Simple KB signal generator. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Simple KB signal generator. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Civil radio communications

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Modern components make it possible in amateur conditions to manufacture a simple, but high-quality signal generator for setting up KB range equipment. A description of such a device was published by the German shortwave Hans Nussbaum (DJ1UGA) in the magazine "Funk" (Praeziser HF-Generator 1,6 - 30 MHz. - Funk, 2001, No. 11, S. 28-31). The diagram of this signal generator is shown in the figure. It covers the frequency band 1,6...30 MHz in two subbands (1,6...7 MHz and 7...30 MHz). The maximum output voltage is up to 3 V (peak value) at a load of 50 ohms and up to 6 V with a high-resistance load. The unevenness of the output signal level does not exceed 2 dB in the entire operating frequency band. The level of harmonic components in the output signal is not worse than -40 dB. phase noise at a 25 kHz offset does not exceed -80 dB (relative to the output signal level). The signal generator consumes no more than 60 mA at a supply voltage of 12 V.

Simple KB signal generator

The generator itself is assembled on a field-effect transistor VT1 according to a scheme that provides small changes in the level of the generator output signal when it is tuned in frequency over a wide range. This made it possible to cover the entire KB range using only two subbands (selected by the SA1 switch), and thus significantly simplify the device. However, this solution requires the use of a good vernier device for the built-in variable capacitor C1, without which it will be difficult to set the operating frequency. Moreover, to facilitate the setting of the operating frequency at the high-frequency ends of the subbands, it is advisable to introduce a single variable capacitor with a maximum capacitance of 15 ... 30 pF into the device, connecting it in parallel with one of the sections of the capacitor C1. As for the reading of the operating frequency, this problem is solved by using an external digital frequency meter, the manufacture of which today does not cause problems for radio amateurs. The generator supply voltage (8 V) is stabilized by the integral stabilizer DA1.

A high-frequency voltage with a level of approximately 100 mV is removed from the gate of the field-effect transistor VT1 and, through a decoupling resistor R4, is fed to the output signal level regulator - a variable resistor R5. Capacitor C5 compensates for the blockage at high frequencies of the frequency response of the divider formed by resistors R4 and R5 + R6.

From the engine of the resistor R5, the RF voltage is supplied to the broadband integrated amplifier DA2. The operating mode of this amplifier is set by a tuned resistor R9. To do this, the engine of the variable resistor R5 is transferred to the upper position according to the scheme and, by adjusting the resistor R9, the output signal is not limited. When carrying out this operation, the device output ("Output 2") must be loaded with a 50 Ohm resistor.

The output voltage level is controlled by an RF voltmeter (R15, VD2, C12, RA1). The microammeter PA1 has a total deflection current of 100 µA. The frequency meter is connected to "Output 1".

Structurally, the device is assembled on a board made of foil fiberglass with mounting "on patches" with a diameter of 5 mm. BAR28 diodes are high frequency Schottky diodes. The MSA0886 chip is designed for surface mounting. Its direct counterpart in a larger "traditional" package is the MSA0885. Similar broadband amplifiers are produced by many foreign companies.

Author: Hans Nussbaum (DJ1UGA)

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