DE1026800B - Input circuit of a VHF overlay receiver - Google Patents

Description

In applied high-frequency technology, cables take over the energy transport, as in high-voltage technology. But with a shorter wavelength, the lines themselves become independent elements of high-frequency technology. Therefore, efforts are made to make the lines as short as possible ^one, because, not only the electrical. The values of the lines play a role in the functioning of the overall circuit in such a way that, for example, the values of the coils provided must be changed, but since the lines have a radiation resistance, i.e. an antenna effect, if the wavelength is sufficiently short, these lines start to radiate high-frequency energy and / or record.

It is therefore important to avoid harmful emissions in heterodyne receivers with an ultra-short wave range of the oscillator, with regard to the bottom and top walls, otherwise the Oscillator interference voltage already on lines that approach the oscillator frequency or one of its Harmonics are matched, comes to abstraction. This phenomenon is particularly serious for VHF mixers without a high-frequency preamplifier tube.

The structure, mode of operation and disadvantages of a conventional receiver circuit will be described with reference to Fig. 1. The input circuit L _{1 is} C ₁ is C _{4 3} ', L ₃ ", the oscillator circuit L ₂ C ₂ gelegt.DieUKW-Abstimmkondensatoiren are connected to the balanced with respect to the points A and K by, C ₃ feedback winding L of the! Commonly used for radios to, a unit in a tub in common with the tuning directors for amplitude modulation. The result is that strong currents, originating from the VHF oscillator, cross the rotor axis partly through the mass of the VHF pre-circuit to the chassis Circles are unipolar on the chassis, with the usual arrangement according to Fig. 1, due to C ₄ and the coupling via the rotor axis and ground lug of the input circuit, compensation of the potential difference of the oscillator wave or its harmonics is made possible, and a correspondingly strong radiation occurs the antenna connected to the input circuit.

Care must therefore be taken that the oscillator oscillations and their harmonics do not have an effect as interference voltage via the axis of the variable capacitor and via the coupling capacitor between the input and oscillator circuit in the antenna circuit. It is difficult to make VHF equipment that complies with the regulations for oscillator broadcast without losing too much sensitivity. Other devices have input circuitry
an FM heterodyne receiver

Applicant:

Dipl.-Ing. Heinz-Fritz Reichenkron,
Baden-Baden, Herrengut 6 b

Dipl.-Ing. Heinz-Fritz Reichenkron, Baden-Baden,
has been named as the inventor

additional suction circuits. Except for a higher, technical one and economic expense of the arrangement shown is associated with the disadvantage that

ao too; the reception performance is reduced.

In contrast, the invention is based on. a line from the connection between the high-frequency input circuit, and grid circuit of a self-oscillating Trio diene mixing stage, which in addition to ^one optimum high-frequency transmission and optimum freedom from interference, and therefore fulfills the following functions:

1. The line provides the transmission path for the received oscillations: from the input circuit to the Grid of the mixer tube. The line is adjusted to the receiving frequency by means of a series capacitor Voted. With the help of this series resonance circuit, the received voltage is transformed reached towards the mixing grid.

2. Several measures are used to compensate for that which has still reached the input circle Part of the oscillator vibrations reached.

These measures consist in that the connection point of the series capacitor to ground and also the sense of coupling and the degree of coupling of the line coupling coil with the input circuit as follows be chosen so that the rest of the oscillator oscillations are canceled.

These functions are fulfilled by a transmission line which has an inductive coupling with the high frequency Has input circuit by means of a coupling coil, a connection of the coupling coil via a to Matching the line variable capacitance to ground, while the other connection of the Coupling coil via a piece of line to a tap on the grid circuit inductance of the self-oscillating Triode mixing stage is performed.

The effect of the arrangement is explained on the basis of FIGS. 2 and 3.

7 »9S7 / 304

Fig. 2 shows the circuit of the entire mixer while

Fig. 3 shows the line together with the high frequency input circuit.

The high-frequency input circuit L ₁ C ₁ is coupled to the transmission line via the coupling coil L _4. The coil L ₄ is on the one hand _{in a conductive connection with the variable capacitance C 5} , on the other hand via a line piece to the input A of a bridge circuit symmetrized with respect to the cathode of the self-oscillating triode mixer. The bridge circuit is "formed in known manner by means of the coil L ₃ 'and L ₃ of the tube capacitance between grid and cathode and! The variable capacitance C _3. By means of this bridge circuit is gear with respect to the oscillator voltage of the SETUP A placed at cathode potential. As a result, only a small component of the oscillator voltage access the input circuit. on the other hand, the path for the high frequency input voltage a is released to the grid. the variable · capacitance C _5, the line is matched. with the coil L ₄ is the coordinated transmission to the high-frequency. input circuit L adapted ₁ C _1. Where appropriate, with the aid of an additional inductance, as a further voltage increase z. a coil L ₅ according to Fig. 3, instead. from Brüclcenieingang ^! of view, the oscillator residual stress in the direction is reduced to the input circuit by voltage division .

The position of the base point of the changeable capacitance C ₅ is decisive for the extent to which the oscillator vibrations are emitted. It is expediently chosen on the chassis.

The measures indicated lead to the Emission of this mixer stage without pre-tube at least the same low values in terms of of the fundamental waves, reached like a mixer with a high-frequency preamplifier tube. With regard to the With such an arrangement it is possible to obtain lower harmonics than with one Mixer stage with high-frequency preamplifier tube, which via the coupled electrodes, capacitive paths, mainly for the harmonics, leaves open.

Claims (2)

Patent application; 1. Input circuit of a VHF heterodyne receiver without pre-tube using a self-oscillating triode as a mixer tube, in which the received vibrations are taken from the input circuit via an inductively coupled transmission line, and a tap of the grid circuit inductance of the mixer tube, characterized in that the transmission line with the help of a _{series capacitor (C 5} ) lying at the input end is matched to the received oscillations, that by selecting the connection point of the series capacitor (C ₅ ) to ground; and by choosing the sense of coupling and the degree of coupling of the coupling coil (L ₄ ) belonging to the line with the input _{circuit (L 1} C ₁ ), a compensation is achieved for the part of the oscillator oscillations that has entered the input circuit. 2. Input circuit according to claim 1, characterized in that an additional inductance (L ₅ ) is switched on in the transmission line between coupling coil (L ₄ ) and tap (A) of the grid circuit inductance. Considered publications: Swiss patent specification No. 158 091; British Patent No. 450272; Radiotechnik, 1953, p. 95, Fig. 5. 1 sheet of drawings ® 709 957/304 3.58