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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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?

anonymous FM Transmitter Saturday, September 15, 2012 6:33:50 PM

Hello friends i maid this Fm transmitter successfully . you can get the all details from this link

chano 28 awg enamel Saturday, September 01, 2012 7:38:15 PM

where can i buy a meter of 28 awg enamel coated wire?

anonymous FM Transmitter Friday, June 22, 2012 7:46:56 AM

Very very good. I want to create a walkie-talkie

Gabberworld FM Transmitter Wednesday, June 20, 2012 4:13:16 PM

yes, audio input add to the c3, remove the r5, q2, r4, c4, r6 and mic, as they not needed then

jorge sales FM Transmitter Sunday, June 10, 2012 12:20:03 PM

Can I replace the mic with an audio jack so that I can put an audio input via mp3 player etc. to the transmitter instead? Thank you!

Jitendranepali FM Transmitter Tuesday, May 29, 2012 6:24:33 AM

Can I use KN2222A transistor instead of 2N2222A . Tell me fast...waiting

Gabberworld FM Transmitter Thursday, May 10, 2012 11:40:33 AM

i tried transistor 2N3904 for Q1 and it works, after testing and testing the 2N3904 i found that using BS170 gives better signal results.

Rob FM Transmitter Thursday, May 03, 2012 2:41:30 PM

Why make one, when you can buy one. I purchased this one http://wholehousefmtransmitter.com and it seems to work all right. Deal with some cracking every once in awhile but it does ok.

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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?
anonymous	FM Transmitter	Saturday, September 15, 2012 6:33:50 PM
Hello friends i maid this Fm transmitter successfully . you can get the all details from this link
chano	28 awg enamel	Saturday, September 01, 2012 7:38:15 PM
where can i buy a meter of 28 awg enamel coated wire?
anonymous	FM Transmitter	Friday, June 22, 2012 7:46:56 AM
Very very good. I want to create a walkie-talkie
Gabberworld	FM Transmitter	Wednesday, June 20, 2012 4:13:16 PM
yes, audio input add to the c3, remove the r5, q2, r4, c4, r6 and mic, as they not needed then
jorge sales	FM Transmitter	Sunday, June 10, 2012 12:20:03 PM
Can I replace the mic with an audio jack so that I can put an audio input via mp3 player etc. to the transmitter instead? Thank you!
Jitendranepali	FM Transmitter	Tuesday, May 29, 2012 6:24:33 AM
Can I use KN2222A transistor instead of 2N2222A . Tell me fast...waiting
Gabberworld	FM Transmitter	Thursday, May 10, 2012 11:40:33 AM
i tried transistor 2N3904 for Q1 and it works, after testing and testing the 2N3904 i found that using BS170 gives better signal results.
Rob	FM Transmitter	Thursday, May 03, 2012 2:41:30 PM
Why make one, when you can buy one. I purchased this one http://wholehousefmtransmitter.com and it seems to work all right. Deal with some cracking every once in awhile but it does ok.