Here’s a PLL Synthesizer circuit is based on SA1057 and PIC16F84 that converts any existing FM Transmitter into stable rock-solid PLL transmitter. Frequency is selected through 8-DIP switch. PLL Synthesizer board will also require a 100K resistor and varicap diode such as MV2105 or MV2109 to control the frequency of the transmitter’s oscillator.

Features

• Power supply: 8-15 V stabilized, 40 mA
• Frequency range: 82,5-108 MHz
• Step frequency: 100 kHz
• RF input voltage range: 10-500 mV
• RF input impedance: 135 ohm

PLL Synthesizer Schematic Diagram

Pin meaning:
1 – Tuning voltage (output)
3 – RF signal from oscillator (input)
2, 4 – Ground
Tl1 – Reset

Download : Parts Lists – PLL Frequency DIP Switch – User Friendly Program

Software for the IC2:
pll16f84.asm – pll16f84.hex. Oscillator type: RC, watchdog: ON.

Instructions
The Tl1 button resets the unit. Press it after frequency set. The unit provides a reset on power-up, so you don’t need to use the button.
The D1 LED indicates the tuning cycle is done (after one second from reset). It’s not needed to use it and the R6 resistor.
The R8 resistor provides a minimal voltage of about 2 V on the PLL output. Use this resistor if the transmitter’s oscillator doesn’t work if the tunning voltage is below this value (mainly after power-up). Place the resistor over the R3.

Notes
Output of the PLL should not be directly loaded with big capacities (over about 0,3 uF). The PLL loop may be unstable. This applies to some unknown transmitters.

Printed Circuit Board (PCB)

Source : PLL-Digital Tuning

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