3 Watt FM Transmitter

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Rae XL Tkacik 94,254 77 66
This is the schematic for an FM transmitter with 3 to 3.5 W output power that can be used between 90 and 110 MHz. Although the stability isn't so bad, a PLL can be used on this circuit.

This is a circuit that I've build a few years ago for a friend, who used it in combination with the BLY88 amplifier to obtain 20 W output power. From the notes that I made at the original schematic, it worked fine with a SWR of 1 : 1.05 (quite normal at my place with my antenna).

Schematic

This is the schematic of the 3W FM Transmitter

Parts
Part
Total Qty.
Description
Substitutions
R1,R4,R14,R15410K 1/4W Resistor
R2,R3222K 1/4W Resistor
R5,R1323.9K 1/4W Resistor
R6,R112680 Ohm 1/4W Resistor
R71150 Ohm 1/4W Resistor
R8,R122100 Ohm 1/4W Resistor
R9168 Ohm 1/4W Resistor
R1016.8K 1/4W Resistor
C114.7pF Ceramic Disc Capacitor
C2,C3,C4,C5,C7,C11,C127100nF Ceramic Disc Capacitor
C6,C9,C10310nF Ceramic Disc Capacitor
C8,C14260pF Trimmer Capacitor
C13182pF Ceramic Disc Capacitor
C15127pF Ceramic Disc Capacitor
C16122pF Ceramic Disc Capacitor
C17110uF 25V Electrolytic Capacitor
C18133pF Ceramic Disc Capacitor
C19118pF Ceramic Disc Capacitor
C20112pF Ceramic Disc Capacitor
C21,C22,C23,C24440pF Trimmer Capacitor
C2515pF Ceramic Disc Capacitor
L115 WDG, Dia 6 mm, 1 mm CuAg, Space 1 mm
L2,L3,L5,L7,L956-hole Ferroxcube Wide band HF Choke (5 WDG)
L4,L6,L831.5 WDG, Dia 6 mm, 1 mm CuAg, Space 1 mm
L1018 WDG, Dia 5 mm, 1 mm CuAg, Space 1 mm
D11BB405BB102 or equal (most varicaps with C = 2-20 pF [approx.] will do)
Q112N3866
Q2,Q422N2219A
Q31BF115
Q512N3553
U117810 Regulator
MIC1Electret Microphone
MISC1PC Board, Wire For Antenna, Heatsinks

Notes

  1. Email Rae XL Tkacik with questions, comments, etc.

  2. The circuit has been tested on a normal RF-testing breadboard (with one side copper). Make some connections between the two sides. Build the transmitter in a RF-proof casing, use good connectors and cable, make a shielding between the different stages, and be aware of all the other RF rules of building.

  3. Q1 and Q5 should be cooled with a heat sink. The case-pin of Q4 should be grounded.

  4. C24 is for the frequency adjustment. The other trimmers must be adjusted to maximum output power with minimum SWR and input current.

  5. Local laws in some states, provinces or countries may prohibit the operation of this transmitter. Check with the local authorities.

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Comments

Cthulhu
3 Watt FM Transmitter
Sunday, May 10, 2009 12:12:14 AM
Hey, cool it boy; it just so happens that there are a few of us out here who are not conversant with all the jargon of electronics! Perhaps if you should explain just what the items named actually are, we would all be a lot happier, especially the fellow who is asking! An inductor, for example, is a wire coil, wound according to a certain criteria, and soldered into place. Now you have a go!
Anon
3 Watt FM Transmitter
Wednesday, February 04, 2009 3:45:05 PM
You're a jerk. People like you make our planet a nasty place to live.
anonymous
3 Watt FM Transmitter
Sunday, November 02, 2008 2:15:58 PM
WTF??? If you don't know what a regulator is, or how to make an inductor, or how to work out how far a 3watt transmitter will propergate then you SHOULDN'T BE TRYING TO BUILD ONE!!! Try simpler things fist, like water alarms. Then move on to FM transmitter kits (google search that). You definately shouldn't be worrying about 20/30/50/100watt outputs yet. Besides, this ciruit is non PLL (free running), high power ios completely pointless!! The frequency will be all over the place!! Don't keep embarrasing yourselves with silly questions, DO YOUR RESEARCH!!
DIGME ROBERT
3 Watt FM Transmitter
Monday, October 06, 2008 12:03:40 PM
Well I would like to build this transmitter my self but I dont know how far it is going to cover, it also seems it will be transmitting MONO. Is there a way I can go about it to make it STEREO. Please let me know, and weather I can change the Watts and also what about the frequency? is it adjustable. Thank you
slim
3 Watt FM Transmitter
Monday, August 11, 2008 5:31:02 PM
i wanna run a radio station w/ at least 1 mile distance just want to open up the box plug it in and start i been resarchin on buildin one but i cant get a hold all those electronics where can i buy a package to start my underground radio station or a list of where i can find one sutibule for my needs i can put it together thats not a prob. can u help
francisco
3 Watt FM Transmitter
Wednesday, July 30, 2008 2:30:22 PM
please ! could you explain me more about 8 WDG, Dia 5 mm, 1 mm CuAg, Space 1 mm and how could I mount the coil in pracitce Vy Kindest Rgrds francisco
ehsan
3 Watt FM Transmitter
Saturday, June 21, 2008 4:12:44 PM
What is the u1?
Mansoor
3 Watt FM Transmitter
Thursday, June 19, 2008 11:28:45 PM
Can I make it a 30 watt-100watt by connecting its output to amplifier then to antena,or somehow?? Can I use my remote controlled car,wireless headphones, old radio or somehow just take out a receiver out of something and alter it to work for me. I need to run a radio station for atleast 1miles radius.
freab demissie
fm trasmitter that covers 1km square
Monday, March 17, 2008 8:59:12 AM
it helps me to the final project .so that i want schematic diagram and discription of each components and ratings.
Dumidan
3 Watt FM Transmitter
Tuesday, March 11, 2008 4:44:29 AM
U1 7810 = LM 7810 or equivalent voltage regulator, out=10V
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