US2025129A - High frequency translating circuit - Google Patents

Description

Dec. 24, W SCH FER HIGH FREQUENCY TRANSLATING CIRCUIT Original Filed Nov. 11, 1926 REj/J 774mg 02 Moms c011 lNVENTOR WALTER SCHAFFER BY v f I M ATTORNEY Patented Dec. 24, 1935 UNITED STATES PATENT OFFICE HIGH FREQUENCY TRANSLATING CIRCUIT Delaware Original application November 11, 1926, Serial No.

Patent No. 1,956,964, dated May 1,

1934. Divided and this application February 23, 1932, Serial No. 594,591. In Germany November 26, 1925 8 Claims.

My invention relates to a connection for the operation of high-frequency amplification systems for receiving and sending electric waves, and it is an object of my invention to eliminate the obnoxious tendency of the tube amplifiers to become self-excited, and is a division of my copending application, Serial No. 147,676, filed November 11, 1926, which resulted in U. S. Patent #1,956,964, May 1, 1934.

To this end, I arrange intermediate the anode and the cathode of a tube a series unit comprising a capacity and a self-inductance which unit is tuned to the operating frequency of the system and the voltage induced in this unit will be a maximum when the voltage in the tube is a minimum. The induced voltage may be transmitted to the grid of the following tube through conductive, capacitative or inductive coupling, and, if desired, may be transformed upward before being thus transmitted.

The undesirable self-induction of the tubes is due to a comparatively high voltage between the anode and the cathode of the tube which acts on the grid past the capacity intermediate the anode and the grid so that undesired back-coupling and oscillations are generated.

This may be counteracted by the known neutrodyne connection by which the back-coupling effect of the voltage between the anode and the cathode of the tube is balanced, but in my invention the voltage is not balanced but eliminated.

A tube connected and operated as above may be incorporated in a relay circuit as described and broadly claimed in said application No. 147,676, filed Nov. 11, 1926, of which application this application is a division or may be incorporated in a transmitter as set forth and claimed in the present application.

When the tube connected and operated, as indicated above, is used as a generator to produce constant frequency oscillations which are fed to amplifiers etc., for transmission, the following circuits include means for eliminating harmonics from being radiated. The combined apparatus results in an arrangement for the e-fficient production and transmission of oscillations free of harmonics or superposed oscillations.

In the drawing three diagrams of connections according to my invention are illustrated by Way of example.

Fig. 1 is a diagram of a receiver,

Fig. 2 is a similar diagram showing a backcoupling in series with the series unit,

Fig. 3 is a diagram of a sender.

Figure 4 illustrates diagrammatically the mannor in which the oscillations may be modulated at signal frequency by a capacitive microphone.

Referring now to Fig. 1, l is an antenna, 2 is a tunable grid circuit, 3 is a high-frequency tube amplifier in the grid circuit 2 of which voltage is 5 induced by the antenna 1, 4 is an anode battery, 5 is a radio frequency by-pass condenser connected in parallel to said battery, 6 is an ohmic series resistance through which the battery 4 is connected with the anode circuit at I3, 1 is a rotating plate condenser, 8 is a self-inductance, 9 is a battery supplying the grid voltage for the following valve 3', and I1! is a radio frequency by-pass condenser in parallel to the battery. The parts I to it constitute the series unit which is connected to the grid circuit of the tube 3 at H and I2.

When the tube 3 is excited by the antenna l and the tuned grid circuit 2, alternating voltage will form at the ends of the self-inductance 8 and, since the condenser It; is without influence in this respect, intermediate the points I l and I2. The anode current of the tube 3 is direct current with superimposed alternating current. The direct current is blocked by the condenser I and fiows exclusively in the resistance 6 and the battery 4. The alternating current, on the other hand, is branched at E3, and its partial intensities are inversely proportional to the resistances oi. the branches 6, 4 and l, 6 with consideration of phase distortion, if any.

When the series unit is tuned to the operating frequency it constitutes a purely ohmic resistance, the total resistance between its ends being a minimum as the apparent impedance is ,zero. With the series unit tuned, especially if the ohmic series resistance 6 is high in proportion to the ohmic resistance of the series unit, the anode alternating current will flow principally in the unit and under these conditions the alternating voltage at the ends of the coil 8 will be a maximum and equal to IwL. At the same time, the alternating voltage between the anode and the cathode of the tube 3 is a minimum and is only determined by the value of the ohmic resistance in the series unit.

If the size of the self-inductance 8 were increased and that of the condenser l were reduced in order to maintain the tuned condition of the system, the voltage at the ends of the self-inductance 8 would increase unless accidentally the ohmic resistance of the self-inductance 8 had increased with its increase in size. The increase of the voltage may be prevented in practice without difiiculty. If the ohmic resistance of the ceding tube.

series unit is small enough and consequently the voltage between the cathode and the anode of the tube 3 is small, the tendency of undesired backcoupling and of self-oscillation of the tube 3 is also small with the waves employed.

The connection illustrated permits the transformation of an alternating voltage between the anode and the cathode of a tube by other means than those hitherto employed and the operation will be similar to that of a resonance transformer.

A current self-inductance which might increase the voltage between the anode and the cathode of the tube, is not shown in Fig. 1. If it were provided and the coupling from the self -inductance 8 to the grid of the following tube 3 were suitably modified, for instance inductive, the current selfinductance might be balanced by the condenser 'l.

The curve indicating the voltage at the ends of the self-inductance 8 as determined by the adjusting of the condenser 1 is very similar to a resonance curve the width of which is determined by the proportion of the resistance of the series unit to the value of the resistance in the circuit 5, 6.

The voltage at the points I I, I2 is transmitted I to the following tube 3' which, as shown, may be a rectifying tube amplifier. Obviously, another high-frequency amplifier tube might be provided in its stead, or a plurality of such amplifier tubes might be provided, with a rectifying amplifier or demodulator following the final stage in the cascaded radio frequency amplifier.

The operation as described will be performed so long as only voltage, and not power is transmitted at H, I2. If power were transmitted, ohmic resistance would be impressed on the series unit at l, 8, and would be wrong in principle. But, on the one hand, power can only be transmitted from the anode circuit of a tube if the voltage between the anode and the cathode were greater than corresponds to the ohmic resistance of the series unit at I, 8 for the power transmitted is invariably equal to the square of the anode current multiplied with the effective resistance transmitted to the anode circuit of the tube, and the anode alternating voltage will obviously increase with this resistance. n the other hand, the connection illustrated prevents the formation of a higher alternating voltage than corresponds to the power transmitted, because stray self-inductance, that is, self-inductance transmitted to the anode circuit, or prevailing capacity, may be balanced by setting the condenser l.

'For receivers, the transmission of effective resistance to the anode circuit, as indicated above is impossible because the grids of the following amplifier or rectifying tubes which operate the negative range, are excited without power. The cause why the high-frequency valves of the connections as employed hitherto, had a'tendency to self-exciting, was the formation of alternating voltage between the anode and the cathode of the tube which was not generated by transmitted effective resistance but was due to prevailing of the capacity. or inductance of the anode circuit. This is very probable because the power which the grid of a following tube consumes, even if the tube is not in the negative range, is so small in proportion to the power transmitted from the preceding valve that the effective resistance Would be only a very small percentage of the ohmic resistance in the anode circuit of the pre- But in fact, as shown, the ohmic resistance is not the cause of too high alternating anode voltage in the preceding tube but the prevailing of inductance or capacity in the anode circuit.

With the connection illustrated in Fig. 1 backcoupling may be provided at the first tube as 5 shown in Fig. 2. Referring now to that figure,

I4 is a back-coupling coil in series with series unit comprising the self-inductance" 8 and the condenser l. The back-coupling is a definite and purely inductive one because the stray self-in- 10 duction transmitted to the anode circuit from 2 and which might generate an additional inductive voltage, may be balanced by the condenser l of the series unit.

The system illustrated in Fig. 2 has a further advantage not found in the usual systems which results from the fact that M, l, 8 is tuned, which insures in this case that the maximum anode alternating current will occur in the branch 14,

This connection may also be employed for, selfexcited or separately excited senders. In selfexcited senders, a definite back-coupling is: reliably effected in which the anode alternating voltage between the anode and the cathode of the tube is limited to desired conditions as to amount and phase.

With separately excited senders, the control sender may be constructedas shown'in Fig. 2 but also in any of the usual connections. I

For certain cases it may be desirable to em ploy a control sender having tubes of very small power and to amplify the power in several stages until the final power to be transmitted has been attained.

It is known in this artthat the tubes of the control senders are able to transmit a multiple, the five to ten-fold, of the power which is to be transmitted to the grid of a following tube, the following tubes in senders being usually ar- 40 ranged not in the negative but in the positive range in order to obtain outgoing power of sufficient intensity. The tubes are utilized more eliiciently in the positive range which is important in senders though unimportant in receivers.

The power which the control sender, or each of its tubes, transmits to a following tube, is small as compared to what it might transmit and, for the same reason, the effective resistance transmitted to the anode circuit is comparatively small. This justifies the employment of the described connection for senders.

An example for a sender of this type is illustrated in Fig. 3, I5 being the tube 'ofthe control sender which is constructed as described with reference to Fig. 2, with grid circuit 2, backcoupling coil l4, battery 4, condenser 5', and ohmic resistance 6'. I6 is an intermediate tube amplifier designed as described with reference to Fig. 1, and I1 is the final tube. Obviously, more than one valve I6 might be provided.

In connection with the final valve 11, a choke coil 22 may be provided instead of the ohmic resistance 6 in the direct current circuit by which arrangement losses in the alternating current circuit of the tube 11 are eliminated. On the other hand, the tuning of the series unit I, 8 is not altogether definite in this case.

Besides the series unit, additional alternating current circuits [8, l9, and 20, 2| are provided which are preferably tuned to the first and second overtones, respectively, of the effective waves to be radiated. In this manner the usual intermediate circuits for eliminating the overtones which require large and expensive condensers etc., and cause loss, are dispensed with and this is favourable as compared with the usual system. But, if desired, any system of the usual type may be provided for the final tube ll.

Another good feature of the connection illustrated for the final tube I1 is that the alternating anode voltages which may form correspond only to the ohmic resistance of the series unit plus the effective resistance which the antenna transmits to the unit. Formation of voltage by prevailing self-inductance or'capac'ity in the anode circuit cannot occur.

Care should be taken when designing the alternating current circuits 1, 8, l8, l9 and 20, 2| lest degrees of freedom might form which cause undesirable vibrations.

. For certain purposes it may be desirable toopcrate a separately excited sender not by a control sender, as shown, but by a frequency obtained through receptiomor with the multiple of a received wave. The power input available is generally very small as compared with the power it is desired to emit and it will be necessary in such a case to amplify the small power in several stages before it is emitted. For this object, the improved connection described is particularly suitable as with the usual connections selfoscillation of the tubes may occur.

One of the purposes referred to above is the operation of several broadcast senders with the same wave. It is desirable to operate in this manner if the senders emit the same programme. The wave length must be absolutely uniform for all senders as otherwise superposed tones might occur. The problem is solved by transmitting a control wave to the several senders through space or through cables. Preferably the frequency of the control wave is amplified at the senders and the senders are operated at this amplified frequency. The connection of the several tubes as described is suitable for this purpose. The several senders may be operated at the same frequency or at various frequencies in groups.

Obviously, any means for telephone operation may be connected with the systems described.

Another case is the amplification of low frequencies by a highly frequent control wave, as, for instance, capacitative microphone systems of known type in which a separately generated highfrequency wave is acted on. In order to obtain speaking currents of lowfrequency, as required for senders, the low-frequency current is separated from the high-frequency wave, and amplified further at high frequency. With the systems described the low-frequencyamplification maybe replaced by further high-frequency amplification and by rectifying at the end of the amplification, that is, without further low-frequency amplification, or to operate directly a telephone sender without rectifying. This means that a telephone sender of very small power is directly influenced by a capacitative microphone, and the modulated small high-frequency is amplified in a suitable number of stages of highfrequency tubes until the power required has been attained.

Such a telephone transmitter has been illustrated in Figure 4 wherein an oscillation generator and coupling circuit, as shown in Figure 3, are used. Voice currents may be impressed on the microphone 25, shunted by resistance 26, to modulate at signal frequency the impedance of the grid to cathode circuit of the back coupled oscillator to modulate at signal frequency the oscillations produced. The circuit to the left of the tube I6 in Figure 4 mar be the same as the circuit in Figure 3.

It will be understood from the foregoing that my improved connection is equally applicable to 5 senders and receivers and enables me to build receivers operating principally at high frequencies, the high-frequency amplification being practicable to an extent not attained in the existing systems. High frequency is so desirable m for receivers because it intensifies low-frequency interferences which often are troublesome, to a lesser degree than with low-frequency amplification. High-frequency amplification may be extended until it is possible to use telephones 15 the operation of which is based on capacitative action. This eliminates for instance receiver distortions which are brought about by the nonstraight-line operation of the usual rectifiers, such as detectors and audions. 20

It should be noted that in the tubes used in connection with my system the steepness of the characteristic or mutual conductance is important for the degree of amplification. This is in contradistinction to the usual amplifier systems where the degree of amplification with adapted suitable outerresistance is only determined .by the inverse or reciprocal amplification factor of the given tube. The feature that in the present case the degree of amplification is :a 30 function of the steepness of the characteristic or mutual conductance, is a particular advantage in that it is possible to obtain higher amplifications by increasing the steepness. As in the present instance the alternating voltages between the 35 anodes and the cathodes of the valves are but small it is possible to use tubes characterized by a high inverse-amplification factor which may be operated on the other hand at correspondingly low anode voltage.

I claim:

1. A connection for the operation of high-frequency generators and amplification systems comprising a tube generator of the thermionic type having control grid and cathode connected in a frequency determining circuit including an inductance, a, series unit including a capacity, a self-inductance and a coupling inductance arranged intermediate the anode and the cathode of said tube generator, and tuned to the operat-fiO ing frequency of the generator, .said coupling inductance being coupled to-said first named inductance to produce sustained oscillations'in said tube and circuit, a direct current circuit connected between said anode and cathode, and a ,coupling for transmitting the voltage across oneof the inductancesin said series unit to the control grid of another tube.

2. A connection for the application of energy from a high-frequency generator to an amplifier system without producing appreciable potential changes across the output of the generator comprising a thermionic tube generator, a series unit including a capacity coupling coil and a selfinductance arranged intermediate the anode and the cathode of said generator and tuned to the operating frequency of the system, a source of electric energy connected in parallel to the impedance between the cathode and the anode of said first-mentioned tube generator and to said unit, an ohmic resistance connected in series with said source of energy, and a connection between the terminals of said self-inductance and the input electrodes of said amplifier system.

3. Signalling means comprising an oscillation 76 source including, a thermionic oscillator tube having an input circuit connected to its input electrodes, said tube having output electrodes and an alternating current output circuit connected to said output electrodes and coupled to said input circuit, a thermionic relay tube having control grid and cathode electrodes, and a device for transferring voltage'changes from the output circuit of said thermionic oscillator tube to the control grid cathode electrodes of said thermionic relay tube comprising, a direct current circuit including an ohmic resistance connected between the output electrodes of said thermionic oscillator tube, an alternating current circuit including series reactances tuned to resonance at the frequency at which said oscillator tube operates and connected in said alternating current output circuit in parallel with said direct current cir-' cuit, and a circuit for connecting the control grid and cathode of said relay tube in parallel with one of said series reactances.

4. Signalling means comprising an oscillation source including, a thermionic tube having an input circuit connected to its input electrodes, output electrodes, and an alternating current output circuit connected to said output electrodes and coupled to said input circuit, a thermionic relay tube having control grid and cathode electrodes, and a coupling circuit for'transferring voltage changes from the output circuit of said oscillation source to the control grid cathode electrodes of said relay comprising a direct current circuit including an ohmic resistance and a source of potential connected between the output electrodes of saidfirst named thermionic tube, an alternating current'circuit including an inductance and variable capacity in series'connected in parallel with said direct current circuit, said capacity and inductance tuning said alternating current circuit to series resonance at the frequency of the oscillations developed in said first named tube and circuits and a circuit including a source of potential for connecting the control grid and cathode of said relay tube in parallel with said inductance. i

5. Signalling means comprising, an oscillation generator including a thermionic tube having an input circuit and a compound output circuit including a direct current branch and an alternating current branch coupled to said input-circuit to produce sustained oscillations, a thermionic relay having input electrodes, and means for transferring voltage oscillations from the output electrodes of said oscillation generator to the input electrodes of said relay comprising, an ohmic resistance in the direct current branch of said compound circuit, inductive and capacitive series, reactances in' the alternatingcurrent branch of said compound circuit in parallel with said ohmic resistance, said reactances being tuned to series resonance at the frequency of the oscillations produced by said generator, and means for connecting one of said'reactances with the input electrodes of said thermionic relay,

6. Signalling means comprising, an oscillation generator including a thermionic tube havinga tuned input circuit and a compound output cir- 10 cuit, a portion of which is coupled to said input circuit to produce sustained oscillations, a ther mionic relay having inputelectrodes, and means for transferring voltage oscillations from the output of said oscillation generator to' the input 5;

electrodes of said relay comprising, an ohmic resistance and a source of potential in a portion of said compound circuit, an inductance and capacity in series inanother portion of said compound circuit in parallel with said ohmic re- 20,

sistance, said inductance and capacity tuning said portion of said compound circuit to series resonance at the frequency of the oscillations produced by said first named tube and circuits,

and means for connecting one of said reactances 5 with the input electrodes of said relay.

' actances connected in parallel with said ohmic resistance and source of potential, said reactances being resonant at the frequency of the potential variations developed by said generator, and a circuit for connecting the input electrodes of said relay in shunt with a portion of said reactances.

8. Signalling means as recited in claim 5 in 5 which the input electrodes of said thermionic relay comprises a control grid and a cathode, and in which said thermionic relay has an anode electrode connected to a load circuit to supply the amplified voltage oscillations thereto, said load 50 circuit including a plurality of circuits, each comprising capacity and inductancein series across the anode and cathode of said thermionic relay, each of said series circuits being series resonant at a. different frequency other than the'funda- 55 mental frequency produced by said generator.

WALTER scHZiFFER.

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