DE1286635B - Transistor oscillator for feeding a coaxial comparator for two-pole and four-pole measurements - Google Patents

Description

The invention relates to a circuit arrangement for generating the high-frequency signal voltage that is used in measurements with coaxial comparators in the VHF and UHF area is required.

Comparators with rotatable inductive loops are known in which a known input variable (current, voltage) is fed to the quadrupole and the output current is compensated for by known active and reactive currents, separated into active and reactive components. To represent the known currents, a separate generator feeds three inductive coupling loops with the same phase and amplitude, which induce voltages via slots in adjacent coaxial conductors, the magnitude of which depends on the angle of rotation of the loops. The currents in the coaxial conductors depend on the resistances at the end of the lines. These are formed by an active standard (ZL), a blind standard (± jZL) and the desired transmission parameter of the quadrupole. To determine the four-pole parameter sought, the loop over the active line and the loop over the stub line are moved until the voltage at the four-pole output is zero. The parameter sought can then be determined from the angular positions of the loops. The loop above the four-pole line is used to set constant factors by which the measuring range can be expanded. In order to transform the voltages induced in the coaxial lines or the currents proportional to them directly to the four-pole terminals, 1/4 or A / 2 lines or corresponding multiples thereof are used.

With the two-pole measurement according to the same principle, the generator feeds also three inductive coupling loops, which have slots in three neighboring ones Coaxial conductors induce voltages. The coaxial conductors are in a compensation point merged and switched to a zero indicator. The other ends of the coaxial conductors are once with an active standard, a blind standard and a two-pole or input or output terminals of a four-pole terminal. The Determination of the two-pole parameters, separated by active and reactive component by turning the loops over the active and the blind branch, until the voltage in the compensation point Zero prevails. The loop above the measuring branch is used to set a factor to extend the measuring range.

There are also comparators for determining two-pole parameters known to have only one purely inductive loop across the node of three Coaxial conductors with an active standard, a variable blind standard and the test object are completed, is rotated. If there is zero voltage at the node, then the position of the loop and the size of the blind standard can be used to determine the one you are looking for Determine two-terminal parameters.

To expand the measuring range, it is known instead of the one used simple loops to use so-called double loops. These double loops consist of a series connection of two simple inductive loops, which but can be set separately. By using such double loops, Extend the measuring range to a range from 0.01 ZL to 100 ZL. The measuring range extension is effective separately for active and reactive components.

Numerous types of oscillator for the meter and decimeter wave area are known in which LC circuits, butterfly circuits or line circuits are used as frequency-determining elements. The high-frequency energy is decoupled inductively or capacitively from the circuit. When using conventional VHF or UHF transistors, the available voltage is around 100 ... 500 mV at 60 ohms. If transistor oscillators are to be used to feed coaxial comparators, the following disadvantages arise: 1. The available signal voltage is not sufficient, especially in the meter wave range, since the attenuation of the inductive coupling points used in comparators increases by 6 db / octave towards lower frequencies.

2. Since the comparator input for the oscillator is a pure reactive load the oscillator is severely detuned. If they are firmly connected, they tear Vibrations.

These two disadvantages include the use of transistor oscillators for feeding comparators almost off.

The purpose of the invention is to avoid these disadvantages and a to propose extremely cheap solution for feeding a comparator.

The invention is based on the object of a circuit arrangement a transistor oscillator using commercially available low-power transistors to propose to feed a comparator.

According to the invention the object is achieved in that the short-circuited Lines of the primary branch of the comparator measuring head via a short line fixed or variable length with a variable or fixed capacitor to one Line circuit are interconnected, which is the frequency-determining element of a Transistor three-point oscillator forms. This way it becomes an inductive or capacitive decoupling avoided, and the full reactive current of the oscillator circuit flows through the coupling loops of the comparator.

The variable capacitor is used to achieve a wide frequency range designed so that when the capacity is increased, an extension at the same time the line length between the capacitor and the comparator junction and thus a Enlargement of the inductance is achieved.

In a further development of the invention it is provided that the frequency-determining Line and the capacitor is designed as an outer conductor with a piston, wherein the piston coaxially surrounds the inner conductor, which is partially as a helical line is performed by a tubular grinder located inside the piston is partially short-circuited in the longitudinal direction and the outer jacket of the piston with the inner sheath of an outer conductor represents a variable capacitance.

With the circuit structure described, it is now possible under Use of cheap low-power transistors for measurements with comparators Required VHF or UHF signal with sufficient amplitude and high frequency constancy to create. Since the oscillator and the comparator measuring head form a unit, they are not required the usual measures to prevent interference radiation. The manufacturing cost of the oscillator described are a maximum of 25% of the usual costs. in the The following exemplary embodiment is intended to illustrate the invention with reference to two figures explained.

F i g. 1 shows an embodiment of the circuit arrangement according to the invention in connection with the measuring head of a double loop comparator. For simplification only the inner conductors of the coaxial lines are shown. The three-armed branching line 1 in the measuring head of the comparator is connected to the cylinder capacitor via a coaxial adapter 2 3 interconnected to form a management group. This forms with the transistor and the two trimmer capacitors 4; 5 a three-point oscillator. The desired frequency range is by appropriate choice of the electrical length of the intermediate piece 2 and the The capacity of the cylinder capacitor 3 is set.

F i g. 2 shows an embodiment of the principle of the used Cylindrical capacitor.

The outer conductor 6 and the tuning piston 7 form the linings of a Cylindrical capacitor, the capacitance of which depends on the length a. The inner conductor 8 is partially designed as a helical cable. This helical line is through the tubular grinder 9, which is connected to the tuning piston 7, partially short-circuited.

When the length a is increased, the effective length becomes the helical cable enlarged. However, this corresponds to an increase in the effective ones Inductance.

Claims (2)

Claims: 1. Transistor oscillator for feeding a coaxial comparator for two- and four-pole measurement, characterized in that the primary branch of the comparator measuring head via a line of variable or fixed length with a fixed or variable capacitor to a line circuit and this with an HF transistor and two capacitors are interconnected to form a three-point oscillator. 2. transistor oscillator according to claim 1, characterized in that the frequency-determining line and the capacitor is designed as an outer conductor (6) with a piston (7), wherein the piston coaxially surrounds the inner conductor, which is partially designed as a helical cable by a tubular grinder located inside the piston (7) (9) is partially short-circuited in the longitudinal direction and the outer jacket of the piston with the inner sheath of an outer conductor represents a variable capacitance, such that that by moving the piston line length and capacity increases at the same time or is reduced.