US2279441A - Ultra short wave generator - Google Patents

Description

Patented Apr. 14, 1942 UNITED STATES 2,279,441 ULTRA SHORT WAVE GENERATOR Kurt Buchmann and Harry Zuhrt, Berlin, Germany, assignors to Fides Gesellschaft fur die Verwaltung und Verwertung von gewerblichen Schutzrechten, m. b. H corporation of Germany Berlin, Germany, a

Application May 15, 1940, Serial No. 335,200 In Germany March 31, 1939 8 Claims.

This invention relates to an arrangement for varying the frequency of ultra-short wave generators with special iron variometers which permit of a variation of the effective permeability without substantial losses. This invention is particularly useful in decimeter wave radio systems. It is known that the frequency in the case of ultra-short wave generators depends on the electrical values of the oscillatory circuit as well as on the operating parameters of the tube.

Hence, for sharp tuning of the generator and for influencing the frequency of the oscillating generator at will, such as is necessary, for instance, in order to obtain a frequency modulation, two principal methods are available: firstly, to control the plate otential, and secondly, to control the action upon the circuit elements. Now, when changing the plate potential not only the frequency of the generator varies, but also its power. When attempting to realize a frequency modulation through a corresponding variation of the plate potential, the fact is that, owing to the power variations thereby encountered, there will always be produced at the same time an amplitude modulation. But this is usually not desirable. therefore, the variation of the plate potential as a means of influencing the frequency cannot be taken into consideration. Therefore, for certain purposes, the frequency of an ultra-short wave generator can best be controlled by varying the parameters of the circuit.

Now, the frequency of the generator may be determined by the action upon the resultant capacity or by the action upon the resultant in-' ductance of the oscillatory circuit. The present invention utilizes the method of varying the inductance of the oscillatory circuit, which method has the advantage of a purely electrical variation, as against the variation of the capacity which is always a mechanical variation.

It is known as such that the inductance of an oscillation coil having an iron core, and hence the frequency of an oscillatory circuit containing such an iron-core coil can be influenced by placing the iron-core in the field of an electromagnet whose field strength is being influenced by the intensity of the magnetizing current. The utilization of this idea for ultra-short wave transmitters has only recently been made possible by the development of ferrous which exhibit low loss characteristics when used in ultra-short wave systems. Yet it is still rather difficult to satisfactorily design an ultra-short wave generator having a suitable frequency determining circuit which includes a condenser and an iron core coil whose inductance can be varied,

because, as tests have shown, the power losses are unduly high.

Our invention eliminates this disadvantage for the first time and renders possible the tuning of an ultra-short wave generator to a definite frequency. Frequency modulation is also possible, not only with useful power but also with practically no power fluctuation. In carrying out our invention we preferably provide an arrangement in which one or several iron core coils are placed where they may be selectively switched into the circuit of the generator, or their positions may be adjusted so as to minimize the damping of the oscillatory ultra-short wave circuit. Means are also provided so that the preliminary magnetization of the iron core of these coils is variable.

In the drawing Figure 1 shows diagrammatically a preferred embodiment of the invention,

Fig. 2 shows a typical frequency-voltage characteristic curve as obtained when the generator of our invention is modulated, in comparison with such a curve as obtained without the use of an iron-core coil, and

Fig. 3 shows an alternative circuit arrangement with respect to Fig. 1.

Tests have shown that the losses due to the iron-core of the oscillation coil are of minor importance, if in the circuit which determines the frequency a coil 1 whichcontains iron is placed in parallel to a Lecher line 4, 5 as shown in Fig. 1. Here the condensers 8, 9 serve for separating the direct current. It is of particular advantage to arrange the coil 1 in the proximity of a voltage loop, because in this case the variation of the apparent resistance of the coil caused by the variation of the magnetic field has the greatest influence upon the frequency of the generator. In the event that the Lecher line is terminated by a condenser 5, it is advisable-to bring the coil as much as possible into resonance with this capacity. Therefore, a more or less loose capacitive or inductive coupling of the coil with the Lecher line is of advantage. This means of varying at will the magnitude of the influence.

Another possibility of connecting the coil is shown in Fig. 3, where the conductors 5 of the Lecher system between the limits aa and 12-h are the same as indicated in Fig. 1. In this case coil of the system Iiib is placed in suitably chosen section of the in- In order to provide symmetry the parallel to a dividual line,

also offers a simple:

apart the magnitude of the influence can be controlled. Hence the coil may also be placed directly into the current loop.

Since with the arrangement herein described comparatively wide frequency variations can be attained with comparatively slight power variations of the generator, the arrangement according to the invention is su'ted both for sharp tuning and for frequency modulation. In this case the modulation currents are utilized for the preliminary magnetization of the iron-core coil.

Then the frequency of the generator can be gov- From this erned by the magnetizing curent. there can be developed a method for maintaining constant the frequency while the anode potential fluctuates, in that the plate potential, or a potential derived therefrom so influences the magnetizing coil that the frequency variation brought about by the variation of the plate potential will be eliminated by a. corresponding variation of the inductance,

In addition to maintaining constant the frequency of an ultra-short wave transmitter, the

arrangement according to the invention can be utilized for the subsequent adjustment of the frequency of receivers, i. e., for the subsequent setting of the frequency of the oscillation tube of a superheterodyne receiver to a constant intermediate frequency, more especially at a varying transmitter frequency. The control is hereby carried out by a current which through circuits shown as such depends on the intermediate frequency being set.

In the case of frequency modulation, as well as when maintaining a constant frequency, and at the subsequent setting, aside from the actual control coil, a second winding for the preliminary magnetization may be utilized for the adjustment to the centra1 working point.v

In Fig. 1 item I designates an oscillation tube which at its grid 2 and anode 3 is connected to an oscillatory circuit consisting of a parallel wire line 4, 5 having the terminal condenser 6. The

iron-core coil 1 serving for varying the frequency is connected across the two condensers 8 and 9 which are, for instance, of the order of 10 i, to the parallel wire line for withholding the direct current or at the same time for suitable capacitive coupling. Through the coil H arranged on an iron-core ID, the magnetizing current can be passed which serves for varying the frequency,

hence, for instance, in the case of the frequency modulation the modulation current can be passed through, or in the case of the subsequent adjustment of the frequency of a superheterodyne receiver, a current can be passed through said coil which depends on the value of the intermediate frequency. The iron-core coil I prefer-- ably has only a few windings, for instance, three turns.

Fig. 2 shows the dependence of the amplitude upon the frequency variation. In this figure the curve a represents the amplitude variation at the frequency variation with the aid of an inductivity of an iron-coil in the arrangement according to the invention, while the curve I) shows the variation of the amplitude through the usual plate voltage modulation. This curve clearly in- 75 dicates that the amplitude decreases but very slightly which variations up to 1 megacycle in the arrangement according to the invention, while in the case of the plate voltage modulation the amplitude has decreased to a high degree within a range of about 300 kilocycles.

We claim:

1. Ultra-short wave apparatus comprising an oscillation generator having input and output electrodes, a Lecher wire system one conductor of which is connected to an input electrode and the other conductor of which is connected to an output electrode, means for controlling the frequency of said generator in dependence upon the resonance of said Lecher wire system,

said means comprising an induction coil wound on a low-loss core of magnetic material and coupled to points along said Lecher wire system where an optimum mutual reactance exists between the currents of said coil and said Lecher wire system, and means for varying the magnetic flux in said core.

2. Apparatus according to claim 1 and including capacitive means for coupling the circuit of.

said induction coil to the conductors of said Lecher wire system at points adjacent a voltage loop.

3. Apparatus according to claim 1 and including direct connections of said induction coil in parallel with one of the conductors of saidLecher wire system at points symmetric to a current loop oscillation generator having input and output electrodes, a Lecher wire system one conductor of which is connected to an input electrode and the other conductor of which is connected to an output electrode, an induction coil coupled across points of the two conductors in said Lecher wire system adjacent a voltage loop, said coil having a low-loss core of magnetic material, and means for varying the magnetic flux in said core, thereby to frequency-modulate said generator.

5. Ultra-short wave apparatus comprising an oscillation generator having input and output electrodes, 9. Lecher wire system one conductor of which is connected to an input electrode and the other conductor of which is connected to an output electrode, an induction coil parallel-connected to points on one of said conductors which are symmetric to a current loop, said coil having a low-loss core of magnetic material, and means for varying the magnetic flux in said core.

6. An oscillation generator in combination with from which tends to vary in frequencyas a function of the potential drop across its space discharge path, said frequency control means comprising an induction coil wound on a low-loss core of magnetic material and being provided with means for varying the magnetic flux in said '7. Apparatus according to claim 6 and lncluding a plurality of such induction coils each wound on a low-loss core of magnetic material and each connected to suitable points on said transmission line for influencing the resonant characteristic thereof.

8. An oscillation generator in combination with a two-conductor transmission line and means connected to said line and contributing to the 4. Ultra-short wave apparatus comprising an terial, the primary of said transformer being conductive of modulation currents and the secondary of said transformer being capacitively coupled to said transmission line at points adjacent a volt- KURT BUCHMANN. HARRY ZUHRT.

5 age loop.

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