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.
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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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