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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Universal notification device. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Security devices and object signaling The notification device described in the article is a radio channel with one-way transmission of information. It can be used in various fields of activity. For example, as a radio security device for various objects. It can be installed in the room of a sleeping child or a sick person, at a regular telephone or at the doorbell of an apartment, and with a radio receiver it can be within a radius of 5 km. Since the transmitter has voice control, it will switch to transmit mode from the speaker's speech, noise or other sounds. The device can also be used as a radio microphone or as a paging system for the home. If the receiver is with a child walking in the yard, you can always call him using the call button or voice. This device can also be used in radio control of various objects. By supplementing the transmitter and receiver with an encoder and a command decoder, respectively, it is possible to significantly expand the scope of this device. Such devices have long been produced by many foreign firms, but in the domestic literature it is described for the first time. The device uses narrowband frequency modulation with a deviation of 2,5 kHz, a very sensitive receiver (with a sensitivity of 5 μV / m to the built-in loop antenna) and a radio transmitter with a power of not more than 10 mW. The device does not contain a scarce element base, it is very easy to set up and can be repeated even by novice radio amateurs. Consider the operation of the device. Schematic diagram of the radio receiver is shown in Fig.1. It is built according to the superheterodyne scheme with one frequency conversion.
The received signal is fed to the loop antenna WA1. It is tuned to resonance by the capacitor C50 at a frequency of 144 MHz. Loop antennas are preferable for portable radios, because. they are not affected by surrounding objects, and when the length of the perimeter of the frame is less than the wavelength, its directional properties have almost no effect on the operation of the receiver. From the antenna, the signal is fed to a two-stage high-frequency amplifier built on transistors VT1 and VT2 of the KT399A type, operating in the barrier mode. Circuits L1, C5; L2, C4 and L3, C10 are also tuned to 144 MHz. A local oscillator voltage with a frequency of 135 MHz is also supplied here from the tap of the coil L5 through the capacitor C15. The mixer transistor also operates in barrier mode. The load of the mixer is the circuit L4, C8, tuned to a frequency of 9 MHz. She is intermediate. From the tap of the L4 coil, the IF signal is fed to an intermediate frequency amplifier based on a VT4 transistor of the KT368A type. It also works in barrier mode. The load of the IF is the FSS on the elements L6, C18, C51, L8, C22, C52, L9, C23. From the L9 coil, the IF signal is fed to the DA1 chip of the K174XA6 type for further amplification and detection. The reference circuit of the frequency detector of the DA1 L12, C3З chip is tuned to a frequency of 9 MHz. Switch SA1 is used to turn off the noise reduction system. From pin 7 of the DA1 microcircuit, the low-frequency signal is fed to a low-frequency amplifier made on transistors VT8 ... VT12. The ULF output stage operates in mode B. Its total current consumption in silent mode with the noise suppressor turned on does not exceed 1 mA. Resistor R26 serves as a volume control. The receiver local oscillator is built on transistors VT5 and VT6. A crystal oscillator is built on the VT6 transistor. The quartz resonator ZQ1 is excited at the third mechanical harmonic, i.e. at a frequency of 45 MHz. A frequency tripler is built on the VT5 transistor, its load is the L5 circuit, SI, tuned to a frequency of 135 MHz. Coil L10 serves to shift within a small range of the frequency of the oscillator. An economizer is built on element D1, which turns on the receiver for two seconds every ten seconds. This saves the energy of the power supply. The economizer can be switched off with switch SA2. The receiver is powered by a 6V power supply. Schematic diagram of the radio transmitter is shown in Fig.2. The transmitter master oscillator is built on a VT10 transistor of the KT368A type. It uses quartz frequency stabilization. The quartz resonator ZQ1 at a frequency of 16 MHz is excited at the third mechanical harmonic, i.e. at a frequency close to 48 MHz. The load of the crystal oscillator is the circuit on the elements L2, C24, C25, tuned to a frequency of 48 MHz. A frequency tripler is built on a VT6 transistor of the KT399A type. In the circuit L1, C22, C23, a frequency of 144 MHz is allocated and then fed to a line of amplifiers based on transistors VT7 ... VT9. The output matching filter is built on the elements L15 ... L17, C42 ... C45, it matches the output stage with the WA1 antenna. As the WA1 antenna, a telescopic antenna from pocket radios was used, shortened to 50 cm. The microphone amplifier and the low-frequency signal compressor are built on the DA1 chip, the VT1 transistor and the VD3 and VD4 diodes. The compression level can be set by selecting the value of the resistor R3. As a microphone, an M1 electret microphone of the MKE-3 type or any other, with the appropriate inclusion, was used. A low-pass filter with a cutoff frequency of 11 kHz is built on transistors VT12 and VT3. The output signal level, and hence the frequency deviation of the radio transmitter, can be set by resistor R22. On transistors VT2 ... VT5, a radio transmitter voice control system was built. Its turn-on delay is approximately 0,1 s, and its turn-off delay is 5 s. She has no special features. You can turn off the voice control system with the SA3 switch. An intermittent tone signal generator is built on the D1 element. It can be submitted using the SA2 button. She works for breaking. Various alarm sensors can be connected to connector X1. The transmitter is powered by a 12 V power supply, and when the voice control system is on, it consumes practically no energy. The device uses resistors of types MLT, S2-23, S2-33; capacitors - KM4, KM5, KG, KD, KLS, K10-7v, K10-17; transistors - KT315, KT316, KT368, KT325, KT355, KT399, etc., K174XA6 microcircuits, you can also K174UR1, K174URZ with their appropriate inclusion. The winding data of the receiver and transmitter coils are given in Tables 1 and 2, respectively. The receiver and transmitter are mounted on printed circuit boards made of double-sided foil fiberglass with a thickness of 1,5 mm, and the foil on the installation side of the elements is completely preserved and serves as a screen and a common conductor. It is removed by countersinking only around the terminals of the elements, Table 1. Receiver
not connected to a common wire. The receiver loop antenna has a size of 65x45 mm. It is made of copper wire with a diameter of 1,5 mm. It can also be made from a thin coaxial cable, closing the braid with the core on both sides. Capacitor C50 is included in the break of the frame. The best results can be obtained if the antenna is made in the form of three parallel conductors with a distance of 3 mm between them. Solder the conductors together on the plates of the capacitor C50. It is best to first make an insulating frame with a size of 65x45 mm and a width of 10 mm from polystyrene with three grooves at a distance of 3 mm from each other, and then lay a silver-plated wire with a diameter of 1 mm in them. Such an antenna will have a very high quality factor. Setting up the device should begin with a radio transmitter. After turning off the voice control system of the SA3 toggle switch, power is supplied by the SA1 toggle switch. In this case, the master oscillator on the transistor VT10 should start working. If it is not excited, then rotate the core of the coil L2 until it is excited. By connecting an RF voltmeter to the base of the transistor VT8, adjust the circuit L1, C22, C23 to the maximum output voltage. Next, a 50 ohm resistor is connected to the transmitter output and the output stage is set up. In this case, it is necessary to ensure that the power does not exceed 10 mW. defined as the power of out-of-band emissions by the State Telecommunications Inspectorate. The final adjustment of the transmitter stages is carried out on a real whip antenna. The control is carried out with a wavemeter or a selective voltmeter. Next, go to the setting of the low-frequency part of the transmitter. A sound generator is connected to the resistor R2 and a signal of the order of 5 mV and a frequency of 1 kHz is applied. In this case, the emitter of the transistor VT11 should have an undistorted signal when the input signal grows to a value of the order of 1,5V. Further, having connected the microphone, they pronounce a long "a" at the required distance from it, with the resistor R22 set the frequency deviation of 3 kHz. Turn on the voice control system of the SA3 switch and make sure that it works correctly. After pronouncing a long "a" in front of the microphone, the transmitter must be in transmit mode for at least 5 seconds. If necessary, select the value of the resistor R13.
Table 2. Transmitter
Pressing the SA2 button makes sure that the intermittent tone generator is working. Coil L12 serves for the final pairing of the receiver and transmitter. Now we move on to setting up the receiver. Turn off the economizer and the noise reduction system with switches SA3 and SA1, respectively. Turn on power. A low-frequency signal of 26 mV and a frequency of 50 kHz is applied to the resistor R1, and a clean, undistorted tone is achieved in the dynamic head B1. The slider of the resistor R26 must be in the maximum volume position. Next, pin 18 of the DA1 chip is supplied with an RF voltage with a frequency of 9 MHz, an amplitude of 100 μV and a deviation of 3 kHz. By rotating the cores of the coils L9 and L11, they achieve maximum volume in the dynamic head B1. Then the same voltage, but with a value of 10 μV, is applied to the base of the transistor VT3, and the circuits L4, C8 are tuned; L6, C18 and L8, C22 for maximum volume. In this case, non-linear distortions should be absent. The receiver local oscillator is tuned in the same way as the transmitter master oscillator, because their schemes are similar. Now a voltage is applied with a frequency of 144 MHz, a value of 10 μV with a deviation of 3 kHz to the base of the transistor VT1. By rotating the corresponding cores, the contours L1, C5 are adjusted; L2, C4 and L3, C10 V resonance. In this case, the input voltage is reduced to a value of 0,3 μV. Then, the receiver and transmitter are paired in frequency by rotating the cores of the coils - L1 of the receiver and L2 of the transmitter, and also adjust the loop antenna by rotating the rotor of the capacitor C50 to the maximum sensitivity of the receiver. It should be no worse than 5 μV / m with a signal-to-noise ratio of 20 dB. Next, the noise reduction system is turned on with the SA1 switch, and at maximum sensitivity, its clear operation is achieved by rotating the slider of the resistor R16. Next, switch SA2 turn on the economizer and check its operation. This completes the setup of the receiver and the entire system as a whole. The described system has been repeated many times and has proven itself well. For the purchase of printed circuit board drawings, please contact the author, enclosing an envelope with a return address. Literature 1. V. Stasenko. barrier mode of operation of the transistor. - Radio amateur, 1996, No. 1. Author: V. Stasenko (RA3QEJ), Voronezh region, Rossosh; Publication: N. Bolshakov, rf.atnn.ru
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