LOW-FREQUENCY NOISE GENERATOR

A. M. MALYSHENKO, I. I. EFREMOV

(Presented by the scientific seminar of the Department of Automation and Telemechanics)

Generators of random signals (noise) are finding ever broader application each year in the simulation, on analog computers, of the motion of dynamic systems under the action of random disturbances, and for imitating the influence of the external environment during tests of finished systems. In such cases, noise generators are used for the artificial introduction of disturbances and for the formation of random processes with prescribed statistical characteristics.

Noise generators produced by domestic industry (GShN-1, LIG-24-48) have a uniform spectral density in the frequency range of about 50 Hz–30 MHz, and therefore their use in the study of dynamic systems possessing low-frequency filtering properties is limited. In particular, in studies of most automatic-control systems, generators of infralow-frequency noise are required, since only such disturbances exert a noticeable influence on the systems indicated.

At present a number of circuits of infralow-frequency noise generators are known. Most often they are based on the principle of heterodyning a random high-frequency signal [1, 2].

The infralow-frequency noise generator developed by the authors is based on the formation of noise with a narrow-band spectrum of low frequency (450–550 Hz) and its subsequent filtering by a nonlinear filter-limiter. According to [3], such a principle of constructing generators makes it possible to obtain a sufficiently powerful signal with uniform spectral density over a fairly wide portion of the infralow-frequency range. The schematic diagram of the generator developed is shown in Fig. 1.

As the noise element in the generator circuit, a thyratron TG-0.1/0.3 is used. The thyratron noises, amplified in the amplifying stage on tube L1, are passed successively through high- and low-frequency filters. The latter are connected with one another and with the other elements of the generator through cathode followers (L3, L4, L5). The narrow-band noise, after amplification by the amplifying stages (L6, L7), is fed to the nonlinear element-limiter (L9) and to the tunable low-frequency filter. Coupling between the indicated elements and the load is effected through cathode followers assembled on tubes L8, L10, L11. The generator is powered from DC voltage sources of +350 V and −190 V. The types of tubes used, and the ratings of the resistances and capacitances, are indicated in the circuit of Fig. 1.

The choice of the indicated supply-voltage values makes it possible, when the generator is used together with analog computers, to power it from the same power supplies as the machines.

Fig. 1. Schematic diagram of the noise generator

In particular, when the manufactured generator and the MNB-1 modeling unit were operated jointly, an electronic stabilized rectifier ESV-3 was used for these purposes. This feature of the generator power supply makes it possible, when necessary, to amplify the generated

noise could be used for these purposes by the analog computer’s operational amplifiers.

Tests of the developed generator showed that it is capable of generating a stationary random signal with an almost uniform spectral density over a range up to 5 cps. The noise generator constructed according to the described circuit successfully underwent tests over the course of a year and a half at the Department of Automation and Telemechanics and at the Research Institute of Nuclear Physics, Electronics, and Automation at TPI.

REFERENCES

1. N. M. Teterich. Noise Generators. Gosenergoizdat, Moscow, 1961.
2. Yu. M. Romanovskii. Low-frequency noise generator. Instruments and Experimental Techniques, No. 4, 1958.
3. Douce J. L., Shackleton J. M., L. F. Random—Signal Generator, Electronic and Radio Engineer, August 1958, vol. 35, No. 8, pp. 295—297.