US2565842A - Frequency stabilizing device for high-frequency oscillators - Google Patents

Description

Aug. 28, 1951 M. DENIS 2,565,842

FREQUENCY STABILIZING DEVICE FOR HIGH-FREQUENCY OSCILLATORS Filed 001;. 22, 1947 f rrezdor 8 Mica. Dew/sp M10} Y @genf:

Patented Aug. 28, 1951 FREQUENCY STABILIZING DEVICE FOR HIGH-FEEQUENCY OSOILLATORS Marcel Denis, Paris, France, assignor to Compagnie Generalc Be '1. S. F.

France a corporation of Application October 22, 1947, Serial No. 781,352 In France October 3, 1946 Section 1, Public Law 690, August 8, 1946 Patent expires October 3, 1966 Claims. 1

It is known that the frequency of the oscillations furnished by certain generators of short or ultra-short waves is influenced by the value of the supply potentials of one or more electrodes. For example, the variation, over a certain range, of the continuous potential applied to the reflector of a reflex Klystron causes a variation in frequency of the potential delivered on the output side of the apparatus.

This feature can be utilised for purposes of frequency stabilisation by proceeding in the following manner: From the output of the generator a small fraction of the power is taken off and injected into an auxiliary device which reacts on the said generator, applying thereto, with the aid of a suitably selected electrode, a regulating potential. If, for example, the frequency tends to increase, this regulating potential will vary in such sense as to cause a reduction in the said frequency, and vice versa.

The present invention has for its object to contrive a device which, basing itself on this principle of operation, shall enable eflicient stabilisation to be obtained.

The process consists essentially in the use of a resonant space or cavity the resonance frequency of which is made periodically variable on each side of a mean value in by means of an auxiliary generator; this cavity is, on the other hand, excited by the fraction of power taken off from the generator output; at the output of the resonant cavity there is delivered an amplitudemodulated signal, the intensity of which depends upon the difference between the generator frequency and the resonance frequency To; the said signal, after detection and amplification, is fed back to the selected electrode, there to act as a regulator. The system thus operates after the fashion of the well-known counter reaction circuit, all variations of frequency which tend to arise being immediately reduced and divided by a coefficient of regulation K, greater than unity.

Furthermore, circuits arranged according to the present invention enable the following results to be obtained.

l. The regulator signal is zero when the outward frequency of the generator has precisely its normal value.

2. Regulation is equally efficient in both directions, tendencies to reduction of frequency being corrected as well as tendencies to increase of frequency.

3. The above-defined coefficient K varies little as a function of the separation between the actual value of the frequency and. its normal value.

4. The coefficient K. remains practically constant, although the power furnished by the generator may vary within wide limits.

The invention will be more clearly understood with the assistance of the following description, which is intended to be read in conjunctionwith the accompanying drawings. An embodiment of the invention and some modifications thereof are illustrated purely by way of example.

Figure 1 shows, diagrammatically, one circuit arrangement in accordance with the invention.

G indicates the generator, for example, a reflex Klystron, the frequency of which has to be stabilised by acting on the potential applied to the reflector electrode GR.

V is a resonant cavity, constituted for example, by a box made of silvered Invar metal, so as to be but little sensitive to variations of temperature.

A loop B takes a small fraction of the power delivered by the Klystron; this loop is formed by a conductor doubled back on itself and having one of its extremities soldered to the wall of the apparatus; the extension of this conductor constitutes, with the addition of a suitable envelope, a coaxial cable D1 affording connection with the cavity V, wherein the other end of the said conductor is terminated by another loop B. Thus the high frequency power picked up by B in G is applied to the excitation of the resonant cavity V.

On the other hand, a modulator m is fed with a low frequency current from a source S, through the intermediary of the secondary winding of the transformer T1. This modulator is connected to V by means of a coaxial cable D2 also terminated by two loops in and D2. The modulation produced by modulator m has the effect of periodically causing the reactive part of theinrpedance of V to vary, thus varying the resonance frequency. It is not essential that modulation of the resonance frequency of cavity V be effected electrically; it may, instead, be effected by mechanical means, that is to say, by mechananical variation of a geometrical dimension of V.

An output loop I) located at the extremity of a coaxial cable D, feeds a crystal detector K, interposed in the central conductor of the cable; thus, at the output end of the said cable, there appears a periodic and non-sinusoidal signal at the frequency of the source S, the amplitude of this signal depending upon the frequency variation 3 of G. Condensers C short-circuit the output in such manner as to eliminate very high frequencies. On the other hand, a loop b, excited in the interior of the Klystron, feeds into another coaxial cable D, provided with an internal crystal detector K and with condensers C for elimination of the high frequencies. At the output end of this cable assembly there appears a continuous polarization current In which reacts on the output of the crystal K and makes the regulation practically independent of the power furnished by the generator. An inductance L1, with which there may be associated a tuning condenser Ci, prevents the signals at the frequency of the source S from being diverted toward K.

The condenser C blocks the continuous currents deriving from one or the other of the detector K or K, while allowing the useful signal to pass into the resistance R.

The potential developed across the terminals of resistance R, of the same frequency as the source S, must first be filtered, in a suitable network followed by a selective amplifier, in such manner as to extract a sinusoidal signal at the frequency of the source S. The filter and amplifier assembly is represented diagrammatically at AF. The signal is then fed to a detector, which latter must be designed in such manner that detected continuous potential changes in direction at the same time as the variation of frequency tending to be produced in the generator G. To this end, various combinations may be used, a first example being seen in the circuit arrangement of the pentode P. The output potential of the assembly AF is applied to the control grid; the cathod in accordance with current practice, is biassed positively by the mean anode current passing through the resistance R1; the second grid is excited by the output from the secondary winding 2 of the transformer T1, passing through a resistance R2; the third grid is connected to the cathode and, finally, the plate is supplied with a continuous potential Us, fed through an anode resistance r. The capacity C2 has for its purpose to eliminate the alternating potentials from the output of the pentode, so that the output delivered to the conductor A is a continuous potential, the variation of which depends, in magnitude and in sign, upon the variations'of frequency of the potential induced in the loop B. Finally the conductor A is connected to the electrode GR, the potential of which reacts on the frequency of the generator G.

The role of th resonant cavity V is illustrated by Figure 2, in which C is the resonance curve of this cavity, that is to say, the variation of the potential U available at the output for a given high frequency excitation, plotted as a function of the frequency f of the generator. Thepeak of the curve corresponds to the normal frequency In.

If the frequency f of the generator tends to diminish, the modulation of the source S of Figure 1 will cause the point of operation to oscillate between M and N, for example, the segment MN being located to the left of It. If, on the contrary, f tends to increase, the point of operation will oscillate between M and N, the segment MN' being located to the right of In. Now it will be seen that, owing to the shape of the curve C, the ordinate Mm is smaller than the ordinate Nn; on the contrary, Mm is larger than Nn'. It follows that displacement of the point of operation from M to N will produce an increase of the potential at the output of the cavity V; displacement from M to N will, on the contrary, produce a reduc- P, coming directly from the source S through the resistance R2, is of the same frequency as the potential coming from AF and applied to the first grid. It will always be possible to harmonise the passages through zero of these two potentials, applied, respectively, to these first two grids; for this purpose there may, if necessary, be interposed in the circuit a suitable dephasing network (not shown). Such a network might, for example be interposed between the transformer secondary winding 2 and the resistance R2.

From the arrangement described the following result is obtained; for a certain sense of variation in the frequency of generator G, the potentials respectively impressed on the two first grids of the pentode P will be exactly in phase; if this variation takes place in the reverse sense, these two said potentials will be exactly in opposition. It will be understood that the current detected in the anode circuit will increase in the case of the first hypothesis and will diminish in the second case; this obviously signifies that the continuous potential finally applied to the electrode GR will undergo a variation the sign of which will depend upon the variation of frequency tending to arise in the generator G. This frequency can, therefore, be regulated. The variable continuous potential applied to GR might be added to a fixed potential placed in series.

Figures 3, 4 and 5 represent modifications of the detector system.

The circuit arrangement of Figure 3 uses two bridge connected pentodes, two arms of the bridge being constituted by the internal resistances of these valves P1 and P2. The resistance couples RiRi, RzRz, R3R'3 and R4R4 are intended to make P1 and P2 as alike as possible for wide variations in the heating of the filaments and in the potentials applied to the anodes.

Across the terminals M and N of the primary winding of the transformer T1 there is applied the output potential of the filter and amplifier assembly AF of Figure 1. The transformer secondary winding comprises two symmetrical windings respectively connected to the grids G1 and G2. The alternating potential of the secondary winding 2 of Figure l is applied between the terminals C and D. Finally, a continuous potential proportional to the power delivered by the generator of ultra-short waves can be applied between E and F and regulation independent of the power is thus obtained, this feature supplementing the action of the device already described for this purpose.

The detected potential delivered between A and B is superimposed, by any usual means, upon the potential of the chosen electrode of the generator.

Figure 4 represents another modification; here the assembly comprises a pentode P which can be substituted for that of Figure l in the following manner: The extremity M of the input resistance .R: is connected to the output of the assembly AF; the secondary winding 2 of the transformer is connected across C and D in such manner as to apply the low frequency alternating potential of S to the second grid; the continuous potential proportional to the power given out, furnished by the second crystal K, is applied between E and F; finally, the anode is supplied with a continuous potential Ua, through the anode resistance 1. Again the condenser C2 is provided, for eliminating the alternating potentials and the conductor A connects the anode to the regulator electrode GB of the Klystron; the resistance R1 again serves to bias the cathode positively.

Figure 5 shows another modification in which the pentode P is substituted for the pentode of Figure 1. The differences as compared with the assembly of Figure 4 are simply the following: The potential of the source S connected between C and D is applied directly to the second grid, without interposing a resistance, but a continuous potential U is applied in series therewith; on the other hand, a capacity Cl is preferably shunted across the terminals of R1; the rest of the circuit is identical with the preceding one.

The invention includes another modification wherein the frequency supplied by the generator G of Figure 1 is itself modulated by any low frequency alternating source. In this case, modulation of the cavity may be omitted and there is only taken, from the said source, the potential to be applied to the screen grids of the pentodes of Figures 1, 4 and 5 and to the anodes of the pentodes of Figure 3.

It is to be understood that the various circuit arrangements above described constitute only non-restrictive examples and that details may be modified without departing from the scope of the invention. In particular, the detector systems comprising pentode valves could be otherwise constituted or replaced by any device sensitive to the simultaneous action of the alternating potential coming from the assembly AF and the potential of the same frequency coming directly from the source S.

I claim:

1. A device for generating ultra-short waves of stabilized frequency comprising in combination, an ultra-high frequency generator tube comprising a regulating electrode, a cavity resonator, means for supplying energy from the generator tube to the cavity resonator. an auxiliary source of low frequency energy, means for varying the resonant frequency of the cavity resonator in accordance with the frequency of the auxiliary source, a first detector and a second detector, means for supplying current from the cavity resonator to the first detector, means for supplying current from the generator tube to the second detector, filtering and amplifying means, means for supplying rectified current from both said detectors to said filtering and amplifying means, a third detector, means for supplying current to said third detector simultaneously from said filtering and amplifying means and from said auxiliary source, and means for supplying the output current of said third detector to the regulating electrode of said generator tube.

2. .A device according to claim 1, wherein the third detector comprises two pentode tubes and means for balancing each said pentode relatively to the other, said balancing means comprising adjustable resistances.

3. A device according to claim 1. wherein the third detector comprises two pentode tubes and means for balancing each said pentode relatively to the other, said balancing means comprising adjustable resistances, and wherein a direct current proportional to the output of the generator tube is fed simultaneously to one grid of each said pentode.

4. A device according to claim 1, wherein said third detector comprises a pentode having three grids supplied respectively with current from said filtering and amplifying means, from said auxiliary source and from said second detector.

5. A device according to claim 4, wherein direct current is supplied in series with the current supplied by said auxiliary source.

MARCEL DENIS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,404,568 Dow July 23, 1946 2,426,193 Fernsler Aug. 26, 1947

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