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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MarkH FM Transmitter Wednesday, May 20, 2020 1:04:59 PM

Is this FM transmitter available in kit form with all the part and PWB?

Ahmed FM Transmitter That works Monday, April 03, 2017 7:56:51 PM

Thank you for this great circuit. I've tried it back in 2001 and it's just worked perfect. I've searched for the website and was so glad that it's still up and running. I made a post on my blog and an instructable. http://idea-arabic.blogspot.com.eg/2015/11/fm-transmitter.html

Ashok FM Transmitter Monday, June 30, 2014 12:48:38 AM

Hi! I'd like to use the transmitter for remote switching.How to replace mic to send a switching pulse? I'm a teacher in the high school & I'd like very much to put forward this project for the annual competition for my students. Thank you Sir! Ashok.

Tanyut Reciever Sunday, June 22, 2014 1:57:51 AM

Can you please tell me how to make a reciever of the same frequency as this tranmitter.

Gabberworld FM Transmitter Friday, April 11, 2014 3:58:42 PM

KN2222A looks like the 2N3904, soo i think that yes you can use that

anonymous FM Transmitter Wednesday, April 09, 2014 8:39:08 PM

this transmitter needs stable voltage, any voltage trop or rise changes the frequency

jadexs FM Transmitter Sunday, September 01, 2013 12:59:20 AM

please help me about this circuit,can i replace mic by audio jack ?????

Thinkker FM Transmitter Saturday, July 13, 2013 10:16:02 AM

I builded that transmitter to that PCB layout seen on that page. That little transmitter is very unstable, it drift 89.100 to 89.329, 229khz in 5mins! And FM deviation iss very slow, only about 5khz. So after that I builded smaller versio of that using junk SMD parts and with little modifications. I get it stability to 50khz/5min and deviation to allmost 100khz.

sarah FM Transmitter Monday, October 22, 2012 9:26:10 AM

what is BS170? is this transistor and how this fm transmiter give best result?

anonymous FM Transmitter Sunday, October 21, 2012 11:09:32 PM

How were the values of the FM transmitter determined?

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MarkH	FM Transmitter	Wednesday, May 20, 2020 1:04:59 PM
Is this FM transmitter available in kit form with all the part and PWB?
Ahmed	FM Transmitter That works	Monday, April 03, 2017 7:56:51 PM
Thank you for this great circuit. I've tried it back in 2001 and it's just worked perfect. I've searched for the website and was so glad that it's still up and running. I made a post on my blog and an instructable. http://idea-arabic.blogspot.com.eg/2015/11/fm-transmitter.html
Ashok	FM Transmitter	Monday, June 30, 2014 12:48:38 AM
Hi! I'd like to use the transmitter for remote switching.How to replace mic to send a switching pulse? I'm a teacher in the high school & I'd like very much to put forward this project for the annual competition for my students. Thank you Sir! Ashok.
Tanyut	Reciever	Sunday, June 22, 2014 1:57:51 AM
Can you please tell me how to make a reciever of the same frequency as this tranmitter.
Gabberworld	FM Transmitter	Friday, April 11, 2014 3:58:42 PM
KN2222A looks like the 2N3904, soo i think that yes you can use that
anonymous	FM Transmitter	Wednesday, April 09, 2014 8:39:08 PM
this transmitter needs stable voltage, any voltage trop or rise changes the frequency
jadexs	FM Transmitter	Sunday, September 01, 2013 12:59:20 AM
please help me about this circuit,can i replace mic by audio jack ?????
Thinkker	FM Transmitter	Saturday, July 13, 2013 10:16:02 AM
I builded that transmitter to that PCB layout seen on that page. That little transmitter is very unstable, it drift 89.100 to 89.329, 229khz in 5mins! And FM deviation iss very slow, only about 5khz. So after that I builded smaller versio of that using junk SMD parts and with little modifications. I get it stability to 50khz/5min and deviation to allmost 100khz.
sarah	FM Transmitter	Monday, October 22, 2012 9:26:10 AM
what is BS170? is this transistor and how this fm transmiter give best result?
anonymous	FM Transmitter	Sunday, October 21, 2012 11:09:32 PM
How were the values of the FM transmitter determined?