One of the most important parts of the circuit is capacitor C7, a 0.1pF capacitor. Finish once you have approximately 1 inch of twisted wire and cut the looped end off, keeping approximately 1/2 inch of twisted wire for the capacitor and 1/2 inch of untwisted wire for the connections. To construct this tiny value capacitor, bend a 4 -inch piece of 24 -gauge insulated wire in half and twist the wire as though it was a rope starting 1/2-inch from the open end. The coil that looks better could be utilized in the tank circuit (L1), while the other could be used in the next one you make.Ĭapacitor C6, the other hand-made component, is included within the oscillator feedback. Remove the coil you've created and remove the two coils from one another. Two parts of 24 gauge insulated wire, arranged side by side, are wound with 6 turns around a pencil to make the inductor. This basic transmitter circuit just needs a couple of hand-made parts: coil L1 and capacitor C6, both of which may be manufactured just with wire and a regular pencil as a coil shape. The 10 uF capacitor, C1, must be attached to the microphone/R1 junction in the center of the board, orientated as indicated on the diagram. Solder the connection between R1 and the microphone's positive lead. Next, connect the microphone wires to the board, being careful that the MIC's ground lead can be soldered to the ground line of the board. Move down to the bottom bus after passing through the board. Ensure that you mount the resistor vertically adjacent to the positive supply line and twist the connection to the board. The bias voltage for the microphone is provided by a 1K resistor (R1). To begin, use bare wire to create two power supply lines on the board: the positive supply from the battery would be on upper edge, and the negative (ground) should be on the bottom edge of the board. That way, you'll have more than enough area to play with while still producing a compact item. You'll need a strip of perfboard which is 12 holes broad and 30 holes long. You may begin on the left side of the diagram and work our way to the right. In general, you'll would like the transmitter to be as tiny as feasible. You should arrange the parts on the pcb in a pattern that resembles the schematic. Part spacing isn't important, but part location is. This 200 meter range FM transmitter circuit is made out of perforated building board with 0.1-inch spacing between holes. C5 is a 6-50 pF trimmer capacitor that tunes the oscillator tank circuit, while C4 sends the RF from the oscillator to ground to keep it stable. The DC operational bias of Q2, an additional 2N2222 that serves as the transmitter's oscillator and modulator, is adjusted via resistors R7-R9. This will allow you to keep the level of distortion on too loud inputs under control. The input to the RF stage is limited by resistor R6, whose value may be modified as needed to restrict the loudness of the input. The oscillator is made up of the transistor Q2 and its related circuitry (C5 and the inductor) that works between 80 and 130 MHz.īecause the oscillator is voltage-controlled, the audio voltage delivered to Q2's base modulates it. Q2's base receives the enhanced AC voltage from Q1. C3 improves the AC response to the audio voltage, while C2 blocks the DC bias and links the AC to the next stage, which is where the RF action occurs. Q1's DC operational bias is adjusted by resistors R2-R5. Referring to the circuit diagram below, an electret microphone picks up sounds from the surroundings, which Q1 amplifies. Distance Range: Over 100 meters Design#2 200 Meters Transmitter Circuit
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