Small power FM broadcast transmitter circuit design

This design uses some existing components, comprehensive references. 1881.< 北京报报报 1. 制制制制制文文文文文文发文文文文文文文文文文文In the 108MHz band, the spare time is used to play music. The principle of the circuit is listening. Figure (1) is a power supply portion, and then regulate the mainstream of the city, and obtain a stable 12V DC electrical radio frequency circuit. The RF circuit consists of a high frequency oscillator, a buffer amplifier, a final level power amplifier, and antenna. The high-frequency oscillator is used to generate a carrier frequency signal, and the frequency point is within 88--108 MHz and the frequency of frequency can be changed to change the emission frequency. The radio frequency signal is output from the emitter output of VT1, and the buffer amplifier of VT2, L2, C22, R4, etc. perform power promotion, and can reduce the impact of the end-level amplifying circuit on the oscillator. The final stage is high frequencies amplification, and the radio frequency power is further enlarged, and the C25 is coupled to the transmit antenna radiation to the surrounding space. If the procedure is excessive, if the output signal is excessively large, it is necessary to enter the attenuation resistance to avoid distortion of the sound. The board can be made of copper coplanc, and the distribution capacitance should be paid to the wiring. The figure in the figure is not units in the figure, and it will be "pf" unit, and the high frequency porcelain capacitance is required. VT1 - VT3 uses ultra-high frequency NPN silica tube such as 9018, B>60, ICM = 50mA.fr> = 600MHz.vt3 can also be used in medium power transmitters C2053, BF96S, etc., the emission distance may be further. The L1-L3 is formed from 4 to 4 laps with a 3.8 mm enamel wire. The antenna is a tensile antenna, which has a length of 1/4 (or 1/2) of the frequency wavelength. If the transmit frequency is 100MHz, the antenna length is 0.7m (or 1.5m) Install step by step when making it. The radio frequency portion is first loaded, the buffer amplifier, the hut-mounting distance of the regulation of L1 has fallen in a non-table, and the black list of the pointer type is in contact with the collector of VT2, and the adjustment L2 makes the pointer to the maximum deflection, (ie power maximum). If there is a tab, you can wrap it together until you don't play. The same method is adjusted to adjust the L3 to make the last output power. The FM radio is used to search the transmitted signal at 10 meters from the transmitter. It is approximately estimated that the transmit frequency is estimated, and then the antenna is connected, and the length is appropriately adjusted, it can be put into use. When the power supply voltage is 12V (in fact, the higher the 6-15V can work normally, the higher the voltage, the distance is far from the distance, the operating current is only about 45mA, the transmit frequency is about 104MHz, placed in the third floor balcony, there is too high In the case of a building block, it is received with a popular machine (internal chip CXA1019M), and the distance is up to 1000 meters.