Measuring Generator

an instrument that generates low-power electrical oscillations for testing and tuning radio-engineering devices; it is used chiefly as an AC source over a broad frequency range. The main requirements for a measuring generator are stability of frequency and amplitude of the oscillations being generated, constancy of output-signal shape over the entire frequency range, careful shielding of the instrument to prevent its internal electromagnetic fields from affecting the apparatus being tuned or tested (signals from the measuring generator most often are supplied along a coaxial or shielded cable, as well as along a wave guide). Measuring generators have various designs and schematic diagrams, depending on the type of signal (sinusoidal, pulse, and special shapes) and the range of frequencies being generated.

Low-frequency (audio) generators. Low-frequency generators are used mainly for tuning and for determining the technical characteristics of low-frequency circuits, subassemblies, and elements of radio receiving and transmitting devices and as external modulators of signal generators and power supplies of measuring instruments, as well as for calibrating frequency meters and other devices operating in the frequency range of 20 hertz (Hz) to 200 kilohertz (kHz). The output signal of a low-frequency generator can vary smoothly or stepwise from 0.1 millivolt to 150 volts in voltage, and up to 5 watts in power, with a coefficient of nonlinear distortion less than 1 percent. Low-frequency generators are simple in design and stable in frequency and can be continuously regulated over their whole range.

Standard-signal generators. A standard-signal generator most often is a source of sinusoidal electrical oscillations. All parameters of the output signal of a standard-signal generator (frequency, amplitude, power, voltage, and type and intensity of modulation) can vary over a broad range, but their values are precisely determined for each tuning position. Depending on the range of generating frequencies, standard-frequency generators are divided into ultralow-frequency generators (from 50 microhertz to 1000 Hz), for testing and regulation of automatic tracking systems, electronic analogues, and other apparatus that operates in this range; generators of sonic and ultrasonic frequencies (from 20 Hz to 200 kHz), for calibration and regulation of communications and hydroacoustic apparatus; high-frequency generators (100 kHz to 100 MHz), for testing and tuning communications and television receiving and transmitting equipment; and ultrahigh-frequency generators (100 MHz to 80 gigahertz [GHz]), for testing, tuning, and regulating radar and other radioelectronic ultrahigh-frequency apparatus. Standard-signal generators are equipped with modulators of various types (amplitude, frequency, or pulse); in addition, they may be modulated by an external source. The output signal of a standard-signal generator is voltage-regulated in a range from fractions of a microvolt to 1 V and power-regulated in a range from fractions of a picowatt to several milliwatts.

Signal generators. Signal generators differ from standard-signal generators mainly in their larger output capacity (up to several watts) and in their lower precision of frequency gradation. They are used as sources of high-frequency electrical oscillations in testing and tuning radio-engineering devices. A variety of signal generator is the sweep generator, which is intended for visual tuning of oscillating circuits, filters, and amplitude-frequency characteristics of radio apparatus in the range from low to ultrahigh frequency.

Video-frequency generators. Video-frequency generators are used to study and tune ultrashort-wave systems, FM broadcasting systems, and television and communications systems and for checking discrimination circuits. Their construction is analogous to that of low-frequency generators; their essential difference is a wider range of generating frequencies, which attain a maximum value of 30 MHz.

Pulse generators. Pulse generators are used extensively in radar and computer technology, in tuning and testing radio-engineering and radio-electronic apparatus, and for measuring time and simulation of nonperiodic and random processes. There are several varieties of pulse generators, which differ in their repetition frequency (0.1 Hz to 100 MHz), pulse width (1 sec to 10 nanosec), on-off time ratio (from 2 to 1000 and higher), and shape of the oscillations generated (rectangular, peaked, sawtooth, and so on), as well as pulse-packet generators (code-pulse generators). Pulse generators may be single-channel (one output) and multichannel (two or more outputs) with different polarities and output-signal levels; as a rule, they have step adjustment of pulse width and continuous regulation of their periodicity.