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cycle to minimize contact bounce problems
in the Raise-Lower switches (Local
or
Re-
mote). Raise
or
Lower inputs are routed to
integrated circuits U20B and U20A which
gate the pulses from integrated circuit U 17F
to the proper integrated circuit U27 input.
The
output
of
integrated
circuits
U27
-
U21
is buffered by integrated circuit U28 and
connected to integrated circuits U29, U30
and U31. Integrated circuit U30 is a top-
limit sensor,
in
that it changes its output
when all
of
its inputs are
in
the
"HIGH"
state (maximum count). This inhibits inte-
grated circuit U20B and prevents further
counting in the
"UP"
direction. Similarly,
integrated circuit U29 senses the bottom
condition,
inhibiting
integrated
circuit
U20A and preventing further counting in
the
"DOWN"
direction.
Integrated circuit U31 is a Digital-to-An-
alog converter, providing
an
output in the
range
of
O (for an input count
of
0) to -10
volts (for an input count
of
255). Integrated
circuit
UllA
inverts this voltage so that it
is in the range
of
O to +
2V.
This APC Level
signal is connected to the APC integrated
circuit U4B. Note that the count cannot
be
changed during a power failure, as inte-
4-6
grated circuits U20B and U20A have inputs
connected to the Power/Enable circuit.
The basis for developing power control
voltage for the transmitter is integrated cir-
cuit
U4B.
The
control
voltage
is
sent
through the APC line to the Exciter where
it sets the output drive level. With the APC
switch, S5,
in
the
OFF
position, the gain
of
U4B is set by RIO and
Rll.
U4B simply
acts as a non-inverting amplifier. The power
control voltage from the D-to-A converter
is fed to U4B-5.
As
the voltage increases,
the output from U4B-7 increases. This volt-
age is then divided down by
Rl9,
Rl/5-12
and R60 when
SS
is
in
the APC
OFF
posi-
tion. R19 sets the maximum voltage and
hence, the maximum power available from
the exciter in the APC
OFF
mode. When
SS
is switched to the APC ON position, the
gain
of
U4B is set by
Rl2
and R13. The
sample
of
the output power now is directed
to the inverting input, U4B-6. Therefore,
when the power output increases, the output
of
U4B will decrease to keep the power the
same. In the APC
ON
condition, the output
of
U4B is divided down by R20, Rl/6-11,
and R60. R20 sets the operating gain
of
the
APC loop and determines the maximum
drive available from the Exciter.
888-2312-001
The
reflected
power
sample output at
U5A-1 is connected to U5B-5 which is a
comparator for
SWR
protection.
If
the
re
-
flected power exceeds the reference level
established by R64 (VSWR TRIP SET),
then USB will
tum
on Q4 and reduce the
forward
power
until the reflected power is
below the reference defined by
R64.
USB
also drives transistor QS which drives the
front panel and remote
SWR
alarm circuits.
4.8.6.
User
Interface
RFI
Filter
and
Transient Protection
All user control input, monitoring and out-
put
connection lines are brought out to a
WAGO block
on
the 1/0 board
on
the rear
panel
of
the controller chassis. All the inputs
and outputs are RPI filtered and transient
protected for maximum system reliability.
4.8.7.
AC
Power
Distribution
All
AC
power is brought in through the
AC
Power Distribution Panel. In addition to
providing ac interconnection to the differ-
ent power amplifiers and the Exciter, it con-
tains the main circuit contactor and the line
transient protection devices which isolate
and protect the transmitter from most ser-
vice entrance disturbances.
WARNING: Disconnect primary power prior to servicing.
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