Nautel XL12, Technical Instructions

Page: 31 / 238

12 000 WATT AM BROADCAST TRANSMITTER
XL12
Page 2-7
01 January 2002
2.1.8.5 System Reset:
The
system reset
circuit
generates reset pulses which are applied to the
AC/DC power, exciter and RF power stages. It also
resets any alarm circuit that is/was latched in its
alarm state. It must be configured to be controlled
by a single ended input (see figure 2-1) or by a
differential input (see figure 2-2). The
SYSTEM RESET
terminals are TB2-1(+) and TB2-2(-). The
associated 3-pin header/2-socket shunt post on the
remote interface PWB is E13.
2.1.8.6 Alarm Recall:
The
alarm recall
circuit
allows the user to reinstate an active remote alarm
condition for any alarm(s) that caused the last RF
shutback and is not currently being displayed or
affecting the RF output. It must be configured to be
controlled by a single ended input (see figure 2-1) or
by a differential input (see figure 2-2). The
ALARM
RECALL terminals are TB2-3(+) and TB2-4(-). The
associated 3-pin header/2-socket shunt post on the
remote interface PWB is E14.
2.1.9 OTHER REMOTE CONTROLS:
An
RF inhibit control can be connected, at the user's
discretion. This input will influence the transmitter's
RF output regardless of the selected control location
(
LOCAL or REMOTE ).
2.1.9.1 External PDM (RF) Inhibit Control:
The external PDM inhibit circuit reduces the 'on'
time of the PDM signal to near zero, effectively
turning off the RF output (a residual RF leak of
approximately 10 watts may be present) the instant
an active condition is applied. This state is
maintained as long as the active condition exists. It
must be configured to be controlled by a single ended
input (see figure 2-1) or by a differential input (see
figure 2-2).
PDM INHIBIT terminals are TB2-5(+) and
TB2-6(-). The associated 3-pin header/2-socket
shunt post on the remote interface PWB is E15.
NOTE
The external PDM inhibit input is intended to be used
in conjunction with antenna switching circuitry to
ensure minimal RF output current flows during
opening/closing of contacts in the transmitter's RF
feed cable. An active 'PDM inhibit' condition must be
applied prior to contact opening (disconnecting the RF
load) and must be maintained until contact closure has
occurred and an appropriate impedance has been
connected to the transmitter's RF output. The RF
output will be instantly restored to its original level
when the active condition is removed.
2.1.10 RF PERFORMANCE MONITORING:
The transmitter provides outputs to monitor RF
performance. They include DC voltages which are
representative of the forward power level, the
reflected power level and the DC voltage being
applied to the RF amplifiers. In addition, a true RF
sample of the RF output's voltage waveform is
available for external monitoring. These outputs are
available on the remote interface PWB.
2.1.10.1 RF Monitor Sample :
A true sample of
the RF output's voltage waveform, including its
modulation envelope, is provided at a BNC connector
(
RF MONITOR
) on the remote interface PWB. The
RF
monitor
output is intended to be applied to a station
modulation monitor with a 50-ohm input impedance.
It may also be monitored by an oscilloscope during
maintenance procedures. The
RF monitor
output
can be set to provide 5.0 volts RMS for each preset
power level, provided the power levels are preset to
a level between 1000 and 12 000 watts.
2.1.10.2 Forward Power Level:
A buffered DC
voltage that is representative of the forward power
level is available on TB4-1 (
BFRD FWD PWR ) [TB4-2
( GND ) is the return path]. This voltage is a non-linear
(square law) function and will be 13.7 ±0.5 VDC
when the forward power is 12 000 watts. The
impedance of the monitoring circuit must be greater
than 1000 ohms.
2.1.10.3 Reflected Power Level:
A buffered
DC voltage that is representative of the reflected
power level is available on TB4-3 (
BFRD REFLD PWR )
[TB4-2 ( GND ) is the return path]. This voltage is a
non-linear (square law) function and will be
5.25 ±0.5 VDC when the reflected power is 1500
watts. The impedance of the monitoring circuit must
be greater than 1000 ohms.
2.1.10.4 Power Amplifier Volts:
A buffered DC
voltage that is directly proportional to the DC voltage
being applied to the RF amplifiers in the RF power
modules is available on TB4-5 (
BFRD PA VOLTS
)
[TB4-4 (
GND
) is the return path]. This voltage will be
2.85 VDC when the DC voltage being applied to the
RF amplifiers is 129 VDC. The impedance of the
monitoring circuit must be greater than 1000 ohms.