Page 6-20
Vector-LP Radio Beacon Transmitter Technical Instruction Manual
Issue 1.1
Section 6 Theory of Operation
6.5.2.6.3 Audio Limiting
U10:B, U10:C, U10:D, Q7, and their
associated components form the audio
limiter. The limiter will raise an alarm at
U10:13 when the audio signal goes above a
pre-defined threshold. It will then compress
the audio signal by adjusting the resistance
across the JFET Q7. This is accomplished by
adjusting the JFET’s base voltage at the
output of the comparators U10:B and U10:C.
6.5.2.7 Audio Monitor
U1:B and T1 condition the forward power
sample signal to produce an audio monitor
signal that can be used to view the modulated
signal being output by the transmitter.
6.5.3 Front Panel Metering
The front panel of the exciter control/monitor
assembly provides local controls and a
graphic user interface to display operating
status, root cause fault detection, RF power,
and critical dc voltage/current levels. The
controller/display PWB is mounted on the
rear of the panel. The front panel is divided
into three sections – system diagram,
diagnostic display and control.
6.5.3.1 SYSTEM DIAGRAM
The system diagram is a functional flow
diagram of the transmitter. Each section of
the flow diagram contains an alarm lamp,
which turns on when a fault occurs in that
section. If a lamp is flashing, the transmitter
has entered a cutback (reduced power) mode
of operation. The lamp that is flashing is likely
the cause for the cutback.
6.5.3.2 DIAGNOSTIC DISPLAY
The diagnostic display is a graphic user
interface (GUI) screen that is navigated using
five associated soft-keys. The majority of the
transmitter’s local control (exciter selection,
power level, etc.) and monitoring (critical
parameter levels, alarm events, etc.) may be
performed from menus on this display. An
analog meter is provided, which can display
forward power, reflected power, modulation
percentage or antenna current.
6.5.3.3 CONTROL SWITCHES
The control switches determine the
transmitter’s control location (local or remote)
and its RF status (on or off).
6.5.3.3.1 Local/Remote Selection
When
Local
is selected, all remote control
functions, except RF off, are disabled and
have no influence on the transmitter's
operating status or pre-set RF power levels.
When
Remote
is selected, all front panel
control functions, except
RF Off
, are disabled
and have no influence on the transmitter's
operating status or pre-set RF power levels.
6.5.3.3.2 RF On/RF Off Selection
When
RF On
is selected (enabled in
Local
mode only), the transmitter’s RF power stage
is enabled to provide an RF output. When
RF
Off
is selected (enabled in
Local
and
Remote
modes), the transmitter’s RF power
stage is inhibited.
6.5.3.3.3 Power Increase/Decrease
When
Power Increase
is pressed (enabled in
Local
mode only), the transmitter’s RF output
power is increased. When
Power Decrease
is pressed (enabled in
Local
mode only), the
transmitter’s RF output power is decreased.
Additionally, if both the
Power Increase
and
Power Decrease
switches are depressed
simultaneously, the transmitter’s RF output
power will be reduced to 0 W.
