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Remote FM transmitter circuit Introduction

2016-04-05 13:08  
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This article describes a remote FM transmitter circuit. The circuit is simple, inexpensive, and effective. As long as Duokanjibian The schematic can master the principles of it. This circuit is for technical exchanges. Transmitter circuit described here have an additional RF power amplifier stage, the oscillator stage, the increased power output to 200 - 250mW. There is a good match to 50 ohm ground plane antenna or multi-Yagi antenna, this transmitter can provide a fairly good signal strength up to a distance of about 2 km. Circuit based on the transistor T1 (BF494 ) is a basic low-power variable frequency VHF oscillator. A varactor diode circuit comprises changing the frequency of the transmitter and to provide frequency modulated audio signal. The oscillator output of about 50 mW. Transistor T2 (2 n3866) forms a VHF power amplifier. It promotes the oscillator signal power four to five times. Thus 200 - 250mW of power generated collector transistor T2. For better results, assemble the circuit in a high-quality glass epoxy board and the house is placed in an aluminum housing. Shield the oscillator stage using aluminum plate.
Details of the coil winding is given by:
L1 - 4 turn 20 SWG wire close wound in 8 mm diameter plastic front.
L2 - 2 turn 24 SWG ??wire near the top of L1.
L3 - 7 turn 24 SWG ??wire close wound with 4 mm diameter hollow.
L4 - 7 turn 24 SWG wire-wound ferrite beads (choking)
Potentiometer VR1 is for changing the fundamental frequency of the power control potentiometer VR2 is used. For hum free operation, the operator in a 12 v rechargeable battery 10 x 1.2 volt nickel-cadmium batteries. The transistor T2 must be installed on the radiator. Do not turn on the transmitter without a matching antenna. Adjust two parts bricks (VC1 and trends) the maximum transmission power. Adjust potentiometer VR1 to set the fundamental frequency near 100 MHz.



Long range FM transmitter



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