DE1079123B - Arrangement for amplitude control of high frequency oscillators - Google Patents

Description

GERMAN

In general, the amplitude of an oscillator has hitherto been avoided in high-frequency technology to regulate directly, d. H. to change the oscillation state of the oscillator, as with previously known arrangements an impermissible frequency distortion occurs as a result and a regulation only in small Limits is possible. Attempts were made to circumvent these difficulties by using special rules and Separation tubes in addition to the high-frequency oscillator tube or resistance elements in special Rule arrangements are used. However, these represent permanent additional loads for the oscillating tube represent, which are to be kept as small as possible in oscillating circuits, because they are an additional extensive entail circuitry effort and the. The desired effect is also only very critical master is.

A generator is known whose amplitude is stabilized over a wide frequency range and in which there is a tendency towards over-feedback and the known periodic interruption of the vibrations is suppressed. This is achieved by the fact that when the amplitude increases, the vibrations generated an additional, supporting the effect of the already existing grid capacitor charge Charge of a capacitor lying in the lattice circles is generated, with a two-electrode tube in parallel is connected to the grid-cathode section of the transmitter tube and the anode of the two-electrode tube connected to the grid of the generator. In this way a charge balance is kept constant generated by the generator amplitude.

Also in the circuit technology of .RC generators, - d. H. Oscillator stages that use only ohmic resistors or capacitors for the purpose of tuning - It is known that a device for limiting the amplitude must be provided, for example by means of Two-pole rectifiers whose base point is at the cathode potential of the generator tube.

Finally, modulation arrangements, in particular for the ultra-short wave region, are known. where oscillator oscillations corresponding to the potential at the anode of a diode more or less are cut off as soon as the threshold value of this diode is exceeded. Only one very small time constant.

The invention, however, relates to a direct control of the amplitude of a high frequency oscillator by means of a control voltage by this control voltage in a series circuit is supplied to the control grid of an oscillator tube in the form of variable grid bias voltage in such a way that a rectifier path parallel to the grid leakage resistor is on the anode side of the control grid while it is arranged for Amplitude control
of high frequency oscillators

Applicant:

SABA

Black Forest Apparatus Construction Company

August Schwer Sons G. m. B. H.,

Villingen (Black Forest)

Dr. rer. nat. Hansridiard Schulz, Villingen (Black and White), has been named as the inventor

ao on the cathode side together with the one facing away from the grid side The end of the bleeder resistor is DC-wise at the potential of the control voltage and is held at the potential of the oscillator cathode in terms of high frequency via a blocking capacitor, the internal resistance of the control voltage source and the blocking capacitor being a member of a large time constant form,

It is then attached to the vibrating grid, e.g. a triode as a high-frequency oscillator, via a dem Grid leakage resistor in parallel rectifier path, z. B, tube rectifier, or germanium diode, or via a transistor, a control voltage is supplied, whereby a continuous amplitude control of the oscillator is made possible in a very simple manner. This allows a generator amplitude to be controlled directly, i. i.e., with others Words one can arbitrarily change the oscillation state of the oscillator without a disadvantageous one Having to accept frequency utilization. It continues with the arrangement according to the invention reaches the oscillator ampUtude in a very wide range of at least two powers of ten to change, with the oscillator voltages in areas of 1 volt eff. and move smaller. The so far known means for this - z. B, special control or Tren tubes or special control resistor elements - on the other hand, allow regulation within only small limits and result continuously for the generator additional adverse burdens.

In an expedient embodiment of the invention, it is used to increase the usable control range of the high-frequency amplitude the fundamental wave of the oscillator as a subharmonic of the one taken from the oscillator High frequency oscillation formed.

909 7W365

There are known amplitude modulation arrangements which are based on the direct limitation of the oscillator amplitude based on diodes, in which the use of electricity is shifted by the modulation voltage will. Simultaneous grid voltage modulation by applying an in-phase modulation voltage The purpose here is the control power required for diode limiter modulation to belittle. With this combined diode and grid voltage modulation, however, the diode limiter modulation must be used predominate, because otherwise the grid-cathode route of the oscillator tubes and the Limiter diodes are blocked in the event of negative modulation half-waves. Would you get an in-phase there Apply modulation voltage with the same amplitude, then the diode is for oscillator voltages, whose positive peak value at the anode is less than the positive cathode bias, blocked, and no limiting effect can occur. In this case, the only one that reaches the grid of the oscillator tube Modulation voltage then blocks the rectifier path in its negative half-oscillation Cathode — grid of the oscillator tube and creates a Breaking off the vibration. In this case, the operating state assumed to be known occurs, as it is dealt with in an example according to FIG. 1 below.

However, the principle after registration does not work deliberately with a direct limitation by the Cut off oscillator oscillations after exceeding a setpoint, rather it is based on the Effect of a non-biased peak rectifier in the form of a diode with parallel high resistance Leakage resistance, with the diode cathode common to the control voltage potential with the bleeder resistor and the grid-cathode path blocked in the case of a negative control voltage of the Oscillator tube for generating the necessary to maintain a stable oscillation, the oscillator amplitude is replaced by a negative direct voltage between grid and cathode proportional to the oscillator amplitude.

The essence of the invention is based on exemplary embodiments described in the figures. It shows

Fig. 1 shows the known design for high-frequency oscillators and

Fig. 2 associated tube characteristic with representation of the course of the oscillator voltage U ₀ as a function of the grid bias voltages,

Fig. 3 shows an arrangement according to the invention

4 shows the associated characteristic curve U ₀ as a function of the bias voltage U _v .

In Fig. 1, the triode 1 is shown as a high-frequency oscillator in a so-called Colpitts circuit, ie in a capacitive three-point circuit in a known manner. The three-point formation is carried out by the capacitors C ₁ , C ₂ and C ₃ , while L denotes the inductance of the resonant circuit. The anode voltage U _a is supplied via the resistor R ₁ . Is regulated _v in this known arrangement, · the oscillator by means of a variable bias voltage U - whose internal resistance, · has a high impedance with 2 indicated - by (+) is grounded and (-) supplied via the leakage resistance R _a of the control gate 2 of the triode 1 control 4 of the oscillator voltage U ₀ is obtained in the associated characteristic curve according to FIG. 2 only over a relatively small area 3 of the grid bias voltage U _v . Beyond a certain limit value 5 of the bias voltage U _v , the oscillator oscillation breaks off and the oscillator voltage U _v jumps to the value "zero". In Fig. 1, the capacitor C _{4 is provided} for high-frequency bridging of the bias voltage source U _v .

The cause of such discontinuous behavior of known oscillator amplitude control is that in In these circuits, the rectifier path grid - cathode with the amplifier - d. H. Oscillator tube inevitably has the same cathode, so that the foreign

ίο on the control grid, e.g. B. via the bleeder resistor K _a , supplied control DC voltage acts as a reverse voltage for the rectifier path. In order to maintain a stable, steady state of oscillation, the alternating control voltage of the oscillator must in any case increase up to the point at which the grid current starts, ie up to the area of effective rectification. However, I can do this as long as the feedback condition is met, ie as long as the effective slope of the oscillator tube does not fall below a certain limit value for a given constant feedback factor. Since, on the other hand, the effective slope is a function that tends towards zero with increasing negative DC control voltage, there is a limit value for the control voltage which, when exceeded, can no longer satisfy the feedback condition required for modulation up to the grid current, so that the oscillator oscillations have to stop.

In Fig. 3, however, the novel arrangement according to the invention is shown, which enables continuous regulation of the oscillator voltage U ₀ over a large range. In FIG. 3, the same switching elements of FIG. 1 are provided with the same reference numerals. According to the invention is now, but parallel to the bleeder resistor R _a , z. B. a germanium diode 6 is connected, the cathode of which is connected to the base of the resistor R ₁₁ and is connected to ground via a capacitor C _{4 in} terms of high frequency.

The oscillator according to the invention differs in a novel way from known control circuits - z. B. according to Fig. 1 - in that amplifier and limiter parts are separated. While the amplification is taken over by the triode I as before, the amplitude limitation through rectification effects an additional diode connected in parallel to the grid leakage resistor R _{a of} this triode 1, i.e. a tube section with at least one grid or an equivalent germanium diode 6 or a transistor, the cathode of which is then connected to ground together with the base of the grid discharge resistor R _a via a capacitor C ₄ , viewed in terms of high frequency, while the cathode of the diode path 6 is at the potential of the control voltage in terms of DC voltage.

One such according to the invention in the exemplary embodiment 3 connected diode 6 is in contrast to the rectifier path grid-cathode of the Triode 1 from the negative. Control voltage not locked. The entire DC control voltage on the Triode 1 is the sum of the control DC voltage and the also negative rectified DC voltage of the Diode-6. The control DC voltage changes the effective The steepness of the triode 1 and thus the oscillator amplitude, while the rectified direct voltage corresponds to the associated stable working point determined. According to this, the oscillator amplitude can be determined by a "high resistance" Regulate negative DC voltage continuously, in a wide range, such as the characteristic

10

line drawing of Fig. 4 identifies. In addition, the oscillator frequency is not detuned because the total DC voltage at the oscillator grid and thus the grid capacitance over the entire control interval changes little.

An oscillator stage built in the frequency range of 200 MHz according to FIG. 3 with the triode part of a tube of the PCF 82 type, 8 pF each _{being used for capacities C 1} , C _{2 and C 3} = 15 pF and C ₄ with 80OpF , for example, with a leakage resistance R _a = 50 KOhm and a parallel-connected germanium diode 6 of type RL 31, results in an oscillator amplitude control over two decades only an imperceptible oscillator detuning significantly below 1% (per mille). The arrangement according to the invention therefore makes it possible to change the high-frequency amplitude of an oscillator within wide limits without detuning the frequency.

Such arrangements are of particular importance for oscillator control in heterodyne receivers, because with extremely little circuit effort, and precisely by regulating the high-frequency amplitude on the most favorable value for the mix, especially in the VHF range, the possibility arises that to effectively limit interference radiation that is well-known and previously only had to be suppressed with great effort.

An arrangement according to the invention can prove to be particularly advantageous if, when the high-frequency amplitude is controlled, the fundamental oscillation of the oscillator is formed as a subharmonic of the controlled high-frequency oscillation desired for the mixing process. The fundamental oscillation is thus shifted to the »th subharmonic of the desired frequency. Since harmonics are essentially generated by yi rectification on the anode current (J ₀ ) grid voltage ([7 _g ) characteristic curve of the oscillator tube, the amplitude of the «th harmonic is a first approximation of the η th member of the Taylor series of these The characteristic curve is proportional to the operating point under consideration, and in comparison to the fundamental oscillation, the «• th power of the control range of the fundamental oscillation results for the« th harmonic.

So if you regulate with such a trick z. B. the fundamental of the oscillator over a power of ten, so at the same time z. B. the 3rd harness regulated over 3 powers of ten. It follows from this a control option - advantageous z. B. for mixing stages in heterodyne receivers - in each desired dimensions, whereby by shifting the fundamental oscillation of the mixer stage into Area of a subharmonic and, through simultaneous amplitude control, the interference radiation in the areas of the high-frequency area used for reception purposes is completely prevented.

Claims (2)

PATENT CLAIMS: 1. Arrangement for regulating the amplitude of a high-frequency oscillator by means of a control voltage, characterized in that this control voltage in a series connection to the control grid (2) of an oscillator tube (1) in the form of variable grid bias (£ / _v ) is supplied in such a way that a Laid parallel to Gitterableitwiderstand (R _a) rectifying section (6) is located on the anode side to the control grid (2), while the cathode side along with the grid-side end facing away from the leakage resistance (R _a) direct current at the potential of the control voltage and for high frequency through a blocking capacitor (C ₄₎ is held at the potential of the oscillator cathode, the internal resistance of the control voltage source (R ₁ ) and the blocking capacitor (C ₄ ) forming a member of a large time constant. 2. Arrangement according to claim 1, characterized in that the fundamental oscillation of the oscillator as a subharmonic of the oscillator removed high frequency oscillation is formed. Considered publications:
German Patent Nos. 892 609, 892 610;
Swiss Patent No. 209 048;
Radio Mentor, July / August 1944, pp. 160 to 164. 1 sheet of drawings © ι 909 769/565 3.601