Self-made low-power FM radio transmitter


I used the components on hand, comprehensive reference <<Beijing newsletter>> other press articles related to production, made a long-range FM radio transmitter operating in the 88 - 108MHZ band, the spare time to play Music.

Circuit now see the photo. Figure (1) power supply section, will then be rectified mains step-down regulator to obtain a stable 12V DC for use of radio frequency circuit. RF circuit consists of high-frequency oscillator, buffer amplifier, the final stage power amplifier and antenna. High-frequency oscillator used to generate the carrier frequency signal, frequency falls 88 - 108MHZ, the sense of volume and complete the frequency of firing frequency can be changed. RF signal output from the emitter VT1, sent to the VT2, L2, C22, R4 composed of buffer amplifier power increase and reduce the final stage of the oscillator amplifier circuit. Last Stage for the high-frequency C band amplification, further amplification of the RF power, coupled by C25 to the transmitting antenna to the surrounding space radiation. The connections are the source if the output signal amplitude is too large, the required weak resistance in series in order to avoid sound distortion.

Available Bonded Copper circuit board manufacture, cabling, distributed capacitance effects in mind. No unit of capacitance figure numbers marked, should be to "pF" as a unit, to high-frequency capacitance tiles. VT1 - VT3 with UHF NPN silicon tube, such as 9018, B> 60, Icm => = 600MHZ.VT3 can also use the power transmitting tubes C2053, BF96S, etc. may be farther away from launch. L1-L3 enameled with 00.8mm in the 04mm screw on the pen made of a tightly wound four laps prolapse. Antenna rod antenna, the length of the frequency wavelength of 1 / 4 (or 1 / 2). Such as launch frequency of 100MHZ, the antenna length 0.7m (or 1.5m)

Production should be step by step install. RF part of the first loaded oscillator, buffer amplifier, adjust the distance between the turns L1 frequency falls to no station, we use a pointer type multimeter black table document contact with the collector VT2, adjust L2 pointer deflection to the maximum amplitude, (ie power maximum). If there is the phenomenon of playing table, the table document can be intertwined, until the table is not playing up. Re-use the same method to adjust the L3, so that the maximum final output power. FM radio with 10 meters away from the transmitters transmit signals over the local search, some estimate the emission frequency, connect the antenna properly adjusted length, can be put into use.

12V supply voltage measured machine (actually 6-15V can work within, the higher the voltage, the farther away), 45mA operating current is only about firing frequency of about 104MHZ, placing third floor balcony, in the absence of high building block of the case, with the universal machine (the internal chips CXA1019M) receiving, from as much as 1,000 meters.





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