Color TV Compound Wireless Transmitter, Audio Transmitter
Keywords: television audio transmitter, wireless transmitter
Some people watched TV to see the sound, in order to avoid the interference to avoid the night to watch TV shows, they can add a sound-transmit circuit without changing the circuit, and then receive wireless FM headphones. The devices described herein use the FM emission mode.
The principle of circuit is shown in Figure 1. Where BG1 simultaneously serves as high frequency oscillation and audio modulation. C6 is a high frequency oscillation feedback element. The audio signal passes through C1 to the BG1 base, the voltage varies between the collector and the base, and the extremely small junction capacitance causes a large frequency display, thereby completing the frequency modulation. The modulation signal is output from the BG1 collector electrode, and the high frequency transformer B is coupled to BG2 as high frequency power amplification, and then transmitted to the indoor space by the antenna. The sound signal is controlled by the switch K, and when the switch k is set to "1", the device transmits a television audio signal. At this point, if you receive the 88 ~ 108 MHz FM radio, you can listen to the headset. At the same time, the television intercompanic power amplifier cuts off the frequency output signal and stops the play. When the "2" file is set, the transmit circuit disconnects the power, and the verifier output signal stops input, and the televisions are resumed to return to normal sound output. Component selection: BG1, BG2 Select or use 9018 high-frequency small power triode in the 3DG series, the FT should be greater than 300MHz, the β value should be greater than 40 and 50, and the saturated pressure drop is small; C3, C6 and C9 should use high frequency porcelain Dielectric capacitor; R1 ~ R8 should be selected from 1 / 8W metal film resistance; antenna is 600mm or so, the one end is connected to C9, and the appropriate increase of the antenna length can increase the emission distance accordingly; B use NX-40 core (M4 ×) 0.7 × 8) and a magnetic cover (φ9.5 × 7), the primary use φ0.17mm high-strength paint wiring wrap around 4, the secondary is in the same direction to 1 ~ 1.5; L1 is φ0.35mm 包, wound into φ4mm Empty core coil, a total of 12; C1 uses a metallized paper content. Assembly debugging: The component of the device is mounted on a small print plate, and the recommended printed board wiring and component are arranged as shown in FIG. The device debugging, no special instrument is required. Put K first "2" file, make the TV set up normal sound, then set the "1" file, first pick one 47kΩ potentiometer in the R1, and pull B near the FM radio rod antenna (5 cm) The radio volume is opened to the maximum, adjust the potentiometer until the radio speaker is the maximum sound of the radius (the IC of the BG1 is about 1.2mA), and the potentiometer is removed, and the corresponding resistance is replaced as R1. Next, the R4 is adjusted at 3m from the FM radio, which also makes the radio have a maximum sound of the sound (the IC of BG2 is 7 ~ 9mA). If the sound is too sound, you can adjust R4, while the small radio volume is tone. At this point, the distance of the radio can be disconnected. When the distance is 20m (the low-grade radio should be less than 10m), the radio noise should be the smallest, and the distortion is also minimal. In order to adapt to the large room, watch the requirements, the emission distance can be adjusted by one of the following methods. (1) Try L1, pull the coil (increased emission distance) or shorten (shortened emission distance), so that the signal of the radio is the clearest, the volume is the largest. (2) Elevation of the supply voltage emission distance increases, and the emitting distance is reduced. Adjusting R2 can change the frequency response. Adjusting B The core can change the operating frequency to avoid interference of FM broadcast. Circuit connection and switching: The tie rod antenna can be fixed outside the casing, first diamond a small hole in a proper position behind the housing. The transmitting device should be added to the metal box shield and are well grounded to reduce interference to other users. The casing can be used in place in the machine.
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