How to build 3W FM Transmitter

December 2, 2010 - category: 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).

Circuit diagram

3W FM Transmitter-Circuit diagram


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


  • 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.

author: Rae XL Tkacik, vocko@atlas.cz
circuit from http://www.aaroncake.net/circuits/index.asp

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