User Guide

After Sales

Technical Documentation

Booster Kit BSH–1

Original, 09/94Page 10

Power Level Control Circuit

The pulse–width modulated control signal TXC is initially fed through a

CMOS buffer D300 before being converted into a d.c. voltage by an RC

filter network comprising R301, R302, C300 and C301. This analogue

signal is fed through rectifier diode V603, and then to the non–inverting

input of a comparator N300. A voltage proportional to the output power is

rectified from the directional coupler (V202) by biased Schottky diode

V201. The rectified voltage is fed through R309 to the inverting input of

the comparator N300. The output signal from this comparator adjusts the

primary stage supply voltage of power hybrid N200 until both inputs of the

comparator have equal voltage levels. This ensures the power control

loop maintains the output power precisely at the desired value.

Transmitter Enable Circuit

The booster receives the transmitter enable command from the incoming

RF signal, which is rectified by Schottky diode pair V200. The rectified

signal is fed to the non–inverting input of a comparator N300. The

inverting input of the comparator has a fixed reference voltage, +4 V, so

when the rectified signal is higher than the reference the output of the

comparator goes high and the transmitter is switched on by transistors

V600 and V601.

Power–off Circuit

The booster unit is also provided with a ’watchdog’ function, which turns

off all supply voltages when a malfunction is detected. Comparator N300

detects the incoming RF signal and comparator N300 detects the output

signal of the booster. Both comparator output signals are fed through

voltage dividers to an EXOR time delay (approx 3s) circuit comprising

R511, C606 gate D300. The D300 output signal is fed via comparator

N400, which forms output TXI which in turn is fed to HFJ.

If TXI goes low, the HJF executes power off, i.e. removes VC. This, in

turn makes mains switch V218 non–conductive ensuring all supply

voltages disappear. When VC is removed, V219 becomes

non–conductive, which in turn makes V501 conduct. V501 discharges

C606 so that restarting the booster is possible when VC is reapplied.

Watchdog Truth Table

Input Detector Output Detector Status TXI

Error