FM Transmitter

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Here is the schematic, PC board pattern, and parts placement for a low powered FM transmitter. The range of the transmitter when running at 9V is about 300 feet. Running it from 12V increases the range to about 400 feet. This transmitter should not be used as a room or telephone bug.

Schematic

PC Board Layout and Parts Placement

Parts

Part	Total Qty.	Description	Substitutions
C1	1	0.001uf Disc Capacitor
C2	1	5.6pf Disc Capacitor
C3,C4	2	10uf Electrolytic Capacitor
C5	1	3-18pf Adjustable Cap
R1	1	270 Ohm 1/8W Resistor	270 Ohm 1/4W Resistor
R2,R5,R6	3	4.7k 1/8W Resistor	4.7K 1/4W Resistor
R3	1	10k 1/8W Resistor	10K 1/4W Resistor
R4	1	100k 1/8W Resistor	100K 1/4W Resistor
Q1, Q2	2	2N2222A NPN Transistor	2N3904, NTE123A
L1, L2	2	5 Turn Air Core Coil
MIC	1	Electret Microphone
MISC	1	9V Battery Snap, PC Board, Wire For Antenna

Notes

L1 and L2 are 5 turns of 28 AWG enamel coated magnet wire wound with a inside diameter of about 4mm. The inside of a ballpoint pen works well (the plastic tube that holds the ink). Remove the form after winding then install the coil on the circuit board, being careful not to bend it.

C5 is used for tuning. This transmitter operates on the normal broadcast frequencies (88-108MHz).

Q1 and Q2 can also be 2N3904 or something similar.

You can use 1/4 W resistors mounted vertically instead of 1/8 W resistors.

You may want to bypass the battery with a .01uf capacitor.

An antenna may not be required for operation.

A thanks goes out to Mike_Springer@iname.com for cleaning up the original image once displayed on the page. It looks a lot better now!

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Comments

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Ammad Ali FM Transmitter Sunday, January 31, 2010 3:02:36 PM

what can i do to increase the range of FM transmitter?

Trance FM Transmitter Monday, January 11, 2010 7:31:55 PM

I'm fairly new to electronics and in trying to build this circuit I came across a few answers. You absolutely need an adjustable capacitor with the recommended value to tune your cicuit to the desired FM frequency. It is super sensitive so grab a radio and look for what frequency you are on. Also after the circuit has been on for a while the frequency changes when heat builds up so you have to keep adjusting it. I also found that putting a 10k and 4.7k resistor in series to the + terminal helped my electret mic(from Radioshack) pick up more sound. I'm sure you can use 26AWG or 30AWG. Best advice is get a breadboard and test every question you have. I am not finished with this circuit yet. I still have alot to learn. I'm sure you can hook up any output instead of a microphone but I will try it.

SUBBHHAJIT More powerful FM Transmitter Tuesday, January 05, 2010 12:40:19 PM

Can you give me a more powerful (range: around 1-2 km) Fm transmitter circuit diagram. It could be very useful for transmitting songs from my mp3 player to my easy portable mobile.

arjie FM Transmitter Friday, November 20, 2009 8:15:37 PM

hey, i would like to know what is the frequency used in this fm transmitter. I would like to build my fm transmitter for my design project and what is its gain and output power? can you give me a complete computation about the above questions i have already mentioned?

ERIC ANSAH FM Transmitter Monday, November 02, 2009 11:00:54 AM

HI, WANT TO KNOW THE DIFFERENCES BETWEEN FM TRANSMITTER AND AM MODE OF TRANSMITTER AND HOW FM TRANSMITTER CAN HAVE A STABLE GAIN

cabelm FM Transmitter Friday, October 16, 2009 6:03:40 AM

I build it, and it works realy good. Thanks

anonymous FM Transmitter Friday, October 02, 2009 1:12:33 AM

How can i produce a desired frequency?? What parameters should i change to get a lower frequency radio wave?

saad FM Transmitter Sunday, September 20, 2009 12:36:57 PM

hi is this necessery to make the circuit as shown on the fig 3 of pcb mean that can the position of components can be changed??? if not then why??? can i make this on varo board?? sorry for any grammer mistak saad pakistan

BADAR SUHAIL FM Transmitter Sunday, September 13, 2009 3:49:06 AM

please can somebody tell me if the indcutor specifications do not meet.i.e if 28 AWG enamel coated magnet wire is not available. can i use a simple coil and wind it. also it is nessecary to use a variable capacitor?

Nitin FM Transmitter Saturday, September 12, 2009 4:29:44 PM

May I connect something else than electret microphone? Maybe a plug from computer?

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Ammad Ali	FM Transmitter	Sunday, January 31, 2010 3:02:36 PM
what can i do to increase the range of FM transmitter?
Trance	FM Transmitter	Monday, January 11, 2010 7:31:55 PM
I'm fairly new to electronics and in trying to build this circuit I came across a few answers. You absolutely need an adjustable capacitor with the recommended value to tune your cicuit to the desired FM frequency. It is super sensitive so grab a radio and look for what frequency you are on. Also after the circuit has been on for a while the frequency changes when heat builds up so you have to keep adjusting it. I also found that putting a 10k and 4.7k resistor in series to the + terminal helped my electret mic(from Radioshack) pick up more sound. I'm sure you can use 26AWG or 30AWG. Best advice is get a breadboard and test every question you have. I am not finished with this circuit yet. I still have alot to learn. I'm sure you can hook up any output instead of a microphone but I will try it.
SUBBHHAJIT	More powerful FM Transmitter	Tuesday, January 05, 2010 12:40:19 PM
Can you give me a more powerful (range: around 1-2 km) Fm transmitter circuit diagram. It could be very useful for transmitting songs from my mp3 player to my easy portable mobile.
arjie	FM Transmitter	Friday, November 20, 2009 8:15:37 PM
hey, i would like to know what is the frequency used in this fm transmitter. I would like to build my fm transmitter for my design project and what is its gain and output power? can you give me a complete computation about the above questions i have already mentioned?
ERIC ANSAH	FM Transmitter	Monday, November 02, 2009 11:00:54 AM
HI, WANT TO KNOW THE DIFFERENCES BETWEEN FM TRANSMITTER AND AM MODE OF TRANSMITTER AND HOW FM TRANSMITTER CAN HAVE A STABLE GAIN
cabelm	FM Transmitter	Friday, October 16, 2009 6:03:40 AM
I build it, and it works realy good. Thanks
anonymous	FM Transmitter	Friday, October 02, 2009 1:12:33 AM
How can i produce a desired frequency?? What parameters should i change to get a lower frequency radio wave?
saad	FM Transmitter	Sunday, September 20, 2009 12:36:57 PM
hi is this necessery to make the circuit as shown on the fig 3 of pcb mean that can the position of components can be changed??? if not then why??? can i make this on varo board?? sorry for any grammer mistak saad pakistan
BADAR SUHAIL	FM Transmitter	Sunday, September 13, 2009 3:49:06 AM
please can somebody tell me if the indcutor specifications do not meet.i.e if 28 AWG enamel coated magnet wire is not available. can i use a simple coil and wind it. also it is nessecary to use a variable capacitor?
Nitin	FM Transmitter	Saturday, September 12, 2009 4:29:44 PM
May I connect something else than electret microphone? Maybe a plug from computer?