500 WATT RADIOBEACON TRANSMITTER
ND2000A-02X-xx0
Page
3-14
15 January 2005
(h) Adjust or verify antenna tuning unit is adjusted
(by personnel at antenna tuning unit site) in
accordance with instructions in the ATU
instruction manual.
(i) On completion of antenna tuning unit
adjustment, set the
TEST-Power/Mod
switch to
REFL PWR
and verify the reflected power
indication on the
TEST-Power/Mod
meter is less
than five percent of the forward power reading
(25 watts maximum).
(j) Repeat procedures detailed in paragraph 3.12
for the standby (side B) side of the subject
transmitter.
THIRD STAGE (INITIAL START-UP)
3.13
The third stage of initial start-up is to
establish the RF output level (intended carrier level)
that will provide the desired field strength at the
required distance from the antenna, the correct setting
(
CUR
or
VOLT
) of
RF MON
switch A9A2S1 and the
optimum modulation percentage intended modulation
depth for the antenna system in use; by operating a
transmitter, that has met the requirements of the first
stage of initial start-up (successfully completed the
functional test/adjustment procedures detailed in
paragraph 5.3), into an antenna system that has met
the requirements of the second stage of initial start-up.
3.13.1
INTENDED CARRIER LEVEL:
The
intended carrier level is the unmodulated RF output
that will provide the desired field strength at the
required distance from the antenna. Once established,
the intended carrier level should be recorded in the
Established Reference
section of table 5-2 and should
be used in all subsequent functional test/adjustment
procedures. Using procedures detailed in paragraph
5.5.4, adjust
O/P POWER
potentiometer A4A2R48
when side
A
is selected until the desired field strength
at the required distance from the antenna is attained.
Ensure the unmodulated RF output does not exceed
500 watts.
When the intended carrier level has been determined,
set the
SELECT MAIN TX
switch to
B
and adjust
O/P
POWER
potentiometer A5A2R48 for the intended
carrier level.
NOTE
If the intended carrier level is less than 500 watts, it
will be necessary to adjust the carrier level fault
threshold level, while operating into the antenna
system, as detailed in paragraph 5.3.15.2.
3.13.2 RF MONITOR SIGNAL SOURCE
SELECTION:
The source of the RF output
information available on
RF MON
connector A9A2J3
is determined by the setting of
RF MON
switch
A9A2S1. When
RF MON
switch A9A2S1 is set to
CUR
, a sample of the RF output current waveform is
provided. When
RF MON
switch A9A2S1 is set to
VOLT
, a sample of the RF output voltage waveform is
provided. The correct setting for this switch is the
setting which provides the waveform with the greatest
modulation depth (percentage). Once established, the
setting of
RF MON
switch A9A2S1 should be recorded
in the
Established Reference
section of table 5-2 and
RF MON
switch A9A2S1 should be set to the recorded
setting.
3.13.3
INTENDED MODULATION DEPTH:
The intended modulation depth is the optimum
modulation depth that can be attained (as close as
possible to 95%) with the antenna system in use.
Once established, the intended modulation depth
should be recorded in the
Established Reference
section of table 5-2 and should be used in all
subsequent test/adjustment procedures.
Reduce modulation percentage immediately if the
RF
CURRENT
lamp turns on. Failure to observe this
precaution may result in excessive current flow in
the power amplifier stage and cause failure of solid
state devices.
- If
RF CURRENT
lamp turns on, the RF stress
current threshold is being exceeded. Reduce
mod depth immediately to a level that results in
RF CURRENT
lamp turning off.
- If
SWR ALARM
lamp turns on, the carrier level
will be cutback and it will not be possible to
maintain the intended carrier level. Reduce mod
depth until
SWR ALARM
lamp turns off.
