400mW VCO FM Transmitter

This simple 400mW transmitter broadcasts audio on 87.5 - 108 MHz FM radio band. With good dipole antenna transmission range up to 4km is possible.

Step 1: 400mW VCO FM Transmitter

This simple 400mW transmitter broadcasts audio on 87.5 - 108 MHz FM radio band. With good dipole antenna transmission range up to 4km is possible. Frequency is selected by adjusting R1 potentiometer. Transmitter should be powered by regulated 12-14V power supply with at least 100mA current rating.


400mW VCO FM Transmitter 

Parts list 

Capacitors: 
C1, C2, C12 - 100 pF (ceramic) 
C3, C5 - 0,22 uF (electrolytic) 
C4 - 1,8 nF (plastic) 
C13, C16, C17, C19 - 1 nF (ceramic) 
C8, C9 - 10 pF (ceramic) 
C10 - 47 pF (ceramic) 
C11 - 8,2 pF (ceramic) 
C14 - 60 pF trimmer 
C15 - 35 pF trimmer 
C18, C7 - 100 nF (ceramic) 
C20 - 470 uF (electrolytic, 16 V) 

Coils: 
(All coils are free-standing air-core types, wound of 0,7 mm Cu wire, 6 mm internal diameter.) 
L1 - 4,5 coils 
L2 - 9,5 coils 
L3 - 4,5 coils 

Resistors: 
R1, R2 - 10 k pot. 
R3 - 33 k 
R4, R7, R12 - 10 k 
R5, R11 - 470 
R6 - 27 k 
R8 - 22 k 
R9 - 270 
R10 - 100 

Misc.: 
D1 - BB409 (MV2109, MV209, BB109G, BBY31) varicap 
T1 - BC547C (2SC9018, BC548C, BC547B) 
T2 - BFR91A (2SC3355, BFR96) 
T3 - BFR96 (2N4427, 2N3866) 

Antenna 
Power supply 
3,5 mm jack 
CD player, computer 
6 V / 0,1 A bulb 

Tuning 
Connect the 6 V / 0,1 A bulb to the output and use R1 to tune the right frequency. Maybe you might stretch coils of the L1. Then use C14 and C15 to adjust the highest power (the highest light of the bulb). Then you can connect antenna and audio signal. Adjust R2 until the audio sounds as loud as the other stations.


400mW VCO FM Transmitter


400mW VCO FM Transmitter


400mW VCO FM Transmitter

 

 

Oct 21,2015
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