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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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?

Viraj Mehta FM Transmitter Thursday, September 03, 2009 7:54:05 AM

I want to know the specifications and uses of all the components used in this circuit. Please anybody send me minute details of the components and their purpose.Also I WANT TO KNOW ABOUT THE 5.6uF CAP. AND POSSIBLY A SUBSTITUTE AS ONE IS NOT AVAILABLE PRESENTLY.SECONDLY I WANT THE DETAILS ABOUT THE WORKING OF THE INDUCTOR COILS.These two are primary objectives and then the rest of the other components. Please somebody ler me know about the components' working and oblige.Thanks.

Bojan Andrejek FM Transmitter Saturday, August 22, 2009 11:20:08 AM

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

scode FM Transmitter Thursday, July 23, 2009 12:45:27 AM

What is the value of the inductance when wound as specified?

Spitso FM Transmitter Sunday, July 19, 2009 10:15:29 AM

Hey guys just finished building this circuit. It does work but is very tempremental. As soon as something comes within 30cm of this circuit it changes the frequency of the transmitter, or as your battery drops its voltage frequency also changes.

anonymous FM Transmitter Tuesday, July 14, 2009 10:48:50 PM

@ Chris Why don't you just learn some of that stuff at least the basics so you can read this. You don't need to know everything related to electronics to make this thing. The only thing you need to know is how to identify the pins of the transistor. that is the only thing that you cannot understand by looking at this diagram. Even then with the the a pc board diagram shown here You don't need to know anything about that. If you google everything you don't understand you would know how to build this in and hour or two. The lines are wires the symbols are different components and some have + - sides like batteries and some don't. You just have to figure out which end is fixed to which wire(basically what goes where) and solder them or use a thing called a breadboard where you just have to plug everything(no soldering). For your information this is a very easy transmitter to make. And if you seriously want to make this I'm sure you'll just Google everything and make one. if you are unsure make a small Led blinking circuit first to get a hang of everything. I repeat its not hard but you have to make an effort. Asking for a better diagram and better explanation for this circuit is like asking for a cab to pic you up near you bed so that you would't have to learn how to walk to the door.

Arifuddin FM Transmitter Wednesday, May 27, 2009 6:16:59 AM

i am going to try this. we can use a fixed capacitor (say 10pf) and we can alter the coil length to get the required frequency. Testing this circuit requires a lot of patience as u have to tune it to know the resulting frequency. I prefer u to use a phone with fm receiver. search for stations and u will probably know your frequency. Hope this will help u a lot. enjoy [:)]

tacal FM Transmitter Friday, April 24, 2009 6:34:57 PM

In what frequency(channel) do this transmitter send information

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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?
Viraj Mehta	FM Transmitter	Thursday, September 03, 2009 7:54:05 AM
I want to know the specifications and uses of all the components used in this circuit. Please anybody send me minute details of the components and their purpose.Also I WANT TO KNOW ABOUT THE 5.6uF CAP. AND POSSIBLY A SUBSTITUTE AS ONE IS NOT AVAILABLE PRESENTLY.SECONDLY I WANT THE DETAILS ABOUT THE WORKING OF THE INDUCTOR COILS.These two are primary objectives and then the rest of the other components. Please somebody ler me know about the components' working and oblige.Thanks.
Bojan Andrejek	FM Transmitter	Saturday, August 22, 2009 11:20:08 AM
May I connect something else than electret microphone? Maybe a plug from computer?
scode	FM Transmitter	Thursday, July 23, 2009 12:45:27 AM
What is the value of the inductance when wound as specified?
Spitso	FM Transmitter	Sunday, July 19, 2009 10:15:29 AM
Hey guys just finished building this circuit. It does work but is very tempremental. As soon as something comes within 30cm of this circuit it changes the frequency of the transmitter, or as your battery drops its voltage frequency also changes.
anonymous	FM Transmitter	Tuesday, July 14, 2009 10:48:50 PM
@ Chris Why don't you just learn some of that stuff at least the basics so you can read this. You don't need to know everything related to electronics to make this thing. The only thing you need to know is how to identify the pins of the transistor. that is the only thing that you cannot understand by looking at this diagram. Even then with the the a pc board diagram shown here You don't need to know anything about that. If you google everything you don't understand you would know how to build this in and hour or two. The lines are wires the symbols are different components and some have + - sides like batteries and some don't. You just have to figure out which end is fixed to which wire(basically what goes where) and solder them or use a thing called a breadboard where you just have to plug everything(no soldering). For your information this is a very easy transmitter to make. And if you seriously want to make this I'm sure you'll just Google everything and make one. if you are unsure make a small Led blinking circuit first to get a hang of everything. I repeat its not hard but you have to make an effort. Asking for a better diagram and better explanation for this circuit is like asking for a cab to pic you up near you bed so that you would't have to learn how to walk to the door.
Arifuddin	FM Transmitter	Wednesday, May 27, 2009 6:16:59 AM
i am going to try this. we can use a fixed capacitor (say 10pf) and we can alter the coil length to get the required frequency. Testing this circuit requires a lot of patience as u have to tune it to know the resulting frequency. I prefer u to use a phone with fm receiver. search for stations and u will probably know your frequency. Hope this will help u a lot. enjoy [:)]
tacal	FM Transmitter	Friday, April 24, 2009 6:34:57 PM
In what frequency(channel) do this transmitter send information