Motorola MSF 5000 Instruction Manual page 97

Chapter 1
Description
MSF
5000
Instruction Manual
Uniboard
1-58
Power Cutback Circuit
The power cutback circuit
reduces the station output power under conditions of
high
temperature, high
VSWR, or
as
directed
by power
control circuitry.
The
cutback level of
the output can
vary
from
20 to 50%
of the rated station output
power.
This is
set
by
the
PWR CUTBACK
ADJ (R409) on the Uniboard.
If
the power control circuitry is unable
to
level the station
output power, potential
damage may occur to the station.
Any
time the power output varies
by
more then
50% of its set
value,
the
PA
Full
LED
on the
SSCB
turns off and the SSCB is
notified of
the reduced
power level.
Each stage of the PAs contain
a thermistor to measure the
operating temperature
of
the
PA
heat sink.
If
the internal temperature exceeds
100°
C, the
power
set
voltage
decreases and causes an adjustment in
the control
voltage.
If
the station contains a circulator, whenever high
VSWRs
are
applied
to the
circulator load at
high
ambient temperatures, the power set
voltage
decreases
resulting in
a
control voltage adjustment. This
causes the station
output power
to
drop below 20% of the power setting.
Transmitter Shut-down Circuit
The transmitter shut-down circuit
senses
this condition and signals
the station
control circuitry to turn off the transmitter.
This circuit
contains
two
comparators
to detect
conditions when
the power control circuit cannot level
the station
output
power.
If
the station output power is greater than its
set
value or the power control circuit
is at full drive,
the microprocessor is signaled that
a
control loop failure has
occurred.
The power
set voltage is also pulled down, reducing station output
power by
50%
in
an attempt to correct the
leveling problem.
If this condition
remains, the transmitter is shut-down.
68P81092E02
3/19/94
Chapter 1
Description
MSF
5000
Instruction Manual
Uniboard
1-58
Power Cutback Circuit
The power cutback circuit
reduces the station output power under conditions of
high
temperature, high
VSWR, or
as
directed
by power
control circuitry.
The
cutback level of
the output can
vary
from
20 to 50%
of the rated station output
power.
This is
set
by
the
PWR CUTBACK
ADJ (R409) on the Uniboard.
If
the power control circuitry is unable
to
level the station
output power, potential
damage may occur to the station.
Any
time the power output varies
by
more then
50% of its set
value,
the
PA
Full
LED
on the
SSCB
turns off and the SSCB is
notified of
the reduced
power level.
Each stage of the PAs contain
a thermistor to measure the
operating temperature
of
the
PA
heat sink.
If
the internal temperature exceeds
100°
C, the
power
set
voltage
decreases and causes an adjustment in
the control
voltage.
If
the station contains a circulator, whenever high
VSWRs
are
applied
to the
circulator load at
high
ambient temperatures, the power set
voltage
decreases
resulting in
a
control voltage adjustment. This
causes the station
output power
to
drop below 20% of the power setting.
Transmitter Shut-down Circuit
The transmitter shut-down circuit
senses
this condition and signals
the station
control circuitry to turn off the transmitter.
This circuit
contains
two
comparators
to detect
conditions when
the power control circuit cannot level
the station
output
power.
If
the station output power is greater than its
set
value or the power control circuit
is at full drive,
the microprocessor is signaled that
a
control loop failure has
occurred.
The power
set voltage is also pulled down, reducing station output
power by
50%
in
an attempt to correct the
leveling problem.
If this condition
remains, the transmitter is shut-down.
68P81092E02
3/19/94