PLL Tuning Module

PLL Tuning Module


PLL Tuning Module


SAA1057 Dual-speed PLL designed for wideband FM transmitter.

PLL Tuning Module

Technical specifications:

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

Schematic diagram:

pll.gif (9420 bytes)

Pin meaning:

1 – tuning voltage (output)

3 – RF signal from oscillator (input)

2, 4 – ground

Tl1 – reset

Parts list:


C1, C12 – 2,2 nF (ceramic)

C2, C9 – 10 nF (ceramic)

C3 – 47 uF (electrolytic)

C4 – 10 uF (tantalum)

C5 – 0,47 uF (electrolytic)

C6, C11 – 100 nF (ceramic)

C7 – 1 nF (ceramic)

C8 – 220 uF (electrolytic)

C10 – 22 pF (ceramic)


R1 – 1k

R2 – 4k7

R3, R4, R5, R7 – 10k

R6 – 1k (optional)

R8 – 47k (optional, see below)


IC1 – SAA1057

IC2 – PIC16F84 (programmed) + socket

IC3 – 78L05

X1 – 4 MHz crystal

D1 – LED diode (optional)

Tl1 – button (optional)

jumpers or DIP switches

Software for the IC2:

pll16f84.asm, pll16f84.hex. Oscillator type: RC, watchdog: ON.

Jumpers/DIP switches setting: see pllfreq.txt or download user-friendly program!


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.


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.

PCB layout

plldps1.gif (6743 bytes)

PR = wire-bridge

PLL Tuning Module

PLL Tuning Module

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