Nautel FM10, Technical Instructions

Page: 107 / 200

10 000 WATT FM BROADCAST TRANSMITTER
FM10
Page 6-6
15 November 1999
6.3.7.6.2 3 Phase Rectifier Assemblies : Each 3-
phase rectifier assembly (A2 and A3) contains a
thermistor whose output is applied to the
Rectifier
Temp 1 (J12-5) and Rectifier Temp 2 (J12-1) inputs
of the power supply control PWB. Comparators on
the power supply control PWB monitor the inputs. If
the temperature exceeds 90
°
C in one or both of the
rectifier assemblies, 0.0 VDC is applied to the
Rectifier Temp Alarm output (J11-2), which is
applied to the control/monitor PWB and the
RECT
TEMP alarm LED is turned on. When the control/
monitor PWB detects a rectifier temperature alarm, it
immediately turns the
PA Volts Control and IPA
Volts Control inputs down to 0.0 VDC - effectively
turning off the switching power supplies (A thru F)
and the IPA switching power supply
.
6.3.7.7 Fan Failure Detection: The two DC fans
in each fan assembly (A27 and A28) and the two DC
fans on the rear, lower panel have tachometer outputs
which are applied to
Fan Tach 1 thru 6 inputs of the
power supply control PWB. If one of the fans has
failed or is turning at a greatly reduced speed, the
FAN FAIL
alarm LED will turn on and 15 VDC will
be applied to the Fan Fail Alarm output, which is
applied to the control/ monitor PWB.
6.3.7.8 Switching Power Supply Module Inhibit:
If the control/monitor PWB detects a high
temperature condition on one or more of the RF
power modules or a low RF drive input to one or
more of the RF power modules, 15 VDC will be
applied to the associated
PDM inhibit ( A thru F )
inputs of the power supply control PWB to turn off
the switching power supply corresponding to the RF
power module with the failure condition.
6.3.7.9 Alarm Reset: Momentarily pressing
ALARM RESET
switch on the transmitter's control/
monitor panel will cause 15 VDC to be applied to the
Alarm Reset input (J11-5). This resets all latched
alarms on power supply control PWB provided the
alarm condition has been cleared. If an alarm LED is
turned on and the fault condition is still present, then
the alarm LED will not be turned off by simply
pressing the
ALARM RESET
switch. Momentarily
pressing the
LAMP TEST
switch on the transmitter's
control/monitor panel will cause 0.0 VDC to be
applied to the
LED Test input (J11-3). This turns on
all alarm LEDs on the power supply control PWB as
long as the
LAMP TEST
switch is pressed.
RF POWER STAGE
6.4
See figures SD-6 and SD-7. The RF
power stage generates the final RF output. It consists
of PA input power probe A16, IPA module A17,
intermediate RF drive splitter A15, six RF power
modules [A18 (A) thru A23 (F)], RF combiner/final
filter A24 and RF power probe A25.
6.4.1 IPA INPUT POWER PROBE: See
figure SD-6. The IPA input power probe (A16)
accepts the nominal 20 watt RF output from a
suitable exciter and applies it as the
RF Drive input
(W40P2) to the IPA module. A current sample from
T1 and a voltage sample from the C1/C2 voltage
divider provide a forward power sample of the
exciter's output as the
IPA RF Drive Level output to
the control/monitor PWB. C2 is adjusted for
optimum directivity.
6.4.2 INTERMEDIATE POWER
AMPLIFIER (IPA) MODULE: See figure SD-6.
IPA module A17 accepts the nominal 20 watt RF
output from the IPA input power probe as its
RF
Drive input (W40P2). This input is split to drive two
IPA RF power amplifiers. The RF output of the two
amplifiers is controlled by the
IPA Volts (P41-1) level
from the AC/DC power supply. The two RF outputs
are applied to the intermediate RF drive splitter. The
Temp (IPA) output (P4-7) is applied to the
control/monitor PWB to sense excessive IPA
temperature. The
PA Fail (IPA) output (P4-3) is
applied to the control/monitor PWB to sense a failed
IPA amplifier.
6.4.3 INTERMEDIATE RF DRIVE
SPLITTER: See figure SD-6. The intermediate RF
drive splitter assembly (A15) combines the two RF
outputs from the IPA module, provides forward and
reflected power monitoring of the IPA output and
provides a splitter with six equal, phase coherent
signals to drive the RF power modules.
6.4.3.1 IPA Combiner: The IPA combiner
sections combine the two RF outputs from the IPA
module to produce a nominal 375 watts used as the
RF drive input to the IPA output splitter section. The
Wilkinson type hybrid combiner, realized with
microstrip transmission lines on a PWB ard, provides
good mutual isolation between the input ports.
Amplitude and phase imbalances between the inputs
cause power dissipation in resistor R16.