RADIOBEACON TRANSMITTER
ND500II (125 WATTS) DOUBLE SIDEBAND - NO VOICE
Page 3-12
15 September 2003
THIRD STAGE (INITIAL START-UP)
3.13
The third state of initial start-up is to
operate a transmitter that has met the requirements of
the first stage of initial start-up into an antenna
system that has met the requirements of the second
stage of initial start-up, and then perform a functional
test and determine the optimum carrier level and
modulation depth settings.
3.13.1
INTENDED CARRIER LEVEL
:
Adjust the carrier level during range tests to
determine the RF output power required to obtain the
desired range. Once established, this RF output
power level should be recorded as the 'intended
carrier level' in the 'Established Reference' section of
table 5-2 and should be used in all subsequent
calibration and minimum performance test
procedures.
NOTE
If the 'intended carrier level' is less than 125 watts,
it will be necessary to recalibrate the carrier level
fault threshold level (5.3.8.2), modulation depth
fault threshold level (5.3.8.3), and the overmod
alarm threshold (5.3.10); with the transmitter
operating into a dummy load.
3.13.1.1
RF Monitor Signal Source Selection:
The source of the RF output information available on
RF MON
connector TB6-4/5 is determined by the
setting of
RF MON
switch A7S1. When
RF MON
switch A7S1 is set to
CUR
, a sample of the RF output
current waveform is provided. When
RF MON
switch
A7S1 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 A7S1 should be recorded in the
'Established Reference' section of table 5-2 and
RF
MON
switch A7S1 should be set to the recorded
setting.
3.13.2
INTENDED MODULATION DEPTH
:
Monitor the RF output waveform at
RF MON
connector J1, using an oscilloscope, when the carrier
level has been set to the 'intended carrier level' and
the modulation depth has been set to the maximum
possible percentage without causing clipping or
distortion. If the modulation envelope on the
oscilloscope waveform is clipped or distorted, reduce
the modulation depth, by adjusting
MOD %
potentiometer A4R2, until the modulation envelope is
free from clipping and/or distortion. Once
established, this modulation depth should be recorded
as the 'intended modulation depth' in the 'Established
Reference' section of table 5-2 and should be used in
all subsequent calibration and minimum performance
test procedures.
NOTE
If the 'intended modulation depth' is less than 95
percent, it will be necessary to recalibrate the
modulation depth fault threshold level (5.3.8.3) with
the transmitter operating into a dummy load.
