![]() ![]() For this circuit, the coil radius was selected as 0.26 inches (outer diameter) and 0.13 inner diameter. Then only the inductor resonates in the 88-108 band FM frequency. The length, inner diameter, number of turns etc are the important parameters to be considered while making the inductor. ![]() The inductor used in the circuit is a hand made coil using 22 SWG (Standard Wire Gauge) enameled copper wire. Pin assignment of 2N 2222 A is 1 Emitter - 2 Base - 3 Collector (EBC) from the front side (Flat side on which the number is printed). So maximum power output should be around 125 milli watt. Over powering of 2N 2222A can generate heat and destroy the device. It has maximum power rating of 0.5 Watts. The given values are necessary for the 2N 2222A transistor.ĢN 2222A is the common NPN transmitter used in general purpose amplifications. The voltage divider R1 and R2 limits the base current of T1 and R3 forms the emitter current limiter. Variable resistor VR1 restricts the current through the MIC. A capacitor between 4 and 10 PF is necessary. Presence of the capacitor C3 prevents this decay. When the tank circuit vibrates for long time, the frequency decays due to heating. As long as the current exists across the inductor coil L1 and the Trimmer capacitor, the tank circuit (Coil-Trimmer) will vibrate at the resonant frequency. Capacitor C3 across the transistor T1 keeps the tank circuit vibrating. Capacitor C2 (0.01) act as the decoupling capacitor. A large value capacitor induces bass (low frequencies) while a low value one gives treble (high frequencies). ![]() The 4.7 uF capacitor isolates the microphone from the base voltage of the transistor and only allows alternating current (AC) signals to pass. C1 modulates the current to the base of transistor. Sleeving the MIC inside plastic tubing can increase its sensitivity enormously.Ĭ1 is the first decoupling capacitor impedes the different frequencies of speech signals. The condenser MIC should be directly soldered on the PCB to get maximum sensitivity. Variable resistor VR1 adjusts the current through the MIC and thus determines the sensitivity of MIC. The diaphragm inside the MIC vibrates according to the air pressure changes and generates AC signals. The condenser MIC is used to pick up the sound signals. The design details of each component are as follows. The circuit diagram shown below is that of a Single transistor FM transmitter with a range of 30-50 feets and 100 – 125 milli watt output.Ĭoil Specification - 5 Turn 22 SWG Enameled Copper WireĬoil Length 0.25 Inch - Diameter 0.265 Inch Coil diameter, length, number of turns and gauge of the wire used for coil winding. Transmitter frequency, output power and range of transmission. The important parameters for the optimum performance of an FM transmitter are :ġ. Length of the Antenna used to transmit the frequency. Even a slight change in the coil specification or slight change in the variable capacitor value can shift the harmonic frequency instead of the 88-108 MHz FM band.Ģ. Tuning of the FM transmitter to the desired frequency. Design Considerations The performance of an FM transmitter depends on two important aspects.ġ. The Note given here explains how a simple FM transmitter is designed and assembled. Designing and assembling an FM transmitter is a difficult task. Usually 87.5 - 108.0 MHz is used to transmit and receive the FM signals. Throughout the world, the broadcast band falls within the VHF part of the radio spectrum. FM is commonly used at VHF radio frequencies for high-fidelity broadcasts of music and speech. You can listen to the audio on an FM radio by tuning to 90MHz frequency band.In telecommunications, frequency modulation (FM) conveys information over a carrier wave by varying its frequency. Connect 12V DC regulated power supply across connector CON1.Ĭonnect the audio input at JACK1 from a computer, music player or cellphone. 3: Components layout for the PCBįor downloading PCB and component layout PDFs: Click hereĪudio quality of the transmitter is decent, and fidelity is good enough for music. 2: PCB layout for the simple FM transmitter Fig. Use a shielded cable for input audio connection for hum-free signals. After assembling the circuit on the PCB or veroboard, enclose it in a suitable plastic box. Construction and testingĪ PCB layout for the simple FM transmitter is shown in Fig. Use an 83cm-long piece of wire for the antenna. The transmitter accepts audio input from such external devices as a computer, music player or cellphone. Potmeter VR1 sets frequency deviation and should be adjusted for best sounding audio and low distortion. Its frequency modulates the oscillator by varying the capacitance of varactor diode D1, which is connected in series with XTAL1 via resistor R2. The audio amplifier formed around IC1 has a gain of twenty.
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