This is the diagram of the transmitter, the connectors CN1 and CN2 are stereo audio inputs of the trimpot (pots can be added) are for the volume adjustment capacitor + resistor (R1 / C4 and C11 / R2) form the pre-emphasis filter in the case of Brazil is 75μS.
The crystal ensures 38KHz stereo broadcast, in case you do not find this component to the assembly of your circuit, you will have a mono high-quality transmission, the MPX signal (with 2 audio channels multiplexed), leave the pin 14 and join with the 19kHz pilot signal (pin 13) and return to ci on pin 12 and will take the stage high-frequency oscillator formed on pins 9 and 10, the coil of 3.5 turns of the type found in FM radios in parallel with the 10pF capacitor C13 will be responsible for the fluctuation in the FM band.
The following high-frequency signal of the transistor T1 pin 7 to ensure a greater distance n transmission, the antenna coupling capacitor C9 which may be a telescopic or a piece of stiff wire.
The power supply should be a battery 9Volts preferably rechargeable 9-volt feed to the power transistor, as BA for the integrated circuit 1404 is required only 3 volts or it can burn. then 3 1N4148 diodes are used as a reference voltage of 2.1 volts in this source.
When assembling this circuit, make sure all components are positioned in the correct place and then connect the battery, then connect an audio source such as an MP4 and a nearby FM receiver, adjust the coil, using a little key plastic or wood, until you hear the signal on the radio. If you can not try to set other values for C13, and without then redo the settings.
Parts for Stereo FM Transmitter with BA1404
Resistors 1/8 Watt 5%
R1, R2 47K Yellow, Violet, Orange, Gold
R3, R7 270 Red, Violet, Brown, Gold
R4 10K Brown, Black, Orange, Gold
R5 4.7K Yellow, Violet, Red, Gold
R6 150K Brown, Green, Yellow, Gold
R8, R9 22K Red, Red, Orange, Gold
R10 470 Yellow, Violet, Brown, Gold
C1, C5, C10, C12 10΅F/16V Polarized Electrolytic Capacitor
C2,C4, C7, C9, C11, C15, C17 1nF 25V Ceramic Capacitor
C3, C6, C8, C13, C14 10pF 25V Ceramic Capacitor
C16 470΅F/16V Polarized Electrolytic Capacitor
IC1 BA1404 FM stereo transmitter chip
T1 2SC2458 RF Transistor
D1, D2, D3 1N4148 Diode
L1 3.5 turns coil with adjustable core
P1, P2 1k Trimpot Volume Adjustment
ANT Connect telescopic antenna or piece of stiff wire
B1 9V battery
CN1 Left audio connector
CN2 Right audio connector
X1 38KHz quartz crystal
Solder, wire, printed circuit board, box, connectors, etc..
BA1404 HI-FI Stereo FM Transmitter Kit