CIRCUIT ANALYSIS
3.1.5
Power Amplifier Finals (Q2 & Q3)
Each of the Power Amplifier final devices is capable of producing 5 to 6 dB of gain. The
output signal from the Splitter is impedance-matched to each of the finals. Under
optimum conditions each final amplifies the input signal to between 50 and 70 watts
output power (depending on band split). The outputs are then impedance-matched to the
input of the Combiner. The Combiner is a printed in-phase Wilkinson type, which
combines (sums) the output power of the finals. This produces an output power of
approximately 100W (depending on band split), which is coupled to the directional
coupler (part of A1 PWB) and on to the antenna circuits. In addition, the directional
coupler samples both forward and reverse power and sends this sample to the Power
Control circuitry
.
16 dB
12 dB
Q7
SMALL SIGNAL
GAIN STAGE
PAD
EXCITER
U1
LOW LEVEL AMPL
10W
Q1
DRIVER
=40W
SPLITTER
FINALS
Q2 & Q3
6 dB
=20W
=20W
5.0 dB
5.0 dB
=60W
=60W
COMBIMER
DIRECTIONAL
COUPLER
REV
FWD
J104
RF OUT
130W (G3)
110W (G6, G7, G9, G10 & G11
90W )(G8)
THERMAL
SENSE
POWER
CONTROL
CONTROL VOLTAGE
PA KEY
FILTER A+
(4-8V) POWER SET
(2.5-4V) POWER SENSOR
-10 dB
J101
RF IN
10mW
* All power data is per miminum spec. Nominal Voltage (13.4V), 50 Ohm Load,
Room Temperature.
J1
J2
L
P
F
ANTENNA
Figure 1 - Block Diagram
3.1.6 Low Pass Filter
Following the Directional Coupler, the RF signal passes through a CHEBYSHEV LC
Low Pass filter
(19D902856G3&G9).
This passive circuit attenuates any residual
harmonics from the transmit carrier frequency and routes the signal through the RF
output to the antenna. Specifications for this filter are as follows:
Parameter
Specifications for Group 3 Specifications for Group 9
Frequency (MHz)
376-470 MHz
470-512 MHz
RF Power Handling (W)
150 Watts
150 Watts
Insertion Loss (dB)
0.4 dB
0.5 dB
Input (VSWR)
1.5:1 Maximum
1.5:1 Maximum
Output (VSWR)
1.5:1 Maximum
1.5:1 Maximum
Harmonic Attenuation (dB) 50 Minimum 760-1500
40 Minimum 940-1024
30 Minimum >1500 MHz
30 Minimum > 1500 MHz
6
LBI-38674L
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