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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.
it works fine with a SWR of 1 : 1.05. 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.
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Component
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Value
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Component
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Value
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R1,R4,R14,R15
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10K 1/4W
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C18
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33pF Ceramic Disc
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R2,R3
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22K 1/4W
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C19
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18pF Ceramic Disc
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R5,R13
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3.9K 1/4W
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C20
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12pF Ceramic Disc
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R6,R11
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680R 1/4W
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C21,C22,C23,C24
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40pF Trimmer
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R7
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150R 1/4W
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C25
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5pF Ceramic Disc
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R8,R12
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100R 1/4W
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L1
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5 WDG, Dia 6 mm, 1 mm CuAg, Space 1 mm
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R9
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68R 1/4W
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L2,L3,L5,L7,L9
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6-hole Ferroxcube Wide band HF Choke (5 WDG)
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R10
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6.8K 1/4W
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L4,L6,L8
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1.5 WDG, Dia 6 mm, 1 mm CuAg, Space 1 mm
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C1
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4.7pF Ceramic Disc
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L10
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8 WDG, Dia 5 mm, 1 mm CuAg, Space 1 mm
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C2,C3,C4,C5,C7,C11,C12
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100nF Ceramic Disc
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D1
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BB405, BB102 or equal (most varicaps with C = 2-20 pF [approx.] will do)
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C6,C9,C10
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10nF Ceramic Disc
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Q1
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2N3866
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C8,C14
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60pF Trimmer
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Q2,Q4
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2N2219A
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C13
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82pF Ceramic Disc
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Q3
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BF115
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C15
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27pF Ceramic Disc
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Q5
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2N3553
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C16
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22pF Ceramic Disc
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U1
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7810
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C17
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10uF 25V Electrolytic
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MISC
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PC Board, Wire For Antenna, Heatsinks
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Note : Local
laws in some states, provinces or countries may prohibit the operation of this transmitter. Check with the local
authorities
Reference : Aaroncake
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Last
Updated : February 15, 2002