Quartz calibrator. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Measuring technology

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To adjust, adjust and calibrate the scales of radio receivers and amateur radio measuring generators and to verify them during long-term operation, a signal source of a higher accuracy and stability class is needed. The proposed version of the quartz calibrator provides at the output a grid of modulated harmonics of the fundamental frequency of the used quartz resonator. So, when using quartz with a nominal frequency of 100 kHz, the 16th harmonic is easily detected on a receiver with a KB range of 19 - 160 m. Such a device can be useful not only for radio amateurs, but in some cases in service departments, at enterprises.

The design of the calibrator is simple in terms of circuitry, does not contain scarce radio elements, has small dimensions and is easy to adjust. In a copy of the test device made by the author, it was shown that without additional adjustments, quartz resonators are confidently excited with a frequency of up to 15 MHz, which makes it possible to expand the grid of calibration marks up to the frequencies of the television ranges of meter waves.

The scheme of the device is shown in fig. 1. On the transistor VT1, a master oscillator is made according to the capacitive three-point scheme. The generation frequency is determined by a quartz resonator connected to the XS1 sockets. To facilitate the excitation of the resonator at frequencies below 2,5 MHz, the contacts of the switch SB1 should be closed. The output to the generation mode depends on the base current, which can be selected with a variable resistor R1. The generated oscillations are non-sinusoidal.

Fig. 1. Schematic diagram

Rice. 2. PCB

On the transistor VT2, an emitter follower is made, and on VT3, an amplifier with a two-way signal limiter. From the latter, the signal is fed through the capacitor C7 to the output connector XS2 and to one of the diagonals of the bridge modulator on the diodes VD1 - VD4 and the transistor VT4.

An audio frequency signal generated by an oscillator based on a VT5 transistor is fed into the other diagonal. A resonant oscillatory circuit is included in the collector circuit of the generator with self-excitation, consisting of winding 3-4 of the transformer T1 and capacitor C9 and determining the generation frequency within 1,5 ... 2 kHz. Positive feedback from the windings 5-6 of the transformer is fed into the emitter circuit of the transistor.

The board of the quartz calibrator is made using double-sided foil fiberglass with a thickness of 1,5 ... 2 mm. The installation is one-sided, but the foil on the other side of the board should not be removed, since it acts as a screen. In the author's version, this part of the board also acts as a front panel. Then it is necessary to provide for the structural and graphic design of controls and connectors on it.

It is advisable to check the radio elements before installing them on the board, especially for transistors. They should be selected with a base current transfer coefficient of at least 30. In addition to those recommended in the design of a quartz calibrator, instead of P416A, transistors of the P308, GT308, KT361 groups can be used, and instead of P16 - MP21, MP39, MP41 with an allowable voltage between the collector and emitter of at least 25 IN.

When making the transformer yourself, you should take the Sh4x5 magnetic circuit and wind the windings with a PEL 0,07 wire: 1-2 - 500, 3-4 - 2500 and 5-6 - 200 turns. It can be performed on the basis of a ready-made transformer from transistor small-sized receivers, for example, "Speedola", "VEF-12", "Alpinist", "Sokol" and others. It will be enough to supplement the transformer of these receivers with a winding of 5-6, proportional in the number of turns (see self-made data) to its collector winding. It will be enough to supplement the transformer of these receivers with a 5-6 winding proportional to the number of turns (see self-made data) to the board should be fixed with a metal strip (clamp) with two screws.

If the installation was carried out without errors and the radio elements were checked before their installation, the device starts working immediately. When adjusting the device, you should first check the current consumption, in operating mode it can reach 30 ... 35 mA.

To check the generation, you must have a set of quartz resonators: 0,1, 1 and 10 MHz. As an indicator of fluctuations, it is desirable to have an oscilloscope or an alternating current millivoltmeter with operating frequencies of at least 10 MHz. Connect the quartz resonator to the sockets, set the variable resistors R1 and R7 to the positions of minimum resistance between the engine and the common power bus, and R14 to the middle position. By rotating the resistor R1 on an oscilloscope or an AC voltmeter connected to the output connector XS2, generation is achieved. Then, with the resistor R7, the required oscillation amplitude and the symmetry of the restrictions are set (it is possible to determine only on an oscilloscope).

In the absence of measuring equipment, the control of oscillation generation and the presence of harmonics can be carried out with a conventional broadcasting receiver having CB and HF bands. In this case, a piece of any wire 1 m long should be connected to the output socket of the quartz calibrator. may be hazardous to the input device semiconductors).

Author: S. Biryukov, Moscow; Publication: cxem.net

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