How to use 1815 to make a small fm transmitter?
Now to introduce a simple and easy system of small FM transmitter.It is not only full foot firing distance requirements, but also can use microphone and line input sound signal at the same time, to voice in the background.Also joined the modulation circuit monitoring meter, in order to better master and use good transmitter, circuit diagram, see the simple introduction, do you feel it like a radio station equipment more functions. Yes, this small launch machine to help you to easily set up a spare FM radio station! Coverage in the 500 m or so.Echocardiography, act now!
2.Small FM transmitter circuit principle and component selection:
The receiver get signal, and the C1 coupling into BG1 and peripheral circuit into a set of single tube voltage negative feedback amplifier, the voltage signal amplification of weak to enough with U1A amplification circuit input signal after entering U1B.Mixed signals a path R17 to modulation by BG2 field-effect tube and peripheral circuit of test time than LC oscillation device, take an examination of the characteristics of The Times than LC oscillator is a simple, ordinary capacitor three-point oscillator and also has high efficiency and high stability.Good waveform, modulation bandwidth, this to amateur FM transmitter is particularly important.Finally after BG3 a molten amplifier amplification by transmitting antenna to launch, using ordinary FM radio to listen to the radio.Another signal all the way through the amplifier amplification of U1C then through D2 simple wave rectifier with a dc microammeter drive, in the monitoring signal amplitude modulation.It is advisable to use sort system generally not more than 85%.Integrated circuit adopts the LM324, etc Reverse input with SiYun put, forming a single power supply works, both positive phase voltage of the input is set in half of the power supply voltage.Monitoring meter is 200 u, BG1. Choose 2 sc1815 BG3.BG2 3 do2 field-effect tube, D2 1 s2267 varactor adopted.Antenna that USES a quarter wavelength, such as using the telescopic antenna had better not less than one meter.Otherwise will not exceed the time limit effect.