This is FM transmitter circuit without Coil, using inverter digital IC as main and controlled frequency is precise by a crystal.
In Figure 1 is RF oscillator circuit which use an inverter IC1/2 and ceramic crystal filter 10.7 MHz to use drive IC1/4 – IC1/6 by through IC1/3.
When inverter in parallel form this impedance output is low. Thus, they can drive directly an antenna.
And the output of IC1/4 – IC1/6 is a square wave. Which has much more internal harmonic. The harmonic number 9 of frequency 10.7 MHz (96.3 MHz) will take place at the center of the FM band.
The IC1/1 is an audio amplifier which signals from the microphone will be amplified and will send to a varicap diode. This signal causes the capacitance of the varicap diode changed and make also oscillator frequency changes. Thus, its occurs modulation frequency.
Part you will need
Resistors ¼ W +-5%
C1, C3: 0.1uF 50V Polyester capacitors
C2: 10uF 25V Electrolytic capacitors
C4: 100pF 50V Polyester capacitors
C5: 100uF 16V Electrolytic capacitors
C6: 22pF 50V polyester capacitors
C7: 0.001 uF 50V polyester capacitors
D1: Varicap diode
Condenser Micro phone
Ceramic crystal filter 10.7 MHz
Note: You can buy ceramic filter here!
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