Refinement of the generator Electronics GIS-02T. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Television, video equipment

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While testing a digital radio relay line, the author encountered the fact that the standard test signal generator "Electronics GIS-02T" does not allow working with it in full. To complete it, it was also necessary to use sound signal sources, for example, televisions, which caused certain inconveniences in testing and reduced their quality. The proposed device eliminates this disadvantage by expanding the functionality of "Electronics GIS-02T".

The upgraded generator of test signals "Electronics GIS-02T" with PAL encoder [1] was successfully used for repair and adjustment of television equipment. But this generator generates only test video signals, which are not enough for operation - sound ones are also needed. Therefore, the idea arose to expand its functionality by adding a sinusoidal sound signal generator.

Main Specifications

• Supply voltage, V ....... 9
• Generation frequency, kHz ....... 1
• Output signal swing, V ...... 1,5

To power the sound signal generator, the internal supply voltage of "Electronics GIS-02T" was used, as in the previous revision described in the article [1]. The output voltage of 1,5 Vp-p is sufficient to set up both new digital and old analog radio relay lines. The frequency of 1 kHz was chosen because it is customary on television to record a test program before starting video recording: an image and a sound tone of 1 kHz, so directors, sound engineers, cameramen and engineers are used to this frequency.

Rice. 1 (click to enlarge)

The sound generator circuit is shown in fig. 1. An amplifier is assembled on a transistor VT1 according to a circuit with a common emitter, on a transistor VT2 - an emitter follower. To excite oscillations in the feedback circuit between the emitter of transistor VT2 and the base of transistor VT1, a double T-bridge R1-R3C1C2C4 is included, which provides generation at a given frequency [2, 3].

Trimmer resistor R5 achieve a sinusoidal waveform on the load of the transistor VT2 - resistor R6.

An amplifier is assembled on the VT3 transistor, which is insensitive to temperature fluctuations and allows the replacement of the transistor without its selection. Stabilization of the operating mode is achieved due to direct current feedback [4, 5].

Fig. 2

Most of the generator parts are placed on a printed circuit board made of one-sided foil fiberglass. The drawing is shown in fig. 2 The board is placed in the "Electronics GIS-02T" case, and on its rear panel there is an R13 output signal swing regulator and an XW1 connector - an RCA "tulip" socket.

Transistors VT1-VT3 - any of the KT315 series. Capacitors C1, C2, C4 - ceramic, C3, C5, C6 - imported oxide. Fixed resistors - MLT 0,25, trimming resistor R5 - SDR-386, variable R13 - SPO.

To establish the proposed device, only an oscilloscope is needed. Before applying the supply voltage, set the engine of the tuning resistor R5 to the lower position according to the diagram and connect the input of the oscilloscope to the right output of the capacitor C5 according to the diagram. Then turn on the power and move the trimmer resistor R5 until generation occurs. Its further movement achieves a sinusoidal waveform. If even in the lower position of the engine according to the scheme, the shape of the generated signal differs significantly from the sinusoidal one, the negative feedback in the generator is increased, including a constant resistor in series with the tuning resistor R5, the resistance of which is selected experimentally. After that, the oscilloscope is connected to the negative terminal of the capacitor C6 and the output signal swing is set to 1,5 V by selecting the resistor R8. If its resistance is reduced to zero, and the required range is not reached, reduce the resistance of the resistor R12.

Literature

1. Guzenkov G. A simple PAL/NTSC encoder for the "Electronics GIS-02T" generator. - Radio, 2005, No. 3, p. 11, 12.
2. Sarnin Yu., Sukhov Yu. LF generator. Sat: "To help the radio amateur", vol. 87, p. 34-41. - M.: DOSAAF, 1984.
3. Ivanov B.S. To help the radio circle. - M.: Radio and communication, 1987, MRB, vol. 1107, p. 21-25.
4. Borisov V. G. Block receiver for a beginner radio amateur. - M.: Radio and communication, 1987, p. 13, 14.
5. Polyakov V. Theory: a little about everything. 5.5. Amplifier with rigid temperature stabilization. - Radio, 2000, No. 1, p. 53, 54.

Author: G. Guzenkov

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