Nautel XL12, Технические инструкции

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12 000 WATT AM BROADCAST TRANSMITTER
XL12
Page 4-5
01 January 2002
4.9.3 RF POWER TRIM
: The RF power level
of the selected preset RF power level can be
incrementally changed (nominal 1000 increments) by
individually pressing/releasing the RF
POWER
trim
∧ ∧
(increase) or
∨ ∨
(decrease) switches. The increments
are linear voltage steps (power=voltage
2
).
NOTE
It is recommended the current reading on the DC
AMPERES
meter and the PA volts reading on the
DC VOLTS
meter be monitored when increasing
the RF power level. Their readings must not be
allowed to exceed the levels previously recorded
for 13.5kW.
4.9.3.1 Increase RF Power:
Increase RF power
level by pressing and releasing RF
POWER
trim
∧ ∧
(increase) switch, noting a quick press and release
will increase the RF power level by one increment.
If the switch is held, its integral lamp will turn on
while it is pressed and the RF power will slew in an
increasing direction, after a 0.25s delay, until the
switch is released or until the RF power level is
13.5kW. When 13.5kW is attained, the switch's
integral lamp will turn off, even though the switch is
being pressed and any further increase in RF power
level will be inhibited.
NOTE
The RF power trim circuit controls the voltage that
determines the carrier level on/off ratio of the PDM
signals, which in turn determine the PA volts level
being applied to the RF power amplifiers. The
maximum carrier level on/off ratio that can be
attained is 45/55, which translates to 13.5kW when all
of the RF power amplifiers are contributing to the RF
output. If one or more RF power amplifiers is not
contributing, the PA volts that would provide 13.5kW
is produced but the forward power level will be less
than 13.5kW and the DC current reading will decrease
in proportion to the change in forward power. This
method of control ensures an operator cannot
overdrive the contributing RF power amplifiers when
one or more is not contributing.
4.9.3.2 Decrease RF Power:
Decrease RF power
level by pressing and releasing RF
POWER
trim
∨ ∨
(increase) switch, noting a quick press and release
will decrease the RF power level by one increment.
If the switch is held, its integral lamp will turn on
while it is pressed and the RF power will slew in a
decreasing direction, after a 0.25 second delay, until
the switch is released or until the RF power level is
0W.
NOTE
The RF output should not be set to a level that is
less than 1000 watts. Audio distortion and
unacceptable signal to noise ratios may result
with RF power levels of less than 1000 watts.
4.9.4 RF ON/OFF SELECTION:
The RF
power stage must be turned on before an RF output
can be produced. Additionally, the RF power stage
can be turned off and the transmitter retained in the
standby status without turning off the AC power
source.
4.9.4.1 RF On Selection:
The RF power stage is
turned on by pressing and releasing the
CONTROL - RF
ON
switch. Its integral lamp will turn on and remain
on, indicating the RF power stage is enabled. The
integral lamp of the
CONTROL - RF OFF switch will
turn off.
4.9.4.2 RF Off Selection:
The RF power stage is
turned off by pressing and releasing the
CONTROL -
RF OFF
switch. Its integral lamp will turn on and
remain on, indicating the RF power stage is turned
off. The integral lamp of the
CONTROL - RF ON
switch will turn off.
4.9.5 LOCAL/ REMOTE CONTROL
SELECTION:
The local/remote control selection is
described in paragraph 4.8.
4.9.6 ADJUST AUDIO LEVEL:
The
AUDIO
GAIN potentiometer on the interphase PDM drive
PWBs controls amplitude of the audio signal input to
the transmitter. Turn clockwise to increase audio
gain (and modulation depth). Turn counter clockwise
to decrease audio gain (and modulation depth).
STATUS DISPLAYS
4.10
The control/monitor panel's
STATUS
display
is provided to assist an operator/maintainer in
determining the present (real-time) status of
transmitter functions and when initiating fault
diagnostics, will identify the cause of the most recent
RF shutback. For a brief description of the purpose
and function of each display, refer to table 3-1.
4.10.1 DISPLAY COLOUR:
Each STATUS
indicator is a bicolour display. The display will be
green when the associated function/circuit is normal.
The display will be red (continuous or flashing)
when a failure has been detected or the function is
not operating within defined limits.