FM Wireless Microphone | Electronic Project Circuits

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FM Wireless Microphone by MAX4467

Here is a very simple, inexpensive and interesting project which provides lot of fun to a home experimenter or hobbyist. This simple transmitter can transmit speech over a short range. It can be used as a simple cordless microphone. The circuit uses two integrated circuits from Maxim. IC1 a MAX4467, is an amplifier raising the microphone signal to a level suitable for frequency modulation (FM). IC2 is a voltage-controlled oscillator (VCO) with integrated varactor (a.k.a. varicap diode). Its nominal frequency of oscillation is set by inductor L1. The inductor value 390 nH provides an oscillation frequency of about 100 MHz. For best performance, L1 should be a high-Q component. L1 may consist of 4 turns of silver-plated wire wound around a 10-mm drill bit, and stretched to a length of about 1.5 cm.

The wire diameter can be anything between 26 SWG (0.5 mm) and 20 SWG (1 mm). No core is used. The MAX4467 is a micro-power opamp for low voltage operation and providing 200-kHz gain bandwidth at a supply current of just 24 µA. When used with an electret microphone, some form of DC bias for the microphone capsule is necessary. The MAX4467 has the ability to turn off the bias to the microphone when the device is in shutdown mode. This can save several hundred micro-amps of supply current, which can be significant in low power applications particularly for battery powered applications like cordless microphones. The MIC-Bias pin provides a switched version of Vcc to the bias components. [...]

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Categories: FM transmitter Tags: crystal FM Transmitter, FM Wireless Microphone

FM Wireless Microphone by BC557

FM Wireless Microphone has been a very popular project with beginners and experienced constructors alike. It has been used inside guitars and as the basis of a remote control system. I do however, receive many requests for a higher powered circuit and better microphone sensitivity. Now I can introduce the new FM Wireless Microphone (v5), which also has a better frequency stability, over 1Km range (under ideal conditions) and is good on microphone sensitivity. This has been achieved by adding an RF amplifier buffer (with 10dB gain) and an AF preamplifier to boost the modulation a little.
Read source: http://w1.859.telia.com/~u85920178/tx/bug5.htm