US2409620A - Oscillation generator - Google Patents

Description

Patented I@cla 22, 1946 OSCILLATION GENERATOR Walter W. Fritschi, Manhasset, N. Y., assignor to Bell Telephone Laboratories, Incorporated,` New York, N. Y., a corporation of New York Application January 17, 1942, Serial No. 427,131

7 Claims. (Cl. Z50-36) This invention relates tol oscillators and particularly to vacuum tube oscillation generators of the feedback type.

The invention has for its object the provision of a simple, single vacuum tube oscillator adapted to supply signaling current of a desired frequency interrupted at a desired rate, and the production of sufficient output power `'in 'such an oscillator with the amplitude ratios desired and with satisfactory limits of voltage and frequency variation under variable load conditions.

This invention is an oscillator comprising a single vacuum tube arranged to produce oscillations of a desired signaling frequency and to interrupt the signaling frequency at a desired rate. A feature of the invention is a single vacuum tube oscillator designed to simultaneously produce oscillations at the signaling frequency andat the rate of interruption desired, the ratio between the amplitudes of the twoy frequencies being adjusted so that the feedback of the lower tive impedance-voltage coefficient, across the network which is tuned to the signaling frequency to obtain a more constant amplitudeoi the signaling frequency.

A clear and complete understanding of the invention will be facilitatedby a.' description of to generate oscillations of a desired interrupting frequency at which the oscillations of the signalingfrequency are interrupted;' p A Fig. 2 shows an oscillogram V'of the output of the oscillator shown in Fig. 1; thi's'envelope shape 2 is obtained when the oscillator is designed to satisfactorily regulate the amplitude ofthe voltage of the signaling frequency; and

Fig. 3 shows the envelope shape when insuiii-` cient voltage regulation is provided.

The oscillator shown in Fig. 1 of the drawing comprises a vacuum tube Ill, a feedback resistor I9, a variable condenser 2l), an induction coil comprising windings 2l and 22, a potentiometer comprising resistor 23 and brush 24, an induction coil comprising windings 3|, 32 and 33, impedance element 35, condensers 35 and 3l', a potentiometer comprising resistor 38 and brush 39 an output transformer Ml, and output terminals 4I and 42. The tube I0 is of the screen grid high amplification type having a thermionic cathode I5, control grid Id, screen grid I3, anode II, and a pair of electron beam conning plates I2, positioned between the anode I I and screen grid I3. Reference may be had to the patent to Ol. H. Shade No. 2,107,520, granted February 8,`1938for a detailed description of atube lof the preferred structure and character. The cathode I5 is indirectly heated by a heating element I6 in usual manner, and the beam deflecting plates l2 are electrically connected to thecathode. While the tubeshown is of the beam type, a high amplification tube without beam deiiecting plates maybe used. The anodefcathode space current circuit is traced from anode I! through winding 2l of oneinduction coil, through winding 3| and a partof winding 32 of the other `induction coil, brush 30, and through battery 50 to the cathode I5. The condenser 36 is bridged across the windings 3l, 32

and `33 to form a tuned network which is resonantL to the desired signaling frequency, fory instance l000"cycle's'per`second; and the variable conf` denser 2Dis bridged across the winding 2I to form altuned network which is resonant at the frequency at which. it Yis desired that the signaling frequencybe interrupted, for instance 15 cyclesV with winding 22thence to potentiometer'brush Y.

39, through resistor`38 to cathode I5. The control grid" is not biased bya direct current` source and bothfthe signaling frequency andthe interrupting frequency are fed back tol the controlgrid; thel. `amount of feedback being dependent `upon the adjustment oflbrushes 2li and `3i). The resistor I9- has a high resistance to'limit the grid circuit.

The primary winding of output transformer 40 is bridged across the winding 3l and an impedance element 35 having a negative temperature-voltage coefficient, is bridged across the winding 33 and a part of the winding 32 as determined by the position of brush 34 to limit the amplitude of the oscillations of the signaling frequency. The element 35-may consist of silicon carbide of such dimension and character as to provide the desired range of impedance. By adjustment of brush 35 the portion of induction coil winding 32 which is included in the anode-cathode circuit may be varied and by adjustment of brush 34 the amount of inductance which is shunted by element 35 may be varied. The condenser 3l, which is in series with potentiometer resistor 38, is effective to prevent direct current through the resistor.

Assume that the feedback potentiometers have been adjusted to obtain the desired feedback potentials and that the oscillator is placed in operation, for instance, by the closing of the battery connections. Immediately, both of the tuned 'circuits begin to build up oscillations at a very high rate, the initial impedance of element 35 being high. As the impedance of element 35 decreases, the feedback decreases until a point of stability is reached. `rIhereafter the element 35 tends to` compensate for any changes which affect the amplitude of oscillation, for instance, changes in load, battery Voltage and, within limits, the amplification provided by the tube. A similar impedance element may be connected across winding 2i to compensate for such changes in amplitude of the oscillations at the interruptingfrequency. Although it is believed to be preferable to operate the oscillator with zero grid biasas shown in the drawing, satisfactory operation is obtained by providing a negative grid bias, inlconventional manner. With zero grid bias,'the signaling frequency is interrupted during the positive half cycle of the interrupting frequency; and with a negative grid bias, the signalingyfrequency is interrupted during the negative half-cycle of the interrupting frequency. When the grid bias is zero, there is current in the grid-cathode circuit during the positive halfcycle of the interrupting frequency; and, with a low enough ratio between the amplitudes of the signaling and interrupting frequencies, the drop inpotential in resistor I9 is effective to substantially prevent variation in the grid potential due to the signaling frequency so that oscillation at the signaling frequency ceases. With zero grid bias, there is no grid current and no drop; in potential in -resistor I9, during the negative halfcycle of the interrupting frequency and the amplication of the tube is sufcient to maintain oscillation at the signaling frequency. If a source of negative grid bias is provided in the control grid-cathodecircuit, the instantaneous potential of the grid varies under control of the feedback potentials; and in this case, there is no grid current and no drop in potential in resistor I 9 except during excessive peaks in the sum of the instantaneous' feedback potentials of both frequencies. With sufficient regulation provided by element 35, such excessive peaks will not occur or will not 'be` suiciently long in duration to suppress oscillation at the signaling frequency during' positive half-cycles of the interrupting frequency; but, during the negative half-cycles, the grid potential is driven to and beyond the oscillation cut-off point by the energy stored in the circuit which is resonantv at the interrupting frequency. Whenlthis storedl energy is dissipated and the grid potential again builds up to and beyond the cut-off point, the signaling frequency reappears. Thus in either case, that is with zero grid bias or with a negative grid bias, the signaling frequency voltage is stopped and started at the interrupting frequency and substantially complete suppression of the signaling frequency is obtained during one half-cycle of the voltage of the interrupting frequency.

The oscillograms shown in Figs. 2 and 3 indicate that the envelope shape of the signaling frequency may be regulated by the character of the negative-impedance element 35, a satisfactory envelope being illustrated in Fig. 2 and an unsatisfactory envelope resulting from insufficient regulation on the part of element 35 being illustrated in Fig. 3. These two oscillograms illustrate the range of envelope shapes which it is possible to obtain through control of the amplitudes of the two frequencies of oscillation by the element 35 and the amount of attenuation in the feedback paths. There is, of course, a limit to this regulating action and the envelope shape shown in Fig. 3 illustrates a case where there is insufcient regulation and the signaling voltage is entirely eliminated when the grid potential decreases to or beyond the cut-off value.

The useful output voltage may be obtained by directly connecting the load to the terminals lll and 42; or if greater output or better regulation is required, an intermediate amplifier may be provided. The effective length of each period of signaling frequency oscillation is slightly less than the length of the positive half cycle of the interrupting frequency due to a change in frequency during the build-up and decay of the signaling voltage. The effective duration of the signaling voltage is illustrated in Fig. 2.

The advantages of the above-described oscillator over known methods of generating a signaling voltage of desired frequency and periodically interrupting this voltage at a desired rate reside in its simplicity, its low initial cost, and the low cost of maintenance Which results in part from the lack of moving parts.

What is claimed is:

1. A signaling current generator comprising a single thermionic tube, two tuned circuits in the anode-cathode circuit of said tube, one of said tuned circuits resonant at a desired signaling frequency, the other of said tuned circuits resonant at a desired lower frequency, feedback connections frorn said tuned circuits to the control grid of said tube, and means controlling the relative amplitude of the feedback from said tuned circuits to effect a periodic interruption of the oscillations of said signaling frequency at said lower frequency.

2. In an oscillation generator, a single Vacuum tube, a network tuned to resonance at a desired signaling frequency, a network tuned to resonance at a desired lower frequency, said networks connected in the anode-cathode circuit of said tube, feedback connections from said netv works to the control grid of said tube, means controlling the relative amplitude of the feedback from said networks to effect a periodic interruption of the oscillations of said signaling frequency at said lower frequency, output terlminals, and means connecting'said terminals to thenetwork tuned to the signaling frequency.

3." In an oscillation generator comprising a single vacuum tube, two tuned networks connectedin the anode-cathode circuit of said tube,

each-of said networks .comprisingan inductive winding and a condenser, one of said networks being resonant at a desired signaling frequency,

the other of said networks being resonant at a desired interrupting frequency, feedback connections from said networks to the control grid of said tube, means controlling the relative amplitude of the feedback from each of said networks to effect a periodic interruption of the oscillations in said one network at said interrupting frequency, and an impedance element having a negative impedance voltage coefficient shunting a part of the inductive winding of the network which is tuned to said signaling frequency, thereby to regulate the amplitude of the oscillations of the signaling frequency.

4. In an oscillation generator comprising a single vacuum tube, two tuned networks connected in the anode-cathode circuit of said tube, each of said networks comprising an inductive winding and a condenser, one of said networks being resonant at a desired signaling frequency and the other of said networks being resonant at a desired interrupting frequency, an adjustable feedback connection from said one network to the control grid of said tube, an adjustable feedback connection from said other network to the control grid of said tube, output terminals connected to the inductive winding of said one network, and an impedance element having a negative impedance-voltage coeicient connected to the inductive winding of said one network to constitute a voltage regulating load. Y

5. In an oscillation generator comprising a single vacuum tube, two tuned networks connected in the anode-cathode circuit of said tube, each of said networks comprising an inductive winding and a condenser, one-of said networks being resonant at a desired signaling frequency, the other of said networks being resonant at a desired interrupting frequency, feedback connections frorn said networks to the grid of said tube, a high resistance connected in the grid-cathode circuit, means controlling the amplitude of the feedback from each of said networks to eifect the periodic interruption of the oscillations of said signaling frequency at said interrupting frequency, output terminals connected to said one network, and an impedance element having a negative impedance-voltage coefficient connected across a part of the inductive winding of said one network.

6. In an oscillation generator comprising a single vacuum tube, two tuned networks connected in the anode-cathode circuit of said tube, each of said networks comprising an inductive winding and a condenser, one of said networks .being resonant at a desired signaling frequency, the condenser of said other network being variable so that the frequency at which said other network is resonant may be adjusted within desired limits, feedback connections from said networks to the grid of said tube, means controlling the amplitude of the feedback from each of said networks to effect the periodic interruption of the oscillations of signaling frequency at the frequency to which said other network is resonant, output terminals connected to said one network, and an impedance element having a negative impedance-voltage coefficient connected to the inductive winding of said one network to regulate the voltage impressed across said terminals.

7. In an oscillation generator comprising a single vacuum tube, two tuned networks connected in the anode-cathode circuit of said tube, a rst one of said networks comprising one winding of an induction coil and a condenser, said first network being resonant at a desired low frequency, the second one of said networks coinprising windings of an induction coil and a condenser, said second network being resonant at a desired signaling frequency, means comprising another winding of the first-mentioned induction coil `and a potentiometer connected across said other winding for impressing an alternating potential of said low frequency on the control grid of said tube, means comprising a potentiometer and a condenser connecting said potentiometer in series with said second network for impressing an alternating potential of said signaling frequency on said control grid, output terminals connected to said second network, and means including an impedance element having a negative impedance voltage coefficient connected across one of the inductive windings of said second network for regulating the amplitude of the oscillations of said signaling frequency, whereby said oscillations are interrupted periodically at said low` frequency and the voltage impressed across said terminalsv is maintained at a desired amplitude.

WALTER W. FRITSCHI.

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