US2206388A - Oscillation generator - Google Patents

Description

U Y 2, 1940- w. BUSCHBECK OSCILLATION GENERATOR Filed Aug: so, 1938 WERNER BUSY/ZZ- C /E BY A TTORN E Y.

Patented July 2, 1940 UNITED STATES PATENT OFFICE OSCILLATION GENERATOR tion of Germany Application August 30, 1938, Serial No. 227,482 In Germany August 20, 1937 6 Claims.

The present invention is concerned with a tube circuit organization adapted to amplify or generate alternating potentials, especially of high frequency, the output of which contains only the frequency to be amplified, and is free from harmonics or overtones. It is basically well known in the prior art that the harmonic content of oscillations can be diminished by coupling the load to a capacitor included in the inductive branch of the oscillatory circuit of the tube.

If this means proves insufiicient recourse may also be had to several series-connected tuned circuits whereby the harmonic content in terms of percentage may be diminished practically to any desired level. However, such circuit organizations involve the drawback that complex re-tuning is required in the different elements in case there is a change in wavelength. As a matter of fact, such re-setting is practically impossible in a self-oscillatory transmitter because of the oscillation hysteresis (or pull). phenomena inhering in the multi-wave nature of the arrangement.

Now, the problem and aim of the invention is to suppress as far as possible all harmonics in an amplifier or oscillation generator, and to provide means for readily adjusting the apparatus to different wave lengths as desired. The invention resides in the subdivision. of the capacity of an oscillatory circuit, in coupling the output of the tube with one of the resultant partial capacities and the load device with the respective other portion of the capacity, while a condenser is connected between the junction of the said capacities and the corresponding pointof symmetry of the inductance of the oscillation circuit.

The invention will now be described in more detail, reference being made to the accompanying drawing in which Figure 1 shows a circuit diagram of an oscillation. generator which is adapted to the requirements for practicing the invention, and

Fig. 2 shows a modified circuit arrangement.

Referring first to Fig. 1, it will be observed that the Oscillation generator may be either of the self-oscillatory or the master-excited type. The tube R has an output circuit which includes the capacitor C1 of the oscillation circuit, while the load V is connected across another capacitor C: which is in series with the capacitor C2 merely for the purpose of securing a voltage divison favorable to the load. The three capacitors C1, C2 and C3 are effectively connected in series and are in parallel with the inductance of the resonant circuit. A source of direct current potential is supplied through the choke coil 4 to the anode of the tube R, is being understood that if, as shown, the cathode 3 is grounded, then the negative terminal of said direct current source will also be grounded.

The control grid 5 is connected through a gridleak resistor 6 and a biasing source I to the cathode 3.

The inductance of the resonant circuit comprises two portions L1 and L2, and these may be tuned jointly. The cathode 3 is directly connected to the junction point K of the resonant circuit. Between this junction point K and the junction point M for the inductances L1 and L2 is connected a capacitor C4. For the sake of simplicity it may be assumed that the capacitance C1 is equal to the series-capacitance C2+C3 also that L1=L2. If, then, a current is flowing through the oscillation circuit it will be evident that points as regards the fundamental frequency of the system K and M are equi-potential points and that the condenser C4 will play no part at all as long as its reactance is less than the load resistance V coupled in the lower part of the circuit between points K and M. This latter condition is due to the fact that in the lower part of the circuit, as a result of series resonance of C3, C2, and L2, there remains merely the transferred active resistance of the load between K- and M, with capacity C4 being in parallel relation thereto. The tuning of the entire circuit'is merely a function of the quantities C1 and L1 (which, by assumption, are equal to the corresponding elements of the lower part of the circuit) so that the tuning is effected simply in accordance with the formula which is tantamount to putting XL1XC1=0, where XL and X0 are the reactances of the coil and of the capacity.

However, this tuning arrangement is not the only feasible one, as can be seen from the modified circuit diagram shown in Fig. 2. A state of tuning exists when the circuit between the points A and K represents an ohmic resistance. Presupposing low circuit damping, this will be true as may be confirmed by an easy calculation if XL]=XC'], as already shown above. However, there exists a second solution, namely, when XL =Xc --l2.Xc

and this implies or corresponds to in-phase excitation of the two parts of the oscillatory circuit, the two points A and B being at the same potential, while points K and M, on the contrary, have potentials that are displaced an angle of 180 degrees to each other. This last-mentioned provision for tuning will be readily understood by imagining the two points A and B to be inter-connected, though it is to be admitted that this assumption will be valid only for the fundamental wave.

The testing of a circuit organization as here disclosed showed that there are two possibilities for the production of oscillations, both of which are equivalent and result in fundamental-wave tuning of the circuit. In both instances the harmonic components of the output current from the discharge :tube are to a large extent shortcircuited by the capacitor C1 and the remainder of such components is substantially dissipated after flowing through the coil L1 by virtue of a low impedance capacitor C4. Due to the large capacitance of the element C4, no appreciable harmonic wave potential will arise across the same. Such remainder of harmonics as may still exist and traverse the coil L2 reaches the cathode by way of the capacitors C2 and C3. the latter be-- ing so large again that no appreciable potentials will be built up in them.

In other words, capacitor C4 to a surprisingly great extent acts as a means capable of suppressing harmonics, regardless of whether the circuit oscillates in phase opposition (180 degrees phase difference) or whether it oscillates in an in-phase state of tuning. The circumstance that points K and M operate in phase opposition in the presence of in phase' excitation may be utilized in a very simple manner for self-oscillation of the circuit organization in such a way that point M, as indicated in Fig. 1 by broken lines, is united with the grid of the tube either directly or else through a condenser. The tube thus delivers to the load merely a single oscillation corresponding to in-phase tuning and practically free from harmonics. A quantitative investigation of the conditions then prevailing results in the following numerical values which have been calculated by assuming a feed-back factor of k= The left-hand column of the tabulation contains the ordinal number of the harmonics '(n), while the other column contains the ratio between the amplitude I1 for a given harmonic, with omission of the condenser 04, and the amplitude I2 when the said condenser is included in the circuit scheme:

It will be noted therefrom that, for instance, the fourth harmonic is cut down by the factor 110 in a scheme as here disclosed as contrasted with circuit organizations disclosed in the prior art, and this means practically complete suppression.

The property of point M, namely, to operate in phase opposition to the plate or anode in the presence of in-phase tuning may be utilized for the purpose of deriving a neutralizing voltage rather than for self-oscillation of the tube. In this instance, the said point M must be un ted with the grid of the tube by way of a suitable capacity.

So far as the suppression of the harmonics is concerned it is immaterial, as already pointed out, whether the tuning chosen for the circuit is in phase or in phase opposition, for in either case, in case of wave change, tuning may be obtained simply by a variation in the inductance L1, L2, the drive means of which should preferably be inter-locked mechanically. From a construction view point excitation in phase opposition of the oscillation circuit ofiers advantages in case of master excitation of tube R for the reason that there is no potential of fundamental wave between the points K and M so that the condenser C4 may be made correspondingly small, and this is a very valuable fact looked at from the angle of reduction of inner or inherent condenser inductance, for such stray inductance may play a very disturbing part where extremely high harmonics are dealt with. In the case of selfoscillation of the circuit arrangement, however, in-phase tuning is preferable, alone for the reason that the taking off of the feed-back potential at point M becomes extremely simple. Moreover, also the harmonic potentials arising at the grid of the tube are led oil through condenser C4 to the cathode with the result that the other properties of the circuit scheme which tend to diminish the harmonics will thus be boosted.

The invention, when self-oscillatory, is particularly adapted to measuring and transmitter control work where the demands regarding freedom from harmonics are very severe, while in master-excited circuit schemes the invention will be found advantageous for power stages working upon an open antenna.

I claim: 1. In a filter system for the output of an elec tron discharge tube, a parallel resonant circuit including a capacitor connected between theanode and cathode of said tube, a second parallel resonant circuit including a plurality of serially connected capacitors, the two resonant circuits having equivalent and interconnected inductances, common tuning means for the two said resonant circuits, a load connected in shunt with one only of said serially connected capacitors, and means connected between certain points in the capacitive and inductive branches of said resonant circuit, said points being of substantially equal potential when co-phasally excited at the fundamental frequency of said oscillation generae tor, for by-passing currents of higher frequen- CIBS. 2. A filter system fed with energy from a electron discharge tube, said system comprising a parallel resonant output circuit for said tube, another parallel resonant circuit having a capacitor in common with said output circuit, equivalent interconnected inductances each forming a part of one of said resonant circuits respectively, common tuning means for the two said resonant circuits, a plurality of serially connected capacitors in the second said resonant circuit, and a load connected across one only of said capacitors, the first said capacitor constituting means for dissipating energy of higher frequencies than the frequency to which said resonant circuits are tuned. 3. A coupling circuit arrangement comprising two interconnected parallel resonant circuits, a plurality of serially connected capacitors in one of said resonant circuits, a load in shunt with one of said capacitors, common tuning means for the two said resonant circuits, and means, in-

cluding a low impedance path for currents of harmonic frequencies with respect to the frequency to which said resonant circuits are tuned, said means being connected across selected points in the inductive and capacitive branches of said resonant circuits and serving to dissipate said currents of harmonic frequencies.

4. In combination, a resonant circuit including an inductance and a capacitor, a second resonant circuit comprising an inductance and a plurality of serially connected capacitors, means common to both said circuits for adjusting the L/C ratio thereof in like manner and to resonate with a fundamental frequency of output from a given discharge tube, a load connected in shunt with one of the capacitors in the second said resonant circuit, and means intercoupling two selected points in said resonant circuits for dissipating harmonic frequency components of the output energy from said tube, one of said points being disposed on the capacitive side of said resonant circuits, and the other of said points being disposed on the inductive side of said resonant circuits.

5. The combination according to claim 4 and having means for exciting said selected points in phase opposition.

6. The combination according to claim 5 and having means for exciting said selected points co-phasally. I

WERNER BUSCI-IBECK.

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