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

tushar apa
FM Transmitter
Monday, May 12, 2008 6:12:21 AM
this circuit is very easy
RanjanLama
FM Transmitter
Monday, May 05, 2008 8:00:10 AM
Hi I making fm transmitter but didn't success. Pls. can anyone help me to provide with working schematic diagram of FM transmitter. would be greatful if you also provide all detail calculation and comments on it. cheers
prakash chand
FM Transmitter
Sunday, May 04, 2008 9:29:28 AM
how to make a fm transmitter with a 5 km range and a also a highly sensitive fm receiver.
bitzero
FM Transmitter
Saturday, May 03, 2008 10:14:36 AM
has anyone measured frequency response and signal to noise ratio? i plan to put this in my car with my laptop since we have no good radio stations in the mississippi delta!
hussein
FM Transmitter
Wednesday, April 30, 2008 12:18:58 PM
i want to know if an FM receiver receives the signal it can be generate electricity with some special Hardware .??
Michael Muller
FM Transmitter
Tuesday, April 15, 2008 2:46:56 PM
How far will a 10watt FM transmitter broadcast, assuming a good antennae? What's the radius, or range? 5 miles? We are fundraising for a LPFM station and may use this circuit for our transmitter until we have the cash to buy a new, more robust transmitter.
biswojit nayak
FM Transmitter
Tuesday, April 15, 2008 2:38:03 PM
how to make a fm transmitter with a 5 km range and a also a highly sensitive fm receiver. also pl send me the substitutions for the coil of th trans.plz give some theoryticaly and practicaly dacument about fm transmitter..
Mike
FM Transmitter
Tuesday, April 08, 2008 11:41:18 PM
Does anyone know if you can run this transmitter from your computer, transmitting the signal of what ever is playing on windows media player, if so how would you do this?
eno00wen
FM Transmitter
Friday, April 04, 2008 5:53:02 PM
what do the wire coils do exactly are they acting as inductors? do they have anything to do with getting the the dc voltage to oscillate?
SamTechnologies
FM Transmitter
Tuesday, March 18, 2008 2:38:21 PM
The transmitters is a very basic one U can increae the signal strenth a little by increasing the capacitor betwheen emitter & collector of the filnal RF transistor up to about 22pf.Try it & u will see the differece.
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