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9V fm transmitter circuit

This fm transmitter circuit is a very simple and require few external components and operates in FM band above 100 MHz.
This fm transmitter circuit needs to be powered from a 9 volts battery or from another 9 volts regulated power supply .
The tuned coil L1, has two output tapping for the antenna connection, marked "A" and "B". These are both low-level outputs and you choose which tapping you want to use ( stable low range, or more unstable but higher range).
Tap B (2.5%) takes just a very small portion of signal from the oscillator circuit and therefore gives a very frequency stable transmitter. The output level (around 2.5mW) and range are therefore somewhat reduced.
Tap A (10%) delivers very much more power (around 10mW) to the antenna load. This gives you a greater range, but at the expense of frequency stability.
All component leads should be kept as short as possible. The LINK wire on the PCB should
lay flat on the PCB. Use the cutoff from a resistor leg.
Antenna length for circuit diagram transmitter varies with frequency for optimum distance: 90MHz 80 cm, 95MHz 75cm, 100MHz 70 cm, 105 MHz 68 cm.

The frequency determining elements (L1, C5 and C6) form a simple LC tuned oscillator. The inherent problem with this type of circuit diagram transmitter is that any external load (antenna) will change the operating frequency.

Electronic Circuits: 
Circuit Diagram: 
9V fm transmitter circuit design using transistors


Please I have problem with my 2 transistor transmitter the signal is not stable pls help me.

I think that circuit can be influenced by external electromagnetic fields. try to keep coil away from magnetic cores and electromagnetic fields.

The collector of Q1 is direvt coupled to the base of Q2 through the 1k resistor R5. Any change of temperature or bias is amplified by Q1 and that changes the frequency. The two Qs should not be direct coupled, the audio should be coupled to Q2 through a capacitor. The circuit is not a good design. Thanks for the informative website.