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Long-term FM Transmitter

2016-04-05 15:21  
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Transmitter power output is very low because there is no amplifier increases. Using the RF transmitter power amplifier. By using the 50 ohm antenna, this transmitter has a power good signal to within about 2 miles. This transmitter uses the transistor T1 (BF494) as a low-frequency VHF oscillator. Diode is used to change the frequency of the transmitter and to provide frequency modulation. The results of the oscillator is about 50 milliwatts. Transistor T2 (2N3866) is a Class A VHF power amplifier. Transistor can increase singnal oscilator four to five times. With so 200-250 milliwatt of power produced at the collector of transistor T2. The following is a schematic drawing:

long term FM transmitter1 Long term FM Transmitter

Coil winding details are given below:
L1 – 4 changes of 20 SWG wire close wound over 8mm diameter plastic former.
L2 – 2 changes of 24 SWG wire near top end of L1. (Note: There is no core (ie air core) is used to coil on top)
L3 – 7 changed from 24 SWG wire close wound with 4mm diameter air core.
L4 – 7 changed from 24 SWG wire-wound on ferrite beads (as Choke)
VR1 potentiometer used to vary the fundamental frequency while Potentiometer VR2 is used as power control. Hum-free to operate, operate the transmitter on the 12V battery can be recharged from 10 x 1.2-volt Ni-Cd cells. Transistor T2 must be mounted on the heat sink. Do not switch on the transmitter without a matching antenna. Adjust both trimmers (VC1 and VC2) for maximum transmission power. Adjust Potentiometer VR1 to set the fundamental frequency near 100 MHz.

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