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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Training complex for a beginner radio sportsman. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur Initially, the training complex was developed as a visual aid to explain the existing principles of information transfer. But it turned out that it is quite suitable for conducting practical exercises on mastering the skills of operator work on the key, studying Morse code, receiving and transmitting telegraph and voice messages over a wire line, over radio and a laser beam. The block diagram of the complex is shown in fig. 1. Its main unit 1 consists of a transmitter, a 3H generator and a power supply. The operation of the generator is controlled by the Morse key, you can listen to the signals of the generator through headphones directly connected to the output of the generator or installed at the end of a two-wire line.
If the message is transmitted through a transmitter, either an FM receiver (2) or a super-regenerative one (3) is included in the work. When using optical communication, block 4 applies, and for receiving messages, block 5. The transmitter can be tuned to 27,12 MHz. Its maximum power, when modulated by a carrier with an audio frequency signal, reaches 180 ... .200 mW, which makes it possible to maintain communication at a distance of up to a kilometer. But before you assemble the transmitter and operate it, you must obtain the appropriate permission from the State Telecommunications Inspectorate. The transmitter (Fig. 2) consists of a two-stage AF amplifier, made on transistors VT1, VT2, and a master push-pull oscillator on transistors VT3, VT4. At the input of the amplifier through the SA1 switch, you can apply a signal either from a microphone or from an AF generator. Through the coupling capacitor C1, the signal is fed to the base of the transistor VT1 of the first stage of the amplifier. From the load resistor R2, the amplified signal is fed through the capacitor C2 to the base of the transistor VT2 of the second stage. From its load resistor R4, the signal enters through the capacitor C3 and limiting resistors R7, R8 to the bases of transistors VT3, VT4 of the master oscillator, performing amplitude modulation of its high-frequency signal.
The supply voltage to the collectors of the generator transistors is supplied through the high-frequency inductor L1 and the coil L2. The inductor prevents the high-frequency component from entering the power circuit of the simulator. The L4 coil is used to connect the master oscillator circuit with the antenna circuit, and the L3 coil with a trimmer is used to tune the antenna into resonance with the frequency of the master oscillator. A piece of insulated copper wire about a meter long was used as an antenna. The order of manufacture of the transmitter is as follows. First, pick up all the radio components and check their performance. Transistors VT3, VT4 must be with the closest parameters and current transfer ratio of at least 70. Then you need to make coils. They will need polystyrene frames with a diameter of 8 mm. On fig. 3 shows the dimensions of the frames of both the transmitter and receiver coils. Alternatively, segments of round ballpoint pens can be used for reels. Trimmers made of carbonyl iron - SCR Inside the frame of the coil, the trimmer is fastened with a threaded thread or a thin piece of elastic. After tuning, the trimmer can be fixed with a drop of melted wax or paraffin. In the same way, it is permissible to mount coils on a printed circuit board.
The coils are wound in one layer turn to turn with PEL 0,5 wire. Coils L3 of the transmitter and L1 of the receiver each contain 10 turns, L2 - 4 + 4 turns, L4 - 4 turns placed between the halves of the L2 coil. Inductors can be ready-made, with an inductance of 40 μH, but it is not difficult to make them yourself. To do this, a resistor of any type with a power of at least 0,5 W with a resistance of approximately 1 MΩ must be wound in bulk with 200 turns of PEV or PEL wire with a diameter of 0,1 mm. When using a wire of a larger diameter, it is recommended to install (glue) cardboard cheeks along the edges of the resistor. Now you can start manufacturing a printed circuit board (Fig. 4) from one-sided foil fiberglass. Insulating tracks on it are cut with a special cutter, made, for example, from a piece of a hacksaw blade.
To save space, resistors on the board can be installed vertically. It should be noted that the parts marked with an asterisk in the diagram (they will have to be selected) should be temporarily mounted on the board from the side of the tracks, without shortening their leads. Capacitor C3 is installed on the board after setting up the 3H amplifier and generator. Turning to the installation of the high-frequency part of the transmitter, make all leads and connections as short as possible. Shorten the transistor leads to 1 cm. Place the inductor and coils perpendicular to each other. Separate the details of the master oscillator from the rest of the installation with a screen made of thin tin or copper, soldering it to the positive track of the board with a tinned copper wire with a diameter of 0,6 ... 0,8 mm. The establishment of the transmitter begins with a 3-hour amplifier. By selecting the resistor R3 set the voltage at the collector of the transistor VT2 equal to half the supply voltage. Then, by supplying a sinusoidal signal with a frequency of 10OO Hz and an amplitude of 50 mV from an industrial AF generator to the input of the amplifier, the waveform at the collector of the transistor VT2 is observed using an oscilloscope. The selection of the resistor R1 eliminates signal distortion. Instead of an oscilloscope, high-resistance headphones with a resistance of about 4 kOhm are connected through a capacitor with a capacity of about 1 μF to the output of the amplifier (in parallel with resistor R4) - two series-connected capsules of TON-2 type phones - and by selecting resistors R1, R3 achieve undistorted sound. Then they move on to the generator. A milliammeter is turned on in the gap of the left inductor L1 according to the output circuit and a current of 5 ... 9 mA is set by selecting the resistor R60 (and, if necessary, R70). By more accurate selection of resistor R5, the required bias voltage is achieved at the bases of transistors VT3, VT4 to obtain the generation mode. If necessary, by selecting capacitor C7, stable generation is achieved. Further, by selecting resistors R7, R8, they achieve the maximum and the same signal amplitude in both arms of the generator. The control is carried out using an oscilloscope connected alternately to the outputs of the emitter and collector of the generator transistors. After that, you can solder the capacitor C3, and apply a signal from the 3H generator to the input of the amplifier. The generator is tuned to the allowed range of 27,12 MHz using a calibrated reference receiver or wavemeter. By bringing the transmitter closer to the receiver and moving the rotor of the trimmer capacitor C8, they achieve sound in the receiver. By adjusting the position of the L3 coil trimmer, the antenna circuit is tuned to resonance with the frequency of the generator circuit. In this case, the volume of the sound of the receiver should be maximum. The audio frequency generator (Fig. 5) is made on two transistors. Moreover, the generator itself is assembled according to the capacitive three-point scheme on the transistor VT1, and a repeater is made on VT2. Capacitors C1, C2 provide the necessary conditions for the occurrence of feedback. The frequency of the generated oscillations is determined by their capacitance and the inductance of the coil L1. In this design, a coil was used, wound on an armored core of the SB brand, version a (for example, SB-12a) with a PEL 0,1 wire. The number of turns is 500.
By adjusting the position of the coil trimmer and the slider of the resistor R1 (it should be approximately in the middle position with the appropriate selection of the resistor R2), the best shape of the sinusoidal signal on the collector of the transistor VT1 is achieved. You can do without an oscilloscope if you connect BF1 headphones (TON-2 type) instead of a coil and achieve undistorted sound. In this version, the phones will become an indicator of the control of the generator. With the help of resistor R1, it will be possible to change the frequency of the audio signal from 500 to 5000 Hz, and with resistor R6 to regulate the output signal coming to the line or to the input of the transmitter, in the range from 0 to 2 V. As for the telegraph key, it is included in the break in the power circuit . In the initial state, the key contacts are open, so the generator does not work. A short press on the key corresponds to a dot, a long press to a dash of the telegraph alphabet. When the generator is needed to check the operation of the low-frequency cascades of the simulator, the key contacts must be closed. The use of a repeater in the generator allows you to connect to it a two-wire line with a length of several tens and even hundreds of meters. The establishment of the generator is reduced to setting the operating mode of the transistor VT1 in a strictly linear mode. To do this, turn off the feedback by unsoldering the wire that goes from the point of connection of the capacitors C1, C2 to the base of the transistor VT2, and select the resistor R2 of such resistance that with the middle position of the slider of the resistor R1, the voltage at the emitter of the transistor VT1 was 3 ... 4 V. Further, from the AF generator, a signal with an amplitude of 1 V and a frequency of 1 kHz is fed to the base of the transistor VT5 through an isolation capacitor with a capacity of 0,05 ... 1 μF. The output signal at the collector of the transistor observed with an oscilloscope should be amplified by 10 ... 20 times. If this does not happen, you should choose a transistor with a large current transfer coefficient. Power supply (Fig. 6) - stabilized, with adjustable output voltage. The network transformer must output an alternating voltage on the secondary winding, approximately 1,5 ... 2 times greater than the stabilization voltage at a load current of up to 0,5 A.
The block parts are placed on a printed circuit board (Fig. 7) made of one-sided foil fiberglass. Transistor VT2 is mounted on a radiator from a metal corner, isolated from the board.
When establishing a power supply by selecting a resistor R1, a current of 15 ... 20 mA is set in the zener diode circuit. After that, the trimming resistor R2 achieves the output voltage indicated on the circuit at terminals X2, X3 at a load current of about 100 mA. The transmitter, generator and power supply are housed in a housing from a three-program subscriber loudspeaker (Fig. 8).
The super-regenerative receiver (Fig. 9) of the simulator provides a sufficiently high sensitivity - 5...15 µV. With this sensitivity, the communication range reaches 1 km.
A super-regenerative detector is assembled on transistor VT1, and a 2-hour amplifier is assembled on VT3 and VT3. The high-frequency signal received by the WA1 antenna is fed through the capacitor C3 to the input circuit L1C5. Further, it is amplified and detected by a super-regenerative cascade on the transistor VT1, the load of which is the resistor R3. The low-frequency signal selected on the R5C8 filter is fed through the capacitor C7 to a two-stage 3H amplifier, made on transistors VT2, VT3. The load of the output stage of the amplifier is high-resistance headphones BF1 (for example, TON-2). Most of the receiver parts are mounted on a printed circuit board (Fig. 10) made of one-sided foil fiberglass.
When connected to a power source receiver, a hissing noise will be heard in the headphones if the super-regenerator is working normally. In the absence of noise or its low volume, the operation mode of the transistor VT1 is changed by selecting the resistor R1. Next, the transmitter is turned on by applying a continuous signal from the 3-hour generator to its input. By selecting capacitor C6, changing the position of the rotor of capacitor C5 and the coil trimmer L1, they are tuned to the frequency of the transmitter. A good sound of the received signal is achieved by selecting parts C4, R3. Sometimes this result can be achieved by selecting the capacitor C1. For the time of adjustment, instead of a constant resistor R1, it is advisable to connect a variable with a resistance of 30-51 kOhm and use it to achieve the maximum signal volume in phones, then measure the resulting resistance and solder a constant resistor of such resistance. The operation mode of transistors VT2, VT3 of the 3H amplifier is set according to a similar method described for the same transmitter amplifier. The laser beam modulator (Fig. 11) is a single-stage power amplifier based on a VT1 transistor, the load of which is a laser pointer. The signal can be fed to the input of the modulator either from the 3H generator when the operator works with a key, or from the 3H amplifier when the operator works with a microphone. For this purpose, you can use any industrial 3-hour amplifier with a power of at least 1 W and an output signal amplitude of about 1 V.
The signal through the decoupling capacitor C1 is fed to the base of the transistor VT1. With a variable resistor R1, depending on the modification of the pointer used, and, consequently, its internal resistance, the operating mode of the transistor is set so that the voltage drop at the pointer terminals is 4 V. The optimal amplitude of the input signal of the modulator when working with the key is set by the variable resistor R6 generator 3H. And the required signal level when working from a microphone is set by the output level controls of the used 3H amplifier. The sound quality of the transmitted information is checked by ear using any 3-hour household amplifier with a microphone input with a sensitivity of 3 mV. To do this, a photosensitive element (photodiode or phototransistor) is connected to the microphone input of the amplifier. The resulting photodetector (block 5 in Fig. 1) is placed at a distance of about 5 m from the emitter (block 4). In the proposed development, the modulator emitter and the photodetector are mounted on photo stands (Fig. 12) from old photo enlargers, which makes it quite easy to adjust the optical alignment of the equipment.
By adjusting the vertical and horizontal position of the bracket with a fixed laser pointer on one of the tripod rods, and the position of the bracket with the photodetector on the other rod, their optical axes are matched. After that, by adjusting the variable resistors mentioned earlier, the loudest and most undistorted sound is achieved. During experiments on the transmission of information along a laser beam using a condenser from the same photographic enlarger, it was possible to increase the communication range several times. Author: A.Dronov, Moscow
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