Simple remote wireless FM microphone

Looking for a wireless microphone with a long transmission distance, high sensitivity to picking up sound, no frequency running for a long time, simple and easy debugging, and low cost, many fans are eager to hope. The single-tube long-range wireless FM server introduced in this article has the above characteristics:
Since the loop antenna L1 for transmission doubles as an oscillating coil, what flows in the antenna is a high-frequency current that resonates synchronously with the oscillating cheek rate, so it is always in the optimal transmission state. After practice, the transmission distance is about 100-150m in the open field (the receiver uses TOLYl781 pocket radio, the antenna of the machine is extended to the receiving distance that can be reached when it is 0.8 meters). In contrast, when the working voltage, working current, and transmission frequency are equal, L1 is replaced by a common helical coil, and the oscillating transistor collector is connected to a whip antenna with a 5P capacitor to 0.8m in length for the launch experiment. The transmission distance of this kind of transmission method is almost the same. It proves that the transmission efficiency when the built-in loop antenna doubles as the oscillating coil is quite high. Built-in loop antenna, made of enameled wire with a length of 160mm and a diameter of 1mm, made of a metal ring or box shape, embedded in the chassis; adjust the capacitor C3 to make the transmission frequency fall between 88-108MHz, so that it can be received by the FM radio . 'When the battery voltage changes between 1.2-2V, long-term work, the transmission frequency of this circuit is stable. When the battery voltage is 1.5V, the whole. Machine work-current is about 2.5mA. When debugging, keep your hands away from the loop antenna, and don't approach metal objects when placing it, so as not to affect the oscillation frequency and emission distance.

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