Quantcast CHAPTER 5 AMPLIFIER,  RADIO  FREQUENCY  AM-7238/VRC MAINTENANCE   INSTRUCTIONS

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Page Title: CHAPTER 5 AMPLIFIER, RADIO FREQUENCY AM-7238/VRC MAINTENANCE INSTRUCTIONS
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PACKING STATIC SENSITIVE MODULES.  Continued - TM-11-5820-890-30-5_528
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TM-11-5820-890-30-5 Ground Non-Icom Radio Sets Consisting of: Receiver-Transmitter Radio RT-1439/VRC (NSN 5896-01-195-0827) Manual
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OVERALL  FUNCTIONAL  DESCRIPTION.  Continued


TM 11-5820-890-30-5 CHAPTER 5 AMPLIFIER,  RADIO  FREQUENCY  AM-7238/VRC MAINTENANCE   INSTRUCTIONS Subject Section Page Principles of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I 5-1 Repair Parts, Special TooIs, TMDE, and Support Equipment . . . . . . . . . . . . . . . . . . . . . . . II 5-4 Troubleshooting Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III 5-4 Maintenance Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IV 5-32 Preparation for Storage or Shipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V 5-39 Section  I.  PRINCIPLES  OF  OPERATION Subject Para Page Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1 5-1 Overall Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-2 5-1 Input Control Signal Paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3 5-2 RF Signal Paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4 5-3 Feedback and Output Signal Paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-5 5-3 5-1. INTRODUCTION. The power amplifier increases the 4-W output of the RT to 50 W for long range communication. It has no controls or  indicators.  When  properly  installed  in  a  vehicular  radio,  operation  is  automatic. The  power  amplifier  separates  into  three  parts: Case,  Amplifier,  RF  6A1  (power  amplifier  case). Circuit  Card  Assembly,  Decoder  Control  6A2  (decoder  control). Electronic   Component   Assembly   -  Amplifier,  Radio  Frequency  6A3  (power  amplifier  heat  sink). The  power  amplifier  case  contains  filters,  electronic  switches,  and  the  three  external  connectors.  The  decoder control  provides  the  signal  interface  to  the  RT.  The  power  amplifier  heat  sink  contains  the  RF  amplifier  that provides  the  RF  gain. 5-2. OVERALL  FUNCTIONAL  DESCRIPTION. Figure 5-1 is a block diagram of the power amplifier. During high power transmit, the RF signal from the RT is input at  connector  J2.  It  is  routed  through  an  RF  switch  to  the  amplifier.  The  amplifier  increases  the  power  level  to 50 W. The amplified signal is routed through one of three filters to reduce harmonic and spurious signals. From there,  it  goes  through  a  second  RF  switch  and  out  the  ANT  connector  (J1). During low power transmit, the RF signal is routed from J2 through the two RF switches to J1. During receive, the same  path  is  followed  in  reverse. Control signals from the RT identify the frequency band and the RF path required. The decoder control activates the  high  voltage  switch  drivers  based  on  the  control  signals  from  the  RT.  The  switch  drivers  select  the  switch positions  that  determine  the  RF  path. Feedback signals are provided during high power transmit. Internally, an automatic level control (ALC) signal is used to control the RF gain. If the VSWR is too high, the RF gain is reduced and the sidetone disable line to the RT is  activated.  The  decoder  control  also  drives  the  RT  SIG  display. 5-1


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