FM Transmitter for car

 

 

10 Simple FM Transmitter Circuits Explained

An FM transmitter circuit is a high frequency wireless device which is able to transmit voice signals into atmosphere so that it can be received by a corresponding FM receiver circuit for reproducing the voice signals in a loudspeaker.

Here we’ll discuss how to build small FM transmitter circuits using 10 different methods, one that consists of wire link from the transmitter to the receiver, and the other which is completely wireless and can be used to eavesdrop a particular conversation over a range of about 30 meters, over an ordinary FM radio..

The above extraordinary capabilities have forced the legal authorities to enforce stringent laws against the use of these transmitters without permission, so before you make and use one of these make sure you have all the legal formalities completed.

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Wireless Design:

I will begin with a transmitter which I have actually built numerous number of times and tested it thoroughly. Subsequently I am going to discuss more such designs which were selected from other websites online.

The sent signals can be received over any standard FM radio, tuned accurately to the respective frequency.

The above shown wireless FM transmitter circuit is basically a small RF transmitter built around a single transistor.

The circuit functions quite like a Colpitts oscillator incorporating a tank circuit for the generation of the required oscillations.

The frequency mainly depends on the positioning and the values of the inductor, C1, C2 and C3. The coil turn distance and diameter may be manipulated a little for optimizing best response over the FM receiver.

A small antenna in the form of a 3 inches wire may be attached at the shown point for making the “bug” highly responsive and generate distortion free signals.

Circuit Diagram

Parts List

• R1 = 3k3,
• R2 = 100K,
• R3 = 470 Ohms
• C1 = 10 pF,C2 = 27 pF
• C3 = 27pF,
• C4 = 102 disc
• C5 = 10uF/10V,
• Mic = condenser mic
• T1 = BC547
• L1 = 3 to 4 turns of 22SWG super enamel copper wire, 5 to 7 mm diameter, air corePlease refer the scanned image of the prototype for getting an idea regarding the coil dimensions.

Now let's discuss a few FM transmitter circuits which can be built using different configurations and features.