Homemade simple video signal RF modulator ----- RF MODULATOR

Keywords: video signal radio frequency modulator production, video signal radio frequency circuit, LA4112 power amplifier circuit diagram Homemade simple video signal RF modulator Recently due to the video signal RF modulator in the recorder, it is difficult to buy again. Causes that cannot watch video programs; for this purpose, a simple video signal RF modulator is made, and the use is good. The modulator is simple, making stool, no special requirements for components, and is very suitable for amateurous people. RF tuner circuit 1 shown in FIG. The emitter follower is composed of R3, C2, R1, R2, R4, and BG1. The video signal is moderately enlarged. C1 is a coupling capacitor, R5, L2, L3, L4, C4, C6, R6, and the like constitute a π-type low pass filter, BG2, L1, C7, etc., form an image carrier oscillation circuit, and its frequency is determined according to the selected television reception channel. of. This machine selects the first channel of the VHF band. C1, C9 is a resonant capacitor, and the C9 capacity is small, and the 2-3 cm long single plastic insulating line is used, and the coupling degree of the signal can be changed by adjusting its strand. C20 is a high-frequency filter capacitor, and L1 is an oscillation coil, D1 is an isolation diode for increasing the stability of the oscillation frequency. After the video signal input is filtered with the π-type low pass filter, mixed with the carrier signal, and then sent to the TV antenna jack via capacitor C5 and 75Ω feeder. The sound signal of this unit does not perform high frequency adjustment, but directly audio amplification. Use a speaker pronounce. The circuit is shown in Figure 2. Audio enlargement adopts integrated block La4112. Video and audio signals are made jack VCR video and audio output from. In this unit, the transistor BG2 can be used in 3DG56. BG1 is selected 3DG6, beta should be greater than 80. D1 has a better performance 2CK9. The speaker uses magnets. The L1 is removed from the lacquered line of 0.51 mm with a wire diameter, the coil inner diameter of 5 cm, L2, and L3 is removed from the lacquered line of 0.51 mm, and the inner diameter is 5 cm. After the decoration is complete, after the careful review, the signal output cable can be drawn to the TV antenna jack, and the TV wave band is adjusted in the VHF No. 1. Turn on the TV and modulator, the video recorder's power, the well brings the video signal and the audio signal output from the recorder to the input jack of the modulator, and the image is adjusted by adjusting the TV. When using, the volume on the TV should be placed at the lowest position. If there is no image signal when debugging, this may be that the BG2 does not start. If the image signal is very weak, it should first check that the BG1 emitter voltage is greater than 2V, and then makes other inspections; if the image is made of S-shaped distortion, it may be that the R7 resistance is too large. The sound part is not really true, and the sound is loud.