E.F. Johnson Company 242-20X1-213, Руководство пользователя

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CIRCUIT DESCRIPTION
6-12
August 2000
Part No. 001-2001-200
6.3.3 FINAL AMPLIFIERS
Q502 and Q503 are combined 60W amplifiers. The
10W RF input from the driver U501 is applied to a 70.7
ohm Wilkinson splitter and then to the gate of each
MOSFET amplifier. The 60W outputs on the drain of
the amplifiers are combined using a Wilkinson combin-
er. Q502 has a half-wave transmissionline on the input
and Q503 has a half-wave on the output. These T-lines
are used to drive the 60W amplifiers out of phase. The
output of the combiner is fed from WO513 directly to
the forward/reverse power detect board.
The Wilkinson splitter and combiner provide the
capability to split the drive input and combine the
final outputs while maintaining isolation between the
two final amplifiers. The combiner consists of two
quarter-wave transmission lines and a balancing resis-
tor. During normal operation, a signal of relatively
equal phase and amplitude is present on both ends of
the balancing resistor. Therefore, no current flows and
no power is dissipated in the balance resistor. If one
final failed, the other final of a pair would continue to
function.
6.3.4 POWER DETECTORS
The supply current is monitored through a resis-
tor that creates a current output level indicative of the
power output. The outputs of U503, U504 and U505
are monitored by the Universal Station software
through the RF Interface Board. If a final amplifier
fails, the software will reduce the output power to pre-
vent over-driving the remaining final amplifier.
6.3.5 THERMAL SENSOR
Thermal protection is provided by temperature
sensor U507. The operating range of the sensor is
from -30
°
C to 100
°
C (-22
°
F to 212
°
F). Amplifier
U506A sends the output of U507 through WO509 to
the RF Interface Board. The RF Interface Board
reduces the power amplifier to half power (via the
MPC) if the temperature reading is too high and turns
the fan on and off (not via the MPC). The fan is
turned on at approximately 50
°
C and off again at
42
°
C.
6.3.6 FORWARD/REVERSE POWER DETECT,
CIRCULATOR, LOW-PASS FILTER
The power amplifier output is directly coupled to
the forward/reverse power detect board via a jumper.
The output then enters the circulator and exits to the
low-pass filter board and the antenna jack for a mini-
mum power output of 110W at the default setting. If
an antenna is not connected, the circulator connects
the output power to R685.
Forward and reverse power are electromagneti-
cally coupled from the input and reflected ports of the
circulator. R663/R680 calibrate the forward and
reverse sense levels. The sensed levels are coupled to
the RF Interface Board and software.
Figure 6-6 110W POWER AMPLIFIER BLOCK DIAGRAM
POWER CONTROL
DRIVER CURRENT
FINAL 1 CURRENT
FINAL 2 CURRENT
TEMPERATURE SENSOR
Q501
PRE-DRIVER
U501
DRIVER
RF IN
U503
Q502
FINAL 1
FINAL 2
Q503
U504
AMP
TEMP SENSE
U507 U506A
U502
U509
U601A/B
FORWARD
POWER
U651A/B
REVERSE
(REFLECTED)
POWER
LPF RF OUTPUT
RF LOAD