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

This is the schematic of the FM Transmitter

PC Board Layout and Parts Placement

This is the printed circuit layout and parts placement of the FM Transmitter

Parts

Part
Total Qty.
Description
Substitutions
C110.001uf Disc Capacitor
C215.6pf Disc Capacitor
C3,C4210uf Electrolytic Capacitor
C513-18pf Adjustable Cap
R11270 Ohm 1/8W Resistor270 Ohm 1/4W Resistor
R2,R5,R634.7k 1/8W Resistor4.7K 1/4W Resistor
R3110k 1/8W Resistor10K 1/4W Resistor
R41100k 1/8W Resistor100K 1/4W Resistor
Q1, Q222N2222A NPN Transistor2N3904, NTE123A
L1, L225 Turn Air Core Coil
MIC1Electret Microphone
MISC19V Battery Snap, PC Board, Wire For Antenna

Notes

  1. 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.
  2. C5 is used for tuning. This transmitter operates on the normal broadcast frequencies (88-108MHz).
  3. Q1 and Q2 can also be 2N3904 or something similar.
  4. You can use 1/4 W resistors mounted vertically instead of 1/8 W resistors.
  5. You may want to bypass the battery with a .01uf capacitor.
  6. An antenna may not be required for operation.
  7. 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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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?
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?
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