Vector-LP Radio Beacon Transmitter Technical Instruction Manual
Page 6-1 (6-2 Blank)
Section 6 Theory of Operation
Issue 1.1
Vector-LP Radio Beacon Transmitter
TECHNICAL INSTRUCTION MANUAL
Section 6
THEORY OF OPERATION
6.1 INTRODUCTION
The theory of operation for the Vector-LP
Radio Beacon transmitter is presented in
this section. Frequent reference is made to
electrical schematics (e.g., Figure SD-1).
They are located in Section 9 of this
manual. Circuits that are shown on
electrical schematics, but not described in
this section are either beyond the scope of
this manual or are not used for NDB
applications.
6.2 TRANSMITTER OVERVIEW
The transmitter operates at one fixed
frequency in the LF/MF band (190 kHz to
535 kHz) or in the MF band (536 kHz to
1200 kHz and 1600 kHz to 1800 kHz). It
provides up to 125 W (VR125) or 250 W
(VR250) of continuous carrier power. It
automatically transmits specific beacon
identification signals at pre-selected
repetition rates. Special codes may also be
transmitted when commanded from an
external source. Provision is made for local
or remote operation of the transmitter as
well as antenna fine-tuning through
controls on the transmitter's front panel. If
the standby option is purchased, provision
is made for automatic changeover from the
selected main side of the transmitter to the
standby side when the selected main side's
critical parameters are not met. The
transmitter operates from a single phase,
47 Hz to 63 Hz ac power supply (170 V to
270 V ac for VR250; 90 V to 270 V for
VR125), using switch mode power
supplies. A 48 V dc input option (and 24 V
dc for VR125 only) can also be
purchased. Emission is continuous carrier
(NON) beacon keyed identification tone
(A2A) and beacon with voice (A2A/A3A).
Local control/monitoring is done using
front panel membrane switches and a
graphic liquid crystal display. Critical
parameters such as forward power,
reflected power and antenna current can
also be displayed on an analog meter on
the front of the transmitter.
Remote control and monitoring can be
provided over several optional interfaces.
The transmitter also has provision to
interface with a Nautel antenna tuning unit
(ATU), using an isolated RS485 serial link.
This ATU link allows the transmitter to
regulate antenna current, and therefore
maintain constant field strength, by auto-
adjusting its output power in accordance
with the ATUs antenna current sample.
The transmitter circuitry can be
represented using four functional stages
(see Figure 6-1):
x
Ac-Dc
Power
Stage
x
Exciter
Stage
x
Control/Monitor
Stage
x
RF
Power
Stage
6.3 AC-DC POWER STAGE
See Figures 6-1 and SD-1. The ac-dc
power stage accepts the ac power source
or optional dc power source and converts it
to the necessary low level dc voltages
required throughout the transmitter. The ac
input voltage is also applied directly to the
RF power stage. The ac-dc power stage’s
primary components are the ac-dc
universal input power supplies (U2 and U3,
if used) and the interface PWB (A11). If the
dc input option is purchased, the
transmitter also includes the dc-dc
universal input power supply (U10) and the
battery boost PWB (A16A1).
