This Simple Portable FM transmitter includes a limiter, a microphone amplifier and a PLL digital tuning. All the components are placed on one circuit board. The RF power is switchable between 1 W (HI) and 0,2 W (LO).The schematic diagram is split into 3 parts: RF part (numbered from 1), PLL (numbered from 30) and audio part (numbered from 50). Connect a 6 V / 0,1 A bulb to the output and set the correct frequency on PLL. Set the RF power to HI. currently activate the transmitter. you must tune it on a receiver. perhaps you may stretch coils of the L1. Fix the L1 in position when the tuning voltage (on Q3) is in range 4-9 V. Then use C15, C16 and C17 to regulate the best power (the highest light of the bulb). Then you'll be able to connect antenna and audio signal. change R1 till the audio sounds as loud because the alternative stations.
Technical specifications 1 Watt Portable FM Transmitter
Supply voltage: 12 V from accumulator or regulated power supply
Supply current (HI/LO): 270/170 mA
RF power HI: 1 W
RF power LO: 0,2 W
Impedance: 50-75 ohm
Frequency range: 87,5-108 MHz
Modulation type: wide-band FM
Modulation inputs: line, mic, RDS/MPX
PCB dimensions: 11,3 x 8,8 cm
