DE1089017B - Oscillator circuit for superposition receivers in the frequency range of TV band IV - Google Patents

Description

GERMAN

The invention relates to an oscillator circuit, in particular a self-oscillating mixer circuit for receivers of television band IV.

1 shows a conventional oscillator circuit for the decimeter range, such as is used, for example, in attachments for television band IV and in particular for self-oscillating mixer tubes. It is a Colpitts oscillator in a grid-based circuit. The anode resonant circuit consists of the parallel connection of the grid-anode capacitance Cag and a 2/2 line 4 shortened on both sides by capacitors C ₁ and C ₃ arranged at their ends, which in principle acts as a coaxial line, with its outer sheath through the lines surrounding the line Chassis parts is formed. This line acts as an inductance that can be tuned _{by the variable capacitor C 1.} The end of the range can be set _{with the branch trimmer C 2} and the shortening _{tf always C 3.} The branch trimmer C ₂ is expediently applied to the line where there is a voltage node for the highest oscillator frequency in order to make the highest oscillator frequency independent _{of the setting of the trimmer C 2.} With a larger trimmer C ₂ , only the range after the lower frequencies is increased. The latter is very desirable if the tube is to work not only as an oscillator, but as a self-oscillating mixer for TV band IV, since in this case the capacitor C ₅ , which acts as a Tfennkondensator for the oscillator frequency and which serves as the oscillating circuit capacitance for the substantially low intermediate frequency, is also used should, must be kept relatively small and thereby narrow the area.

With this arrangement, the following difficulties arise: With certain settings of the variable capacitor C ₁ within the tuning range, the oscillator tends to oscillate at a higher frequency. The frequency-determining elements for this secondary resonance are the line section between the anode and the trimmer C ₂ , the capacitance Cag and the trimmer C ₂ .

It would be obvious to avoid such a spurious resonance by choosing the length of the said line section and the capacitance of the trimmer C _{2 to be} higher than the cut-off frequency of the tube used, for example above about 1200 MHz for the tube PC 86. However, this route cannot be followed for the following reasons:

The frequency range encompassing band IV is relatively large, it encompasses the frequencies from 470 to 790 MHz.

The secondary resonance frequency oscillator circuit located above 1200 MHz

for overlay receivers

in the frequency range of TV band IV

Applicant:
Standard electrical system Lorenz

Corporation,
Stuttgart-Zuffenhausen,
Hellmuth-Hirth-Str. 42

Hans Hein, Pforzheim,
has been named as the inventor

quenz f _N would be at least at one point of the oscillator tuning range around the intermediate frequency

^a 5 fzF 36 MHz higher than the receiving frequency, equal to twice the oscillator frequency / ₀ and at this point cause an unstable behavior, a so-called oscillation hole, of the oscillator.

For a tube working in a self-oscillating mixer circuit, fa must be less than / ^ + Z ₀ , because in the case where fe - fN ~ fo lsi> s * ⁰ * ^{1 the secondary resonance curve} would superimpose on the HF transmission curve and deform it.

For these reasons, a favorable secondary resonance point at around 930 MHz is chosen.

With the invention, a circuit arrangement is now specified with which with easily realizable Means

1. the switching of the oscillator frequency to the secondary resonance despite the relatively low secondary resonance frequency is avoided

2. the secondary resonance point can be shifted over the entire range without significantly affecting the oscillator frequency, without having to _{relocate the trimmer C 2} from the voltage node for the highest oscillator frequency and

3. at the same time a correction of the frequency response of the oscillator voltage, usually after the lower frequencies increases, is reached.

The invention is characterized in that a combined resistor is connected in series with the capacitor C ₉ , the inductive component of which does not significantly affect the resonance position of the secondary oscillation

009 607/258

Influence on the function of the capacitor C _2, which changes the line length, is fixed to a desired frequency, and its ohmic component serves to suppress the secondary oscillation.

The invention will be explained in more detail with reference to FIGS. 2a, 2b and 3:

2a and 2b show the circuit arrangement according to the invention;

Fig. 3 shows the practical embodiment of the circuit according to FIGS. 2a and 2b.

As can be seen from FIG. 2a, a parallel circuit 9Ϊ of an inductance 6 and a resistor 7 is connected in series _{with the trimmer C 2.} By choosing the inductance 6, the secondary resonance parts, which result from the line section from the anode to the trimmer C ₂ and through the trimmer C, can be set to a frequency at which it is least disturbing, without any noticeable influence to exercise the capacitance value of the trimmer 'C _{2 which is effective for much lower frequencies.} The resistor 7 attenuates the resonance circuit for the secondary frequency so strongly that the oscillator cannot switch to the undesired secondary frequency. Furthermore, it attenuates the oscillator voltage at lower frequencies, so that the frequency response of the oscillator voltage is corrected in general.

Instead of a parallel connection of an inductance and an ohmic resistor, a series connection 3t 'according to FIG. 2a could also be used. The parallel connection St , however, best reproduces the mode of operation of the practical embodiment shown in FIG. 3.

As can be seen from Fig. 3, a trimmer 10 is attached to the base plate 12, which corresponds to the trimmer C ₂ in FIGS. 1, 2a and 2b. The part 11 of the trimmer 10 which is at HF potential is connected to the line 4 via the brackets 8 and 9. The brackets 8, 9 represent the inductance 6. According to the invention, they are punched out in a simple manner together with the line 4 from a piece of sheet iron. The line 4 is silver-plated. Above the dashed line 13, however, the brackets are not silver-plated, so the sheet metal material appears there as a surface. The inductance 6 is thus attenuated by the very high losses on the iron surface as a result of the skin effect at high frequencies. Depending on the length of the non-silvered part of the bracket 8, 9, the damping is greater or less.

With galvanic application of the silver surface, the brackets can be kept free of silver, that they are previously dipped in masking lacquer up to line 13. The covering lacquer expediently remains on the temples as rust protection. The ends 15, 16 of the bracket are again silver-plated to a to allow easy soldering to the trimmer stator 11.

The influence of the inductance 6 on the oscillator frequency at the lower end of the range is minimal and can be compensated for _{by reducing the trimmer C 2 very slightly.}

Claims (4)

Claims = 1. Oscillator circuit for heterodyne receivers in the frequency range of television band IV, in particular as a self-oscillating mixer tube circuit, with a 2/2 line shortened by capacitors at the end remote from the anode and lengthened at the end near the anode by a branch capacitor as an oscillating circuit, which can be tuned by one of the shortening capacitors and in the the branch capacitor located at the end of the line near the anode in connection with the section from the tube anode to the capacitor gives rise to undesired secondary oscillations, characterized in that _{a combined resistor is connected in series with the branch capacitor (C 2} ), the inductive component of which is the resonance position the secondary oscillation without significant influence on the function of the capacitor (C ₂ ) which changes the line length, and whose ohmic component serves to suppress the secondary oscillation. 2. Oscillator circuit according to claim 1, characterized in that one or two wire brackets made of sheet iron, the surface of which is only partially silvered, are used _{as a series resistor for the branch capacitor (C 2) in the form of a trimmer.} 3. Oscillator circuit according to claim 2, characterized in that from the end of the trimmer (C ₂ ) which is not connected to the chassis, two partially silver-plated iron wire brackets extend to the line (4), which simultaneously support this mechanically. 4. Process for the production of an inductive series resistor for a Oscillator circuit according to Claim 2 or 3, characterized in that in the case of a galvanic Applying the silver plating to the surface of the iron wire hanger attach the hanger to the desired one Areas are kept free of silver by applying a masking varnish to these areas beforehand are provided, which also serves as a rust preventive. Considered publications:
German patent specification No. 452 662. 1 sheet of drawings © 009 607/258 9.60