The LM389 is a low-voltage audio amplifier integrated circuit manufactured by NS Corporation of the United States. It is an 18-pin DIP dual in-line package containing a power amplifier similar to the LM386 and three independent NPN transistors. Some limit operating parameters of each transistor are as follows: Bvco=12V, Bvcbo=15, Icm=25mA, Pcm=150mW, and the two-way radio intercom circuit designed with LM389 is shown in the drawing. The audio power amplifier is used for transmitting and receiving amplification. Among the three transistors, VT1 is used as carrier crystal oscillator, VT2 is used as carrier amplifier, and VT3 is used as super-regeneration receiving detector. The half-duplex communication mode is adopted, but there are two channels: the transmission frequency of the transmission is 28 MHz; the transmission frequency of the transmission is 29 MHz. Therefore, it is easy to change to a full-duplex communication circuit that can be heard and spoken at the same time. The walkie-talkie adopts amateur frequency and does not affect other communication equipment. It can be used in teaching, tourism, construction sites, field operations, and inconvenient mobile phone calls. 1 circuit principle Quartz crystal XT, VT1, etc. constitute a high stability carrier oscillator. The oscillating signal is coupled to L2 by L1. Carrier power amplification is performed by VT2. C1, C2, L1 and C5, C6, L3 form two parallel frequency selection loops. When their resonant frequency is consistent with the XT natural oscillation frequency, the maximum transmission power can be obtained, and the general call distance can reach 2.5km~3km. When S1 sets the transmitting position (the position shown in the drawing), the audio signal picked up by the microphone BM is amplified by the LM389, and is applied to the modulation transformer T1. The operating voltage of the carrier power amplifier tube VT2 is controlled by the level of the audio signal. The amplitude modulation (amplitude modulation) of the oscillating signal is realized, and then sent to the antenna ANT via C8 and L4 to transmit to the space. R1, R2 determine, VT1 operating point. VT3 and other self-extinguishing super-regeneration receiving detection circuit is determined by the parallel resonant circuit composed of C10, c11 and L5 according to the receiving frequency (ie, the transmitting frequency of the opposite machine). R7 is used to set the VT3 DC operating point, and together with C13 to determine the self-extinguishing frequency, which should be higher than the audio and lower than the carrier oscillation frequency, usually hundreds of kilohertz. The sensitivity of the super-regenerative detection is very high, and the amplification rate of the weak signal can reach several hundred thousand times. It is similar to the standard superheterodyne receiver with one-stage independent local oscillator, one-stage mixing, and two-stage intermediate release, but its The selectivity and signal to noise ratio are slightly worse. R6 is the detection load resistance, and the demodulated (de-carrier) audio signal is filtered by R8, c14, and c15, and then amplified by the LM389 to drive the speaker BL to sound. When the BL impedance is 8 Ω, an undistorted output power of 450 mV is obtained. 2. Component selection and production The microphone BM selects domestic electret microphones such as CR2-9, 15, and 16. XT selects JA12 crystal oscillator with frequency of 28MHz and 29MHz, ANT selects 1.5m rod antenna. T1 uses a small input transformer of ordinary transistor radio. There are 5 wire ends. One side of the two wire heads is the primary one, and the other three wire heads are the secondary ones. Only the adjacent two are used, the other one is empty, and the cross section is 5mm & TImes. 5mm E19 silicon steel sheet core self-made, primary Φ0.06mm enameled wire wrapped around 1500 laps, secondary with the same number line around 500 laps. Homemade L1～L6: L1 and L5 use Φ0.4mm enameled wire to wrap 14 turns on Φ8mm wire frame; L2 uses single strand plastic wire to wrap 2 times on L1; L3 uses Φ1mm enameled wire to circulate 10 times on Φ12mm coil frame. Center tap . It can be wound in two lines, and then one is not used: L4 is an antenna plus inductance coil, which can shorten the length of the antenna after use. It can be wound 30 times on the Φ15mm coil frame with Φ0.71mm enameled wire. L6 is a high frequency choke, optional 216mH ~ 36mH finished inductor. S1 selects 3&TImes; 2 compression spring type self-locking switch, the other component parameters are marked with the drawing, no special requirements. 3 debugging methods and steps (1) Use the 50kΩ potentiometer to temporarily replace the R1 of the machine. When the potentiometer is adjusted from large to small, the VT1 collector current gradually rises to a certain value, and suddenly falls. At this time, the XT current is turned off and then rises. Connect XT. The current drops again, indicating that the circuit has started to oscillate. Then slightly adjust the potentiometer slightly. Make the current drop by 1mA~2mA again, avoid the strongest point of oscillation (the stability is poor when the oscillation is strongest), and then replace the potentiometer with the same value fixed resistor. The same method adjusts the B machine to make its carrier oscillator work stably. (2) Use the 1MΩ potentiometer to temporarily replace the R7 of the machine. Adjust the potentiometer from large to small to make the super-regeneration noise in the speaker BL of the machine the loudest. There is no whistling, bursting and other noises (can be eliminated with the adjustment of C15) . Open the machine to make it in the transmitting state, adjust the length of C1, C2, C5, C6 and L1, L3 or the spacing of the machine. Then adjust the C10, C11, L5 and C12 of the machine to make the super-regeneration in the BL of the machine. The noise completely disappeared. It became silent. When speaking to the BM of the machine BM, the BL of the machine should emit a loud and clear sound without distortion or blockage, indicating that the receiving frequency of the machine is basically the same as the transmitting frequency of the machine. Then gradually pull away the distance between the two machines (the distance between each distance is slightly super-regenerated noise of the machine BL), and repeat the above adjustment steps until the distance between the two machines is the farthest. Then replace the same value with the fixed resistance. Potentiometer. Use the same method to adjust the B machine so that the transmission frequency of the A machine is the same as the receiving frequency of the B machine, and the call distance is the farthest. Digital currency transactions allow users to convert existing digital currencies into other digital currencies. The entire transaction does not involve any legal tender. Because of the relatively loose regulation, the mainstream digital currency trading platform also opened this function.Digital Asset Exchange (DAE) is a platform for matching transactions between digital currencies, digital currencies and legal currencies. 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