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Wireless video system with AM stereo channel conversion circuit

Published on Dec 20 2010 // Wireless Transmitter Circuits

Wireless video system with AM stereo channel conversion circuit.

Wireless audio and video systems can effectively solve the impact of the family watching TV at night problem. I order a Nissan car stereo channel amplitude converter (AM-STEREO CONVERTER), modified for TV sound radio transmitting and receiving radio with FM stereo ear plugs, the effect is very good.

This machine is a small difference between the actual transfer, the receiving AM stereo signal, turn FM stereo transmitter. In this study, only FM and FM stereo transmitter encoding NJM2035D Circuit, other circuits abandoned. NJM2035D typical application circuit shown in Figure for reference.

Figure R1, C3, R3 and R2, C4, R4, respectively, constitute the left and right channels of the pre-emphasis network, NJM2035D FM stereo coding for the dedicated IC, a 14-pin DIP package, L, R audio signal by the pre-emphasis network, respectively, into  legs and feet, foot external 38kHz crystal oscillator signal generated by L, R signal division multiplex modulation generated stereo composite signal output from the feet, the other by an internal 38kHz oscillator signal frequency divider by the derivative 19kHz pin from the output frequency signal. Composed of Q1 and related components, high-frequency oscillator in the 88 ~ 108MHz frequency range. Composite signal and the 19kHz stereo pilot signal, respectively, through R5, C9, R6 after the overlay, and then by C10 coupled to the base of Q1 high-frequency oscillations of the FM signal, modulated high frequency signal launched into the air by the antenna.

Conversion process: open the case, the board found across the line in J5, J5 that is cut off AM radio IC1 (LA1130) power supply, find IC3 (HA17324) next to the R33, R32, R33 welded open end marked O, R32 without O’s end tag, respectively, in R33, R32 end of the cascade provoked a small 1µF tantalum capacitor, resistor, capacitor positive and negative back then solder a stereo shielded cable LINE IN jack (RCA jack for this to be self-installed.) 0.5m long cable access series with 30pF capacitors to find the most transistor Q5 of the e welding as a transmitting antenna. Remove the power from the radio scrap seat installed in the back left, then the power red positive, black to negative power source. After checking correct 3.5mm plug with a 9V DC power supply power to the stereo transmitter.

Effect: Test CD machine and the machine connected with the German health FM stereo receiver ear radio, tunable in the vicinity of a 99MHz clear stereo sound signal, firing frequency stability, high signal to noise ratio, good sound quality, I live in the third floor, in the Downstairs the reception of sound within 20 meters is still clear.

Note: 1. Such as launch an FM radio frequency and the same frequency, appropriate adjustment L1 (case there is a small hole right above) can be avoided. 2. The transmitter placed 0.5m away from the TV where the TV without any effect, if less than this distance, there will be interference on the TV. 3. DC power supply must choose good quality, the best regulator plus one AN7812. 4. Do not increase transmission power, so as not to affect the other equipment around.