This is a circuit for transmitter that can be used in doorbell circuit. This circuit is a simple form. The circuit is based on three transistor. This is the figure of the circuit;
The 303MHz oscillator consists of a self-oscillating circuit made up of the coil on the PC board and a 9p (9 puff) capacitor (actually 4p and 5p in parallel). The circuit starts-up by the transistor producing noise. This rising-and-falling signal on the collector is passed to the parallel tuned circuit (the tank circuit) and the base sees a very smooth sine wave at a frequency of 303MHz. This sine wave is then amplified by the transistor and this is how the 303MHz frequency is generated. Now we come to the purpose of the 15microhenry choke on the tank circuit. When the circuit oscillates, it takes a larger and small amount of current. This current passes through the choke and the turns produce a back-emf or back voltage that fights against the flow (change) in current. The end effect is a voltage created at the point where the choke is connected to the track-work on the board. This effectively allows the track work to produce a waveform and since the frequency of this wave is very high, a percentage of the energy is radiated into the air as electromagnetic energy. The choke allows the track-work to effectively rise and fall while providing a very low resistance path for the flow of current during certain parts of the cycle.
The 303MHz oscillator consists of a self-oscillating circuit made up of the coil on the PC board and a 9p (9 puff) capacitor (actually 4p and 5p in parallel). The circuit starts-up by the transistor producing noise. This rising-and-falling signal on the collector is passed to the parallel tuned circuit (the tank circuit) and the base sees a very smooth sine wave at a frequency of 303MHz. This sine wave is then amplified by the transistor and this is how the 303MHz frequency is generated. Now we come to the purpose of the 15microhenry choke on the tank circuit. When the circuit oscillates, it takes a larger and small amount of current. This current passes through the choke and the turns produce a back-emf or back voltage that fights against the flow (change) in current. The end effect is a voltage created at the point where the choke is connected to the track-work on the board. This effectively allows the track work to produce a waveform and since the frequency of this wave is very high, a percentage of the energy is radiated into the air as electromagnetic energy. The choke allows the track-work to effectively rise and fall while providing a very low resistance path for the flow of current during certain parts of the cycle.
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