PLL tuning module

Phase-locked loop tuning module

The SAA1057 dual-speed phase-locked loop is designed for broadband FM transmitters.

Technical Specifications:

Power supply: 8-15 V regulated, 40 mA

Frequency range: 82.5-108 MHz

Step frequency: 100 kHz

RF input voltage range: 10-500 mV

RF input impedance: 135 ohms

Schematic diagram:

pll.gif (9420 bytes)

Pin meanings:

1 - Tuning Voltage (Output)

3 - Radio frequency signal (input) from the oscillator

2, 4 - Earth

Tl1 - Reset

Parts list:

Capacitor:

C1, C12 - 2.2 nF (ceramic)

C2, C9 - 10 nF (ceramic)

C3 - 47 uF (electrolysis)

C4 - 10 uF (tantalum)

C5 - 0.47 uF (electrolysis)

C6, C11 - 100 nF (ceramic)

C7 - 1 nF (Ceramic)

C8 - 220 uF (electrolysis)

C10 - 22 pF (ceramic)

Resistor:

R1 - 1k

R2 - 4.7k

R3, R4, R5, R7 - 10k

R6 - 1k (optional)

R8 - 47k (optional, see below)

other:

IC1 - SAA1057

IC2 - PIC16F84 (programmed) + socket

IC3 - 78L05

X1 - 4 MHz crystal

D1 - LED diode (optional)

Tl1 - Button (optional)

Jumper or DIP switch

IC2's software:

pll16f84.asm, pll16f84.hex. Oscillator type: RC, Watchdog: On.

Jumper/DIP switch settings: See pllfreq.txt or download the user-friendly program!

illustrate

Tl1 Button Reset Unit. Press it after setting the frequency. The unit provides a reset when the power is on, so you do not need to use this button.

LED D1 indicates that the tuning cycle is complete (one second after reset). It and resistor R6 are not required.

Resistor R8 provides a minimum voltage of approximately 2V to the PLL output. Use this resistor if the transmitter oscillator does not function when the tuning voltage is below this value (primarily after power-on). Place the resistor across R3.

Precautions:

The PLL output should not be directly loaded with a large capacitor (more than approximately 0.3 uF). The PLL loop may be unstable. This applies to some unknown transmitters.

PCB layout

PR = Line Bridge