KB converter. Scheme, description

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

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Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur

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The scheme of this converter was found in one old book (N. N. Putyatin. To help a novice radio amateur. - M .: MRB, 1975, p. 103). It connects to any radio receiver that has a medium wave (MW) range and allows you to listen to shortwave (HF) radio stations. The converter was assembled by me and showed excellent results, taking fairly distant stations. Therefore, it seems to me that his description should be of interest to the readers of the Radio magazine.

The converter, the schematic diagram of which is shown in fig. 1, assembled on only one transistor VT1. This transistor performs the functions of both a mixer and a local oscillator, thus converting the signal frequency from HF to MW. The range of received frequencies is 5...12 MHz (wavelengths from 60 to 25 m). The broadcasting bands 60, 49, 42, 31 and 25 m fall into this interval.

KB converter

The radio station signal received by the antenna, through the coupling capacitor C2, enters the oscillatory circuit L1C1.1C3. Highlighted by the circuit, the signal through the coupling coil L2 and the decoupling capacitor C4 is fed to the base of the transistor. At the same time, a local oscillator signal enters the emitter circuit from the tap of the L3C7C8C1.2 heterodyne coil. To excite the oscillations of the local oscillator, the feedback coil L4 is used, which is included in the collector circuit of the transistor. The local oscillator frequency should be approximately 1,5 MHz higher than the signal frequency.

An intermediate frequency signal of 1500 kHz is selected in the collector circuit by the L5C6 circuit, tuned to this frequency, and is fed through the capacitor C10 to the receiver's antenna jack. The receiver with which the converter works is tuned to a frequency of 1500 kHz - this is the upper part of the MW range. You should make sure that there are no powerful broadcasting stations operating on this frequency that can cause interference. The converter is tuned to the frequencies of KB radio stations by a block of variable capacitors (KPE) C1.1 and C1.2. More precise tuning within small frequency limits can also be done with the tuning knob of the receiver itself.

A few words about the details of the converter. Transistor VT1 is applicable to any of the series P416, P403. It is also permissible to use silicon transistors KT361, KT315 (in the latter case, the polarity of the power source changes). Capacitor block - KPE-2V, KPP-2 or another suitable one. Trimmer and constant capacitors, as well as resistors can be of any type, only the size of the converter printed circuit board will depend on them.

The sketch of the printed circuit board is shown in fig. 2. It is not necessary to drill holes, the leads of the parts can be soldered directly to the pads from the foil side. Before manufacturing the board, it is recommended to clarify its drawing in accordance with the dimensions of the available parts.

KB converter

All coils are wound on frames with a diameter of 8 mm with trimmers of the SCR-1 type made of carbonyl iron (frames from the FPC of the Rubin TV). In total, three frames are needed. Coil L1 contains 24 turns, coil L2 is wound over L1 at its beginning and contains 2 - 3 turns. The local oscillator coil L3 contains 21 turns with a tap from the second turn, counting from the beginning. Wire - PEV0.2-0,4. Coil L4 is wound over coil L3 at its beginning. It contains 7-10 turns of PEV wire 0,1-0,15. For an intermediate hour-gota of 1,5 MHz, the L5 coil must contain 50 turns of PEV 0,2 wire.

Setting up the converter consists in setting the operating mode of the transistor and adjusting the range limits within 25 ... 60 m. The antenna is a wire about 1 m long. The converter is powered from its own battery, as shown in fig. 1, or from the receiver's battery.

Author: A. Gavrilov, Usolye-Sibirskoye, Irkutsk region.

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