PLL 1 Watt FM transmitter

Posted on Aug 25, 2012

This small FM transmitter includes a limiter, a microphone amplifier and a PLL digital tuning. All the parts are placed on one circuit board. The RF power is switchable between 1 W (HI) and 0,2 W (LO). Technical specifications: 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.

PLL 1 Watt FM transmitter
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PLL 1 Watt FM transmitter - image 1
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PLL 1 Watt FM transmitter - image 2
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The schematic diagram is divided into three 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 right frequency on PLL. Set the RF power to HI. Now turn on the transmitter. You should tune it on a receiver. Maybe you might 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 adjust the highest power (the highest light of the bulb). Then you can connect antenna and audio signal. Adjust R1 until the audio sounds as loud as the other stations. Complete parts list Resistors: 1x 10 1x 47 1x 100 1x 270 2x 220 3x 470 1x 820 5x 1k 1x 1,5 k 1x 4,7 k 9x 10 k 3x 22 k 3x 27 k 1x 56 k 1x 47 k 1x 180 k 1x 240 k 1x 10 M 3x pot. 5 k log. Capacitors: 1x 8,2 pF 2x 10 pF 3x 22 pF 5x 100 pF 8x 1 nF 1x 1 nF plastic 2x 2,2 nF 5x 10 nF 2x 47 nF 4x 100 nF mini 1x 150 nF 1x 0,47 uF 2x 1 uF 2x 2,2 uF 1x 4,7 uF 4x 10 uF 1x 47 uF 1x 100 uF 1x 220 uF 2x 470 uF 2x 1 uF tantal 1x 10 uF tantal 1x trimmer 47 pF 2x trimmer 60 pF Semiconductors: 1x BC547C (BC548C, BC547B) 1x BFR91A 1x BFR96 1x 2SC1971 1x BC556B 1x BF245C 2x LM386 1x SAA1057 1x PIC16F84A-04 + socket 1x 78L05 1x Yellow LED 3 mm 2x BB109G, BBY31 or BB409 Misc: 1x 4 MHz crystal 2x switch 1x button 1x jumpers 2x8 pins or DIP switches 1x power supply connector...

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