Nautel XL12, Technical Instructions

Page: 122 / 238

12 000 WATT AM BROADCAST TRANSMITTER
XL12
Page 6-9
01 January 2002
6.6.13.1 Forward Power Level:
A
buffered DC voltage that is representative of the
forward power level is available at the
BFRD FWD
PWR
terminal. This voltage is a non-linear (square
law) function of the forward power level and will be
13.7 ±0.5 volts DC at 12 000 watts.
6.6.13.2 Reflected Power Level:
A
buffered DC voltage that is representative of the
reflected power level is available at the
BFRD REFL
PWR
terminal. This voltage is a non-linear (square
law) function of the reflected power level and will be
5.25 ±0.5 volts DC at 1500 watts.
6.6.13.3 RF Monitor Sample:
A true sample of
the RF output, including its modulation envelope, is
provided at remote interface PWB's
RF MONITOR
BNC coaxial connector. The
RF Monitor
output is
intended to be applied to a station modulation
monitor, but it may also be connected to an
oscilloscope during maintenance procedures. The
RF Monitor
voltage output can be set to a nominal
5.0 volts RMS, into a 50 ohm load, when the preset
power level is between 1000 watts and 12 000 watts
and the RF output is the preset level.
6.6.14 REMOTE ALARM INDICATIONS:
Outputs that indicate stress thresholds for critical
parameters have been exceeded are available on
terminals of the remote interface PWB. Each alarm
output contains a switching transistor that provides
an open collector during normal operation (non-alarm
condition) and a current-sink-to-ground when an
alarm condition exists. Each monitoring circuit must
present an impedance, between the switching
transistor and a positive DC voltage source, that will
result in a current flow of not more than 40
milliamperes. Each circuit's positive voltage source
must not exceed 24 VDC. Alarm outputs are
protected against transients and/or over voltage by a
39 volt zener diode.
NOTE
In most cases the RF output is shutback (turned
off) when an alarm condition is sensed. When
the cause of the alarm has been removed, the RF
output will be restored, at an exponential rate,
over a 200 millisecond period.
6.6.14.1 RF Stress Current Alarm:
The
RF Current Alarm
output is applied to the remote
interface PWB's
ALARM - RF CUR
terminal. During
normal operation, the output is an open collector.
When the RF output current exceeds a factory set
threshold, which represents the maximum current the
RF power modules can provide, the
RF Current
Alarm
output will be a current-sink-to-ground and the
RF output will be shutback (turned off).
6.6.14.2 AC Fail Alarm:
The AC Fail
Alarm output is applied to the remote interface
PWB's
ALARM - AC
terminal. During normal
operation, the output is an open collector. When the
AC input voltage is more than ten percent below the
ideal voltage for the power transformer's selected
primary winding taps, or a loss of phase has
occurred, the AC
Fail Alarm
output will be a
current-sink-to-ground and the RF output will be
shutback (turned off).
6.6.14.3 Battery Alarm:
The
Battery
Alarm
output is applied to the remote interface
PWB's
ALARM - BATTERY
terminal. During normal
operation, the output is an open collector. When the
battery voltage drops to 4.00 volts, output becomes a
current-sink-to-ground.
6.6.14.4 VSWR Shutback Alarm:
The
VSWR Shutback Alarm
output is applied to the
remote interface PWB's
ALARM - VSWR
terminal.
During normal operation, the output is an open
collector. When peak reflected power exceeds 1800
watts (1.35:1 relative to 12 000 watts at 100%
modulation or 14dB return loss),
VSWR Shutback
Alarm
output will be a current-sink-to-ground and RF
output will be shutback (turned off).
6.6.14.5 Cutback Alarm:
The
Cutback
Alarm
output is applied to the remote interface
PWB's
ALARM - CUTBACK
terminal. During normal
operation, the output is an open collector. When the
output has been attenuated from three or more
shutback events, the transmitter will be in cutback
mode. When the transmitter is in cutback mode, the
output will be a current-sink-to-ground. The RF
output will be cutback (reduced) by an amount that is
proportional to the amount SWR counter's count
exceeds three.