Abstracts
In electronic communications, the radio frequency spectrum (RF Signal) is widely used in all the modern communication systems. The generation and transmission of RF signal can be accomplished by various modulation techniques. Frequency modulation is such a technique. The communication through cordless & Cell phones, radio and TV broadcast stations, satellite communication systems, Bluetooth module and Wi-Fi is now becoming an essential part of human life. All these systems use RF spectrums for communication. The sound coming out from the modern communicating devices is Frequency Modulated (FM) signals. For noise free communications, frequency modulation is used by all the modern speech communicating devices. The device that is discussed in the paper is a low power, narrowband frequency modulated transmitter which can transmit sound or speech signals around 100 meters with only a 10 cm copper wire as an antenna. The sound quality is very clear and noise free. As, the VHF RF FM transmitter is designed with crystal oscillator, so frequency is fixed at 88.7 MHz. No parasitic effect results in the circuit for the contribution of the crystal.
Keywords : Antenna; biasing; coupling network; frequency multiplier; pre-amplifier; RF power amplifier; VHF RF oscillator.
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