Circuit Operation; Introduction; Rf Circuitry - Tait T889 Manual

M889-00
2.1

Introduction

Power
Vsupply
Control
Q16
4W
RF In
Pad Q1
The T889 comprises a three stage RF power amplifier with extensive control circuitry.
The final stage is composed of four transistors (Q3, Q4, Q5 & Q6) whose outputs are
combined to provide the rated output power.
The configuration of each of the main circuit blocks may be seen on a functional level in
Figure 2.1.
2.2

RF Circuitry

The driver stage of the T889 consists of a two stage transistor amplifier (Q1, Q2) which
delivers a minimum of 40W. This signal is split via three 3dB couplers (L13, L14 & L15)
and used to drive the four final amplifiers (Q3, Q4, Q5 & Q6). These outputs are recom-
bined by L40, L41 & L42 and passed to the antenna socket via the directional coupler
and low pass filter.
The directional coupler senses forward and reflected power, which is rectified (D1, D2)
and passed to the control circuitry for metering, alarm and power control purposes.
Power control is via a series pass transistor (Q16), which controls the supply voltage on
the collector of the driver transistor (Q1).
Copyright TEL
L13
40W
L14
Q2
L15
Figure 2.1 High Level Block Diagram

Circuit Operation

30W
Q3
60W
L40
Q4
120W
30W
L41
30W
Q5
L42
60W
Q6
30W
2.3
100W
RF Out
LPF
Directional
Coupler
02/10/95