Simple FM transmitter

This transmitter can be tuned to the FM broadcast band, 2 meters, or other VHF bands by changing C5 and L1. The values provided for C5 and L1 will position the frequency within the FM broadcast band. L1 consists of 4 turns of #20 enameled wire, air-wound, with a diameter of 0.5 inches, a length of 5mm, and is center-tapped. The microphone used is of the electret type, and the antenna is made of 18 inches of any type of wire. It is advised to keep all leads as short as possible to minimize stray capacitance. The range of the transmitter extends for several hundred yards.

The described transmitter operates by utilizing a combination of components that allow it to function effectively within the FM broadcast band and other VHF frequencies. The tuning mechanism involves a variable capacitor (C5) and an inductor (L1), which together determine the resonant frequency of the circuit. The inductor L1, constructed from 4 turns of #20 enameled wire, is air-wound to minimize losses and improve efficiency. The specific dimensions of the inductor, with a diameter of 0.5 inches and a length of 5mm, indicate a compact design that is conducive to portable applications.

The electret microphone serves as the audio input for the transmitter, converting sound waves into electrical signals. This type of microphone is favored for its low power requirements and reasonable sensitivity, making it suitable for various applications, including personal communication devices. The audio signals from the microphone are modulated onto the carrier frequency generated by the tuned circuit.

The antenna, measuring 18 inches, is crucial for effective transmission of the modulated signal. The choice of wire type for the antenna can vary, but it is essential that the length is appropriate for the frequency range being transmitted to ensure optimal performance.

To enhance the transmitter's performance, it is recommended to minimize the length of all leads connecting the components. This practice reduces stray capacitance, which can interfere with the operation of the circuit and degrade signal quality. The effective range of the transmitter is reported to be several hundred yards, indicating its potential for various applications in short-range communication. Overall, the design emphasizes simplicity, efficiency, and adaptability to different frequency bands through component adjustments.This transmitter can be tuned to the FM broadcast band, 2 meters,-or other VHF bands by changing C5 and Ll. The values given for C5 and Ll will place the frequency somewhere in the FM broadcast band. Ll is 4 turns of #20 enameled wire airwound, % inch in diameter, 5mm long and center-tapped. The microphone is an electret type and the antenna is 18 inches of any type of wire Keep all leads as short as possible to minimize stray capacitance. The range of the transmitter is several hundred yards.