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Long Range FM Transmitter Circuit Diagram

2016-04-01 15:39  
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Here is a  circuits introduction about Long range FM transmitter.The transmitter circuit described here has an extra RF power amplifier stage, after the oscillator stage, to raise the power output to 200-250 milliwatts. With a good matching 50-ohm ground plane antenna or multi-element Yagi antenna, this transmitter can provide reasonably good signal strength up to a distance of about 2 kilometres. The circuit built around transistor T1 (BF494) is a basic low-power variable-frequency VHF oscillator. A varicap diode circuit is included to change the frequency of the transmitter and to provide frequency modulation by audio signals. The output of the oscillator is about 50 milliwatts. Transistor T2 (2N3866) forms a VHF-class A power amplifier. It boosts the oscillator signals’ power four to five times. Thus, 200-250 milliwatts of power is generated at the collector of transistor T2. For best results, assemble the circuit on a good-quality glass epoxy board and house the transmitter inside an aluminium case. Shield the oscillator stage using an aluminium sheet. Coil winding details are given below:L1 - 4 turns of 20 SWG wire close wound over 8mm diameter plastic former.L2 - 2 turns of 24 SWG wire near top end of L1.L3 - 7 turns of 24 SWG wire close wound with 4mm diameter air core.L4 - 7 turns of 24 SWG wire-wound on a ferrite bead (as choke)Long Range FM Transmitter Circuit Diagram