the drawing, I show a pair of electron discharge devices I which may either be ordinary triodes or tubes of any other suitable type. The cathodes 2 of these tubes have been shown as of the indirectly heated type. Directly heated filament cathodes may be used instead, if preferred. The grids 3 are connected to a resonant loop 4, the tuning of which may be accomplished by means of variable capacitors 5. The loop 4 cooperates with the tubes I to operate the same in a push-pull manner to generate an ultrahigh frequency. The output circuit for these tubes is also made resonant by means of the inductive loop 6 and the tuning condensers l. Anode potential is supplied to the plates of the tubes I from any suitable source as indicated by the plus and minus signs at 8. The output energy of the oscillator may be transferred through the coupling condensers 9 to a resonant input network including the grids of a pair of electron discharge tubes Ill. The tuning of the input circuit for the tubes may be adjusted to a desired value as by 1934, Serial No. 739,436

means of the inductances l. The output circuits of the tubes Ill may also be tuned as by means of the inductive loop I2 and the tuning condensers I3.

The tubes IE and the circuit connections thereto constitute one stage of amplification. A second stage of amplification, like the first, may also be provided, constituting the tubes M. The output energy from the amplifier tubes i l may be inductively transferred to a work-circuit including the inductive loop l5 and the adjustable capacitors iii. If desired, one of the capacitors it may be connected to a short-wave antenna and the other to a counterpoise. If, however, it

is desired to employ a dipole antenna, then the condensers It may be connected thereto in any suitable manner well understood by those skilled in the art.

The oscillator with its two stages of amplification, as hereinbefore described, may be supplemented by additional tuned circuits for occasional use so as to enable the transmitter to operate at a comparatively low frequency. The additional networks comprise, in the oscillator stage, a tuned tank circuit having an inductance I? and a variable capacitor l8; and, for each of the two stages of amplification, a tank circuit comprising an inductance l9 and variable capacitor 2%. When these tank circuits are connected into the oscillator-amplifier network, the various pairs of electron discharge tubes are caused to operate in parallel. For the low frequency operation, the inductive loops 4, 6, l2 and l 5 provide paths of negligible inductive value. The values of the condensers 5, 1 and I3 are such that they offer a high impedance to low frequency currents. It will be seen, therefore, that for all practical purposes, the resonant networks, which are provided for the ultrahigh frequency service, may be ignored when connecting in the tank circuits for use in low frequency transmission.

By a simple switching operation, the various pairs of electron discharge tubes may be operated either push-pull or in parallel. For this purpose I provide preferably a relay 2!, the operating circuit for which may include a battery 22 and the push-button switch 23-24. By depressing the push-button 24, the relay becomes energized so as to open the short-circuiting contacts 25 and 26 and also to close pairs of contacts 21, thus grounding two tuning condensers 28. The character of this switching operation is such that the tank circuits, including inductances I1 and I9 and tuning condensers l8 and 20, may be operably placed in circuit with the oscillator and amplifier tubes thereby causing these tubes to operate in a parallel manner. The grounding of the condensers 28, each on one side thereof, completes the arrangement for making the oscillator circuit resonate at the desired low frequency.

When it is desired to operate my transmitter at low frequency I employ a tank circuit 33 connected with the output circuit from the tubes [4 through the loop l2. The output from a modulator may be impressed upon this tank circuit 33. Coupled to the inductance 29 of the tank circuit is a coil 30 on which the modulated output energy may be impressed. This coil 30 is in circuit with a variable inductance 3i having a connection to a low frequency antenna. Neutralizing condensers 32 are provided between stages of the low frequency tank circuits of the amplifier stages.

From the foregoing description the advantages of my simple switching arrangement will readily be seen. The transmitter, at times, may be operated at ultrahigh frequency when the pushbutton 24 is not depressed. The conditions then obtained provide for push-pull operation of the various pairs of electron discharge tubes. At other times, the transmitter may be operated at a comparatively low frequency by depressing the push-button 24 and providing for the introduction into the operable portion of the transmitter network of the several low frequency tank circuits. If desired, the switching arrangements may be manually operated instead of operating the same by means of the relay 2|.

Although I have described a preferred embodiment of my invention, it will be readily understood by those skilled in the art that modifications may be made without departing from the spirit thereof. I intend, therefore, that no limitations shall be imposed except as are neces sitated by the prior art and by the scope of the appended claims.

I claim as my invention:

1. In a radio transmitter, an ultra-high frequency oscillator and amplifier having tuned input and output circuits and tuned interstage coupling impedances, a pair of electron discharge tubes connected for push-pull operation in the oscillation generator stage, other pairs of electron discharge tubes likewise connected in the amplifier stages, a set of relatively low frequency tank-circuits and additional reactances at times cooperable with said discharge tubes for generating and amplifying relatively low frequency oscillations, means for at such times causing respective pairs of said tubes to operate in parallel, and means for short-circuiting at least two of said tank circuits and for disabling said additional reactances when said transmitter is t obe rendered operable at an ultra-high frequency.

2. Apparatus in accordance with claim 1 characterized in that said short-circuiting and disabling means is relay operated.

3. In combination, a plurality of sets of electron discharge tubes arranged in stage-by-stage pairs for the generation and amplification of radio frequency oscillations, an ultra-high frequency oscillator network into which the first pair of said tubes is connected, amplifier networks into which succeeding pairs of tubes are connected, means for energizing said tubes in a push-pull manner and for controlling the operation of said networks for at times producing a modulated ultra-high frequency signal, and means including additional resonant circuits connectible stage-by-stage to said pairs of tubes for producing a relatively low-frequency signal therein, the last said means being operable further to cause the respective tubes of each pair to. function in parallel.

4. A device in accordance with claim 3 having a relay-controlled switch for rendering the last said means operable.

5. In a duplex radio system, a generating and amplifying network comprising a plurality of electron tubes, circuit means connecting said tubes at one time in push-pull relation and at another time in parallel-feed relation, tuning means permanently connected in said network and adapted to render the same resonant at an ultra-high frequency when said tubes are in pushpull relation, second tuning means for rendering said network resonant to a relatively lower frequency and adapted to be connected into said network only when said tubes are in parallelfeed relation, said first mentioned tuning means being so permanently connected in said network as to produce negligible electrical efiect when said tubes are in parallel-feed relation, and. switching means for shifting said network from one frequency to the other.

JOHN EVANS.

Images