3 Instruments of formation of standard measuring signals

Measuring generators - sources of signals of various shapes and frequencies, designed to work with radio engineering circuits. They have a number of fundamental differences from conventional generators: they have the ability to accurately set and adjust the output parameters of the oscillations (frequency, shape and voltage level or power) in wide ranges; they have high stability of parameters and built-in measuring devices, which allow to control the installation of signals; can work together with other measurement and program management tools. Depending on the shape of the output signals , measuring generators of harmonic, relaxation (pulsed) and noise oscillations are distinguished . The spectrum of the output signal of the harmonic oscillator has one or more harmonics. The output oscillations of the relaxation generator contain many harmonics with comparable amplitudes. The frequency range generators are divided into: infra-low-frequency (0.01 ... 20 Hz), low-frequency, or generators of the audio range (20 ... 300000 Hz), high-frequency generators (0.3 ... 300

MHz), microwave (microwave, over 300 MHz). A special group is represented by generators of random oscillations (signals) - measuring generators of noise signals. It is also necessary to note the generators of pseudorandom and linearly varying voltages (GLIN), which belong to relaxation generators. These generators use both measuring and scanning generators.

Regardless of the purpose, principle of operation and circuit design, the generator of any of the listed oscillations (except parametric generation schemes) consists of a non-linear amplifier, a positive feedback circuit and a DC power source. The shape and frequency of the output oscillations are determined only by the parameters of the generator itself.

The harmonic oscillation generator should contain a narrow-band oscillatory system. The principle of operation of the relaxation generators is based on charge-discharge or storage-absorption phenomena occurring in the broadband energy-intensive positive feedback circuits .

Consider the conditions of self-excitation of the generator of harmonic oscillations. For the excitation and generation of oscillations, a part of their power from the output of the amplifier (more precisely, from the oscillating system) is fed to its input along a specially entered positive feedback circuit (OS). In other words, such a device “excites itself” and is therefore called a self-excited generator.

Simplified mechanism of the occurrence of oscillations in the generator is interpreted as follows. When starting up in an oscillatory system, spontaneous free oscillations arise, caused by switching on power sources, surges of currents and voltages in the amplifying device, etc. Due to the introduction of a positive OS circuit, part of the oscillation energy from the amplifier output goes to its input. Due to the presence of a narrow-band oscillatory system, the described processes occur at one frequency ω and die out sharply at other frequencies. First, after switching on the generator, the amplification of the signal arising in the oscillatory system occurs in a linear mode, and then, as the amplitude of the oscillations increases, the nonlinear properties of the amplifying element begin to play a significant role. As a result, the amplitude of the output oscillations of the generator reaches a certain steady level and then becomes almost unchanged. The energy taken from the constant current source by the amplifier during one oscillation period turns out to be equal to the energy consumed during the same time in the load. In this case, they say about the stationary mode of the generator