Production of high quality wireless microphone is the desire of many readers, but the amateur to make high performance under the conditions of the receiver is not easy. I open up ways to use scrap cars Shoufang Ji in the FM radio part of the increase in a XR1075 audio processor, redesigned the printing plate, produced a stable and reliable, excellent electrical properties of dual-band wireless microphone transceiver system. Transmitter FM transmitter-specific integrated circuits using BA1404. The electrical and mechanical principles shown below, now the production process are described below.
The figure shows that the circuit consists of four parts, namely, the first frequency, intermediate frequency amplification, audio processing and power supply.
The basic principles of the signal from the antenna sensing head from the feet of FM input, the internal high level, after mixing the oscillator output from the pin 10.7MHz IF signal input from the C1 to T1 after the IF preamplifier filter out by JT1 10. IF signal is sent to the IC1 7MHz feet, by the internal limiting, amplification, frequency audio signal after the demodulation for the output from the pin, from C8 to T2 zoom coupled to the level required to meet the IC3. Audio signal input from the IC3 feet, the inner part of the band after the digital processing delay of the output from the pin. IC1's pin is 2.25V reference voltage source, the output pin for the tuning instructions in this circuit as a mute. The principle is: When the feet are 10.7MHz IF signal input, the pin is low, T3 end, IC3 pin to output audio signals without attenuation; contrary pin is high, power supply by R11, D2, R13 provides bias to the T3, T3 saturated, so the audio signal through T3, c, e pole into the ground, in order to squelch the purpose. L1, C 10.7MHz frequency selective network components, it is also the second in place of the load IC1, C2, C3 for the intermediate frequency bypass capacitor, W1, W2 are the treble and bass audio processor gain adjustment potentiometer, and its principle can be See the "newsletter" in the relevant article.
Installation and commissioning requires FM tuner includes head, removed from circuit boards and tuners, welding under the 10.7MHz filter JT1, IF filter (shape like in the week, the general magnetic cap light blue), TA7640, FM tuner (see photo top right corner of form) and other key components for the standby. According to case size make a printing plate, printing plate should be used epoxy boards and large ground, ready to welding components, T3 and T6 and then adjusted the machine to be installed. Power (in case all the way), IC1's feet measured voltage should be 6.5V or so, FM heads and feet should be 6V, 0.15V or so feet (M47-type table measurement, digital meter measurement was 1.9V), adjust the R1 and R10 to T1, T2 collector voltage is 3V or so. Connected to the amplifier and speaker, if the circuit is normal at this time, speakers should have a larger "rustling" sound, if not rustle, can touch the IC3 are the feet of a screwdriver, T2 base should hum, taking even IC1, and, ,, feet, T1 should be a more sound base "giggle" sound, or should check JT1, L1, IC1 and the surrounding components. Normal rotation of all the first closing of a local FM frequency modulation radio stations, adjust the L1 core to sound clear. Then adjust the transceiver with the microphone frequency (avoid the attention of local radio frequency), and finally with the microphone facing the more familiar music sound better regulation W1, W2 to make clear, natural sound receiver so far, if the microphone to pick up the human voice-based, can be appropriate increase in the treble (adjust W2). Another way to adjust the same way. At this point welding on the T3 and T6, debug auto-mute function, turn off the transmitter, the corresponding TA7640 feet should be high; opening should be low, or to re-adjust L1.
Although not using the crystal oscillator frequency stabilization circuit, but because of the high frequency stability of the first, the wireless microphone transceiver frequency is very stable, there has never been offset from the winter solstice, the author will be two microphones are used to zither and voice, the subjective feeling of very clear and beautiful string zither, voice sound a more visible teeth. As long as the components of quality assurance, the wireless microphone and several hundred thousand dollars to finished machine comparable, of course, interested readers can also IC1, IC2 increase the harmonic generator output in order to improve the clarity of the sound. This machine uses 9.6V rechargeable batteries disposes power, external 16V power supply for battery charging purposes, the R31, D4's role in limiting regulation, so long-term access to an external power supply unit.