FM Transmitter

Assalam o Alaikum !

Today I want to share my first electronic project in my student life . which is a simple FM Transmitter.

Requirements :

1- Breadboard
2- Resistors , Capacitors as in figure
3- 9 volt DC Battery
4- Mic

Note: Don't buy Inductor as it wont work,until its in wounded wire shape and take a good mic with long legs :)

You have to make it yourself. You have to take a 15/22 gauge wire and wound it on anything with less diameter(pencil,pen,etc) or You can make it through this formula.

 L  = [d² n²] / [18d + 40l]

• Where’ L ‘  is the inductance in Micro Henries [µH]
• ‘d’ is the diameter of the coil from one wire centre to another wire centre. It should be specifies in inches.
• ‘l’ is the length of the coil specified in inches.
• ‘n’ is the number of turns.

Mine worked within 5,6 turns of 15 gauge wire on a HB-2 pencil. (Can vary Definitely :) )

Steps:

1- Wire all these components on the breadboard and importantly this circuit should take as little place as possible, try to make it congested and turn the long legs of the components into small legs ( By cutter ofcourse :) )

2- Now connect the DC battery and Tune the radio (e.g in Cellphone ), it would automatically tune a station without any voice output( means circuit is working) , Now you can sing Opera on the Mic :D..

3- You can introduce antenna with inductor capacitor combination (as in figure ) to extend the range.


Description :

1- R1,R2,R6 are DC biasing resistors for keeping the transistor Q1 forward Biased.
2- C1 is used to remove any DC signal in AC signal(voice from mic).
3- Transistor Q1 is just amplifying the voice signal which is in milivolts (mv)
4- Then again R4,R5,R8 are DC biasing resistors for Q2.
5- Now Q2 is amplifying the coming voltage and C7 and inductor are performing the Frequency Modulation.

Precautions :

Wiring should be congested , Mic should be connected with right polarity with the DC battery , Receiver should not be touching the inductor when the transmitter is on , Battery should at least be 6 volts.

You can use Circuit Maker from National Instruments .