3 Watt FM Transmitter

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).



This is the schematic of the 3W FM Transmitter


Total Qty.
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  



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

  3. 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.

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

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

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

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