M/A-Com 19D902797G1, Руководство по обслуживанию

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CIRCUIT ANALYSIS
POWER AMPLIFIER
The power amplifier section of the PA Board consists of
an Exciter, a Low Level Amplifier, a Driver, and the Power
Amplifier Finals. All these gain stages have an input and output
impedance of 50 ohms. Figure 1 is a block diagram showing
the signal flow within the Power Amplifier Assembly.
Exciter (UIOI)
The Exciter stage uses a broadband silicon monolithic
microwave integrated circuit (MMIC) amplifier. The signal
from transmitter synthesizer, typically 10 dBm (10 mW), is
input to the Exciter through a 10 dB resistive pad (R100 &
R102). The Exciter amplifies the resulting 0 dBm (1 mW)
signal to 20 dBm (100 mW). Following the Exciter is a 3 dB
resistive pad (R104 & R106). This attenuator reduces the
MMIC output power to 17 dBm (50 mW).
The MMIC requires a 5 volt supply source. The 8 volt
regulator (U100) provides the 5 volts to the MMIC via a
dropping resistor R103.
Low Level Amplifier (U1O2)
The Low Level Amplifier (LLA) stage uses a 50 ohm thick
film RF Power Module to amplify and control of the output
power. Internally, the module is a two stage amplifier. The
power control circuitry controls the gain of the first stage by
varying the collector voltage of Q203. The second stage gain
remains constant with A + providing the DC supply voltage.
The signal from the Exciter stage, typically 17 dBm (50
mW), is input into the LLA. Under maximum Power Set
conditions, the LLA amplifies the signal to a typical output
level of 40 dBm (10 W).
Driver (Q101)
The driver is a 6 dB RF amplifier. A network consisting of
C114, C117 and C139 and L103 and L105 provides interstage
impedance matching between U102 and Q101. The signal from
the LLA, typically 40 dBm (10 W), is amplified to 46 dBm (40
W). Impedance matching between the driver output and the
input to U103 is provided by C145, C148, C152, C153, and
L108. The splitter, U103, is a quadrature 90° hybrid coupler. It
divides the signal and applies equal power to the two Power
Amplifier Finals, Q102 and Q103.
Copyright© 1992-2002, M/A-COM Private Radio Systems, Inc. All rights reserved.
TABLE 1 - GENERAL SPECIFICATIONS
ITEM SPECIFICATION
FREQUENCY 136 MHz - 174 MHz
OUTPUT POWER 65 watts - 135 watts (into Low Pass Filter)
INPUT POWER (RF) 10 mW min. into 2:1 VSWR
TEMPERATURE RANGE 30°C TO + 60°C (Ambient air)
SUPPLY VOLTAGE 13.4 Vdc
CURRENT 29 Amps max. (25 A typical @ 135W, 13.4V)
DUTY CYCLE Continous
STABILITY Stable into 3:1 VSWR; all temp. ,voltage, freq. 65 watts -
135 watts
RUGGEDNESS AT HIGH VSWR No damage into open or short load.
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This manual is published by M/A-COM Private Radio Systems, Inc., without any warranty. Improvements and changes to this manual
necessitated by typographical errors, inaccuracies of current information, or improvements to programs and/or equipment, may be made by
M/A-COM Private Radio Systems, Inc., at any time and without notice. Such changes will be incorporated into new editions of this manual.
No part of this manual may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying and
recording, for any purpose, without the express written permission of M/A-COM Private Radio Systems, Inc.
LBI-38531G
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