3 Watt FM Transmitter

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Author	Views	Views Today	Rank	Comments
Rae XL Tkacik	228,398	40		77

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

Add A Comment

hitz 3 Watt FM Transmitter Monday, April 29, 2013 5:28:55 AM

This is an awsome transmitter. that i had ever seen in my life with an unbelievable range of 8 miles . thank u very much sir. its amazing!!!!!!!!!!

anonymous 3 Watt FM Transmitter Tuesday, October 30, 2012 7:34:26 PM

What the hell is wrong with all those lazy people? Why can't they just try putting together the circuits themselves instead of having to be spoon-fed the whole building process. Even weirder is, that some of them are claiming to be studying electronics related subjects and needing these circuits for their graduation project. If that's true, than how can't you understand these fairly simple diagrams, and what does that say about the intelligence of students or colleges/universities? It's mind boggling when you think about it.
(Editor's notes: I agree 100%.)

Radio Pirate 3 Watt FM Transmitter Friday, March 02, 2012 10:09:19 PM

Stop begging please. This is an easy schematic, so it shouldn't take you long to create a pcb layout from it. If you can't then you shouldn't start with this project. If you don't know how to make the coils/inductors, go start with a simple transmitter, google for "FM BUG". With these small transmitters yo ucan gain a lot of experience, then you can start with bigger projects. Stop asking about teh range, because the range depends on many factors, how you build the transmitter, your swr, and the quality of the coax etc. All passive components are available on the market, except for the 2N3866 and 2N3553 but you still can buy them from e-bay (watch out for fakes), well some companies still make them but you'll need to find it out yourself, I'm not going to post any links here. If you want any other transistors you need to checkout the datasheets of them and compare them with available transistors. For BF115 you can use a BF199. 7810 is a voltage regulator, you can buy this component it's really cheap (yes even for Indians). Look for 7810 or 78L10, they're available in a TO-92 and a TO-220 package. And people don't forget to use a dummyload when you're configurating the stages and power. If you don't use a dummyload you will burnout the final transistor. For the stability, you need to cool your transistors with good heatsinks, use the proper shielding for every stage, and build a good metal case around your transmitters pcb. The ferroxcube thingy is a simple wide band choke with 6 holes in it. If you don't know what it is google it (image's), you can get this part everywhere. And my final words are; don't use this crappy transmitter for serious businness! Because it will interfere on the whole RF band, it will jam important frequencies (air traffic, emergency etc)! I will build this transmitter this month with a fifteen watt amplifier. Imma going to check this page often.

carristers 3 Watt FM Transmitter Thursday, February 24, 2011 10:14:41 AM

this transmitter with a home made broadcast centre can do wonders.try it with multireplier and communication within 3 miles using a modulated mike in specific radios will do wonders.i made it why not you!

PRAKASH SHARMA 3 Watt FM Transmitter Friday, January 21, 2011 10:56:37 AM

I made it but not working why? plz send me a circuit with easy way.

indx 14 3 Watt FM Transmitter Saturday, November 27, 2010 2:32:42 PM

Well to those who are having trouble, it may help to a) try building an simple(r) FM transmitter (google search) or b) try building an AM transmitter, unless FM is necessary. Also, looking up what each individual component is, and what it's job is in this project may also help. (slightly simpler) ones (for casual learning/fun): http://www.pira.cz/entx1.htm

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

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hitz	3 Watt FM Transmitter	Monday, April 29, 2013 5:28:55 AM
This is an awsome transmitter. that i had ever seen in my life with an unbelievable range of 8 miles . thank u very much sir. its amazing!!!!!!!!!!
anonymous	3 Watt FM Transmitter	Tuesday, October 30, 2012 7:34:26 PM
What the hell is wrong with all those lazy people? Why can't they just try putting together the circuits themselves instead of having to be spoon-fed the whole building process. Even weirder is, that some of them are claiming to be studying electronics related subjects and needing these circuits for their graduation project. If that's true, than how can't you understand these fairly simple diagrams, and what does that say about the intelligence of students or colleges/universities? It's mind boggling when you think about it. (Editor's notes: I agree 100%.)
Radio Pirate	3 Watt FM Transmitter	Friday, March 02, 2012 10:09:19 PM
Stop begging please. This is an easy schematic, so it shouldn't take you long to create a pcb layout from it. If you can't then you shouldn't start with this project. If you don't know how to make the coils/inductors, go start with a simple transmitter, google for "FM BUG". With these small transmitters yo ucan gain a lot of experience, then you can start with bigger projects. Stop asking about teh range, because the range depends on many factors, how you build the transmitter, your swr, and the quality of the coax etc. All passive components are available on the market, except for the 2N3866 and 2N3553 but you still can buy them from e-bay (watch out for fakes), well some companies still make them but you'll need to find it out yourself, I'm not going to post any links here. If you want any other transistors you need to checkout the datasheets of them and compare them with available transistors. For BF115 you can use a BF199. 7810 is a voltage regulator, you can buy this component it's really cheap (yes even for Indians). Look for 7810 or 78L10, they're available in a TO-92 and a TO-220 package. And people don't forget to use a dummyload when you're configurating the stages and power. If you don't use a dummyload you will burnout the final transistor. For the stability, you need to cool your transistors with good heatsinks, use the proper shielding for every stage, and build a good metal case around your transmitters pcb. The ferroxcube thingy is a simple wide band choke with 6 holes in it. If you don't know what it is google it (image's), you can get this part everywhere. And my final words are; don't use this crappy transmitter for serious businness! Because it will interfere on the whole RF band, it will jam important frequencies (air traffic, emergency etc)! I will build this transmitter this month with a fifteen watt amplifier. Imma going to check this page often.
carristers	3 Watt FM Transmitter	Thursday, February 24, 2011 10:14:41 AM
this transmitter with a home made broadcast centre can do wonders.try it with multireplier and communication within 3 miles using a modulated mike in specific radios will do wonders.i made it why not you!
PRAKASH SHARMA	3 Watt FM Transmitter	Friday, January 21, 2011 10:56:37 AM
I made it but not working why? plz send me a circuit with easy way.
indx 14	3 Watt FM Transmitter	Saturday, November 27, 2010 2:32:42 PM
Well to those who are having trouble, it may help to a) try building an simple(r) FM transmitter (google search) or b) try building an AM transmitter, unless FM is necessary. Also, looking up what each individual component is, and what it's job is in this project may also help. (slightly simpler) ones (for casual learning/fun): http://www.pira.cz/entx1.htm
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