DE1006904B - Mixing stage of an overlay receiver for the VHF range - Google Patents

Description

GERMAN

The invention relates to a mixer stage of a heterodyne receiver with a self-oscillating Mixing tube that works with additive mixing and is intended for reception in the VHF range is.

When using a directly heated triode as a mixer tube in such a circuit, e.g. B. for Suitcase receiver, it is very difficult to get a sufficient oscillator voltage, because the steepness of such mixing tubes is relatively high ring is. Furthermore, there is the difficult to meet requirement that when operating with dry batteries and the The very different voltages that occur in the process are still stable, even at the lower voltage limit Working of the oscillator is secured. Further, it is desirable that the difference in mixing gains when working with new or old batteries is as small as possible.

The invention provides a circuit which meets all of these requirements remarkably well. The invention consists in that, in the aforementioned additive mixing circuit, the oscillator circuit is connected in a capacitive three-point circuit between the three electrodes of the mixing tube, the receiving oscillation circuit (E) being between the neutral point of the oscillator circuit and the filament, and that the intermediate frequency circuit or at least the intermediate frequency coil is decoupled from the anode of this mixing tube by a high-frequency choke for the oscillator frequencies.

The two features relating to the oscillator circuit and the intermediate frequency circuit are known per se, namely with a mixed circuit for short waves, with self-oscillating triode with indirectly heated cathode, however, there is the receiving coil between the grid and the oscillator circuit, so that there is the requirement for the best vibration conditions is not met. Furthermore occurs, the receiving coil part of the oscillator voltage and can get into the antenna.

The explanation for the achievement of a high oscillator voltage when using the capacitive one Three-point switching lies in the following. Due to the tube capacities, there is already a capacitive Spanr voltage divider available. Therefore it is not favorable to use an inductive voltage division for the three-point connection to be used, because if two voltage dividers of different types are present at the same time, reaching the most favorable vibration condition is made more difficult. In addition, the connecting lines also play a role in the VHF range and cause unwanted phase shifts, can. If, on the other hand, only the tube capacitances are used as a voltage divider for the three-point circuit or you switch capacitors to the

a heterodyne receiver
for the VHF range

Applicant:

Telefunken GmbH,
Berlin NW 87, Sickingenstr. 71

Johann Stegmüller, Ulm / Danube,
has been named as the inventor

Add tube capacities (as close as possible to the tube), so you only have a single voltage divider, namely a capacitive one.

With such an oscillating circuit one would be in a self-oscillating mixer stage with a triode alone not yet achieve the highest possible oscillator voltage. Rather, it is necessary to use a capacitive Avoid loading the oscillator circuit through the intermediate frequency circuit because the additional Capacitance that occurs when the intermediate frequency coil is connected, the resonance resistance of the oscillator circuit, and not only because of the capacitance itself, but mainly this is because the losses of this capacitance are too great for the VHF oscillator circuit. This Be ^ Attenuation by the intermediate frequency coil is achieved by interposing a VHF choke (2/4 choke, that is, a choke that can be wound by winding a quarter-wavelength wire is avoided.

According to a development of the invention, particularly useful means for undamping the Intermediate frequency circuit can be used without affecting the amplitude of the oscillator oscillations, is affected.

The figure shows an embodiment of the invention.

The oscillator circuit O, the z. B. can be tuned by means of a rotary capacitor, is connected via the capacitors C ₃ and C ₄ to the anode and the grid of the mixing tube Ro . The capacitive three-point circuit is formed by the two capacitors C ₁ and C ₂ and the tube capacitances lying in parallel. In the line between the junction of the capacitors, C ₁ and C ₂ and

709.506 / 294

Earth, the receiving circuit E is switched on in order to avoid that the receiving circuit E carries the oscillator voltage and radiates it through the antenna.

The intermediate frequency circuit Z ₁ following the mixing tube is in this example formed by the inductances D ₁ , D ₉

and L ₁ and essentially, through the

Capacities C ₁ to C _{6 are} formed. The VHF choke D ₁ prevents the capacitances of the switching elements and lines lying to the right of it in the circuit diagram from lying parallel to the oscillator circuit O. A capacitor C _{5 is also} connected so that the oscillator voltage is only applied to the choke D _{1, if possible.} It was found that the. The bridge circuit formed by the oscillator circuit with the receiving circuit E in the diagonal is not in equilibrium over the entire receiving range, which is due to the fact that the coil ₁ for the oscillator frequency represents a highly frequency-dependent capacitance. By shunting the capacitor C ₅ , a practically fixed value of the capacitance is achieved.

In order to achieve undamping of the intermediate frequency circuit Z ₁ to eliminate the damping effect of the mixing tube, it is known to connect a capacitor between the capacitors at point P as a result of capacitive voltage division. C ₁ and C ₆ against. Earth occurring, intermediate frequency voltage to lead over the base of the receiving circuit E to the grid of the mixer tube. Tests have shown that a somewhat different damping circuit is useful in the circuit according to the invention. The capacitance of the capacitor C ₆ is dimensioned so large that it represents a short circuit for the intermediate frequency, so that at point P there is practically no intermediate frequency voltage. Rather, the intermediate frequency voltage used for attenuation is obtained by connecting point P to the grid of the mixer tube via a VHF choke D _2. Then form the inductances L ₁ and D ₂ , their. Connection point P is grounded in terms of intermediate frequency, an inductive three-point circuit, so that an intermediate frequency voltage serving for undamping occurs at the choke D _2. This choke D _{2 also} serves to block the oscillator voltage prevailing at the grid with respect to point P and thus with respect to earth.

If the throttle D _{2 is} dimensioned in such a way that the required blocking for the oscillator frequency is achieved, then, as experiments have shown, the intermediate-frequency feedback can become too great. To avoid this, the capacitance of the grid block capacitor C _{7 can be made} so small that the reactance of the choke D ₂ and the capacitance C ₇ together bring the desired value of the intermediate frequency voltage to the grid.

A circuit proposed by the Amnelderin can also be used as a capacitive three-point circuit in which to achieve the most favorable oscillation condition parallel to the capacitance on the anode side of the capacitive voltage divider a correspondingly dimensioned inductance is connected.

Claims (4)

PATENT APPLICATIONS: 1. Mixing stage of a heterodyne receiver with a directly heated triode as a self-oscillating mixer tube with additive mixing on the VHF range, characterized in that the oscillator circuit (O) is connected in a capacitive three-point circuit (C ₁ , C ₂ ) between the three electrodes of the mixer tube, with the receiving oscillation circuit (E) lies between the neutral point of the oscillator circuit and the filament, and that the intermediate frequency circuit or at least the intermediate frequency coil (L ₁ ) is decoupled from the anode of this mixing tube by a high frequency choke (D ₁ ) for the oscillator frequencies. 2. Mixer according to claim 1 with feedback for de-attenuation of the intermediate frequency circuit with the aid of a three-point circuit of the intermediate frequency circuit, characterized in that a high-frequency choke (D ₂ ) which blocks the oscillator vibrations is connected in the line leading to the intermediate-frequency feedback voltage to the grid of the mixer tube. 3. Mixer stage according to claim 2, characterized in that the throttle (D ₂ ) together with the coil (L ₁ ) of the intermediate frequency circuit forms part of the three-point circuit of the intermediate frequency circuit (Z ₁ ). 4. Mixer according to claim 3, characterized in that in series with the choke (D ₂ ) there is a grid _{block capacitor (C 7} ), the capacitance of which is dimensioned so that the reactance of the choke and grid block capacitor together, diq desired intermediate-frequency feedback voltage to that Grille brings. Considered publications:
German patent specification No. 739 095. 1 sheet of drawings © TO & 506 / 2W 4.57