3 Watt FM Transmitter

Author	Views	Views Today	Rank	Comments
Rae XL Tkacik	144,184	92		71

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

Parts

Part	Total Qty.	Description	Substitutions
R1,R4,R14,R15	4	10K 1/4W Resistor
R2,R3	2	22K 1/4W Resistor
R5,R13	2	3.9K 1/4W Resistor
R6,R11	2	680 Ohm 1/4W Resistor
R7	1	150 Ohm 1/4W Resistor
R8,R12	2	100 Ohm 1/4W Resistor
R9	1	68 Ohm 1/4W Resistor
R10	1	6.8K 1/4W Resistor
C1	1	4.7pF Ceramic Disc Capacitor
C2,C3,C4,C5,C7,C11,C12	7	100nF Ceramic Disc Capacitor
C6,C9,C10	3	10nF Ceramic Disc Capacitor
C8,C14	2	60pF Trimmer Capacitor
C13	1	82pF Ceramic Disc Capacitor
C15	1	27pF Ceramic Disc Capacitor
C16	1	22pF Ceramic Disc Capacitor
C17	1	10uF 25V Electrolytic Capacitor
C18	1	33pF Ceramic Disc Capacitor
C19	1	18pF Ceramic Disc Capacitor
C20	1	12pF Ceramic Disc Capacitor
C21,C22,C23,C24	4	40pF Trimmer Capacitor
C25	1	5pF Ceramic Disc Capacitor
L1	1	5 WDG, Dia 6 mm, 1 mm CuAg, Space 1 mm
L2,L3,L5,L7,L9	5	6-hole Ferroxcube Wide band HF Choke (5 WDG)
L4,L6,L8	3	1.5 WDG, Dia 6 mm, 1 mm CuAg, Space 1 mm
L10	1	8 WDG, Dia 5 mm, 1 mm CuAg, Space 1 mm
D1	1	BB405	BB102 or equal (most varicaps with C = 2-20 pF [approx.] will do)
Q1	1	2N3866
Q2,Q4	2	2N2219A
Q3	1	BF115
Q5	1	2N3553
U1	1	7810 Regulator
MIC	1	Electret Microphone
MISC	1	PC Board, Wire For Antenna, Heatsinks

Notes

Email Rae XL Tkacik with questions, comments, etc.

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.

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

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

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

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anonymous 3 Watt FM Transmitter Wednesday, April 14, 2010 4:03:51 PM

Have any questions been answered yet? This is a test question to see if any one monitoring this site. What happens if I poop on the transmitter?
(Editor's notes: Questions aren't answer here, hence why these are called "Comments". If you want your question answers, post to the forum as it says above the comments section.)

darren 3 Watt FM Transmitter Monday, April 05, 2010 9:39:49 AM

the transmitter design is just basic. it will give 3-4 watts with the output device with ease. but the oscillator is not pll so it may not be stable in frequency operation. add a pll (phase locked loop) to the oscillator and youre on to a good start. my design that i made uses a similar layout and i added a pll to it and its now giving out about 7 watts into 50ohms.

KXRN 93.5 3 Watt FM Transmitter Friday, April 02, 2010 6:34:30 PM

We are a licensed LP FM radio station that has to duce our max output of 100 watts down to 50 watts because of our proximity (Within 100 miles) to the California/Mexico border.. ok now that we establish a transmitter site we are required to reduce our 50 watts down to 3 watts because of the position on top of a hill, otherwise known as the line of sight over the community. Is it worth it to have an LPFM in my community if i cant get maximum coverage or wattage..?

anonymous 3 Watt FM Transmitter Thursday, September 10, 2009 1:59:38 PM

A semi-professional stereo coder to complete this transmitter can be found at http://homepage.univie.ac.at/johann.doblhofer/sender/sesmanl.html although the description is in German

anonymous 3 Watt FM Transmitter Friday, July 24, 2009 10:48:30 AM

Will using a longer antenner provide greater range.?

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

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anonymous	3 Watt FM Transmitter	Wednesday, April 14, 2010 4:03:51 PM
Have any questions been answered yet? This is a test question to see if any one monitoring this site. What happens if I poop on the transmitter? (Editor's notes: Questions aren't answer here, hence why these are called "Comments". If you want your question answers, post to the forum as it says above the comments section.)
darren	3 Watt FM Transmitter	Monday, April 05, 2010 9:39:49 AM
the transmitter design is just basic. it will give 3-4 watts with the output device with ease. but the oscillator is not pll so it may not be stable in frequency operation. add a pll (phase locked loop) to the oscillator and youre on to a good start. my design that i made uses a similar layout and i added a pll to it and its now giving out about 7 watts into 50ohms.
KXRN 93.5	3 Watt FM Transmitter	Friday, April 02, 2010 6:34:30 PM
We are a licensed LP FM radio station that has to duce our max output of 100 watts down to 50 watts because of our proximity (Within 100 miles) to the California/Mexico border.. ok now that we establish a transmitter site we are required to reduce our 50 watts down to 3 watts because of the position on top of a hill, otherwise known as the line of sight over the community. Is it worth it to have an LPFM in my community if i cant get maximum coverage or wattage..?
anonymous	3 Watt FM Transmitter	Thursday, September 10, 2009 1:59:38 PM
A semi-professional stereo coder to complete this transmitter can be found at http://homepage.univie.ac.at/johann.doblhofer/sender/sesmanl.html although the description is in German
anonymous	3 Watt FM Transmitter	Friday, July 24, 2009 10:48:30 AM
Will using a longer antenner provide greater range.?
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