Before making electronics circuits its good practice to simulate circuit in electronics circuit simulation software such as Proteus Professional software. Here a demonstration of simulation of FM transmitter circuit in Proteus Software is shown. The FM transmitter is designed to operate at 100MHz.
FM Circuit Schematic
The following shows the FM circuit diagram along with the component values.
In the above FM circuit, the audio enters into the circuit via the electret microphone(MIC) whose one side is pulled up using 15KOhm resistor(5KOhm to 10KOhm pull-up will also work). The audio is coupled into the audio pre-amplifier made up using the BC547 Q1 BJT transistor using the 22nF C1 coupling capacitor. The pre-amplifier circuit is biased using self bias technique(see Self Biased BJT amplifier) with the resistor R3 and R2. The amplified audio signal is then coupled into the FM modulator or mixer made up of the transistor Q2 BC547 BJT transistor via the coupling capacitor C2. The BJT mixer performs two functions- one is that it is configured as a LC Colpitts oscillator which generates the local carrier signal with frequency in the FM frequency range 86MHz to 108MHz. This LC oscillator is made up of the inductor L1, C3 and C4 capacitors along with the amplifier components(the transistor Q2, biasing resistors R4 and R5). The inductor is a copper coil of 10 turns. The amplified audio signal enters the FM modulator via the capacitor C2 and mixes with the locally generated carrier signal from the oscillator thus generating FM signal at the collector of Q2. This signal is then coupled to the antenna using the capacitor C5. The size of the antenna is about 25 cm.
PCB Layout
The Proteus software is used to convert the FM circuit into PCB layout which is shown below.
The above PCB layout is then printed on copper board. A full tutorial on how to make PCB at home is shown in the tutorial .
3D View of FM transmitter
The following shows 3D view of the expected FM transmitter design in Proteus.
FM transmitter
The following shows the completed FM transmitter simulated in proteus.
Video Demonstration of FM Transmitter
Watch the following video that demonstrates how to design and simulate the FM circuit in Proteus.
Summary
This tutorial showed how to simulate FM transmitter circuit in Proteus Professional electronics design software. For actual PCB design of this FM transmitter and component population see the tutorial How to make FM Transmitter. The tutorial shows how the circuit works and how to actually build and test the FM transmitter. It shows how to create the schematic and the PCB layout and 3D prototype view of the designed system.
