3 Watt FM Transmitter


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Rae XL Tkacik 244,711 15 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


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

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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