Powerwave Technologies 5JS0047 Tornado, Model NTGY71AA User Manual 4

Powerwave Technologies Inc Tornado, Model NTGY71AA 4

sect 4

044-05080 Rev. A 4-1PRINCIPLES OF OPERATION4-1. INTRODUCTIONThis section contains a functional description of the multichannel power amplifier (MCPA).4-2. RF INPUT SIGNALThe maximum input power should not exceed the limits specified in table 1-1.4-3. RF OUTPUT LOADThe load impedance should be as good as possible (1.5:1 or better) in the working band for goodpower transfer to the load.4-4. AMPLIFIER FUNCTIONAL DESCRIPTIONThe NTGY71AA amplifier (figures 1-1 and 4-1) is a linear, multichannel power amplifier that operatesin the 25 MHz frequency band from 869 MHz to 894 MHz at an output power of 70 watts. Eachamplifier is a self-contained module and is functionally independent of any other amplifier modules inthe system. Each amplifier module has an alarm board that monitors the amplifier performance. Ifa failure or fault occurs in an amplifier module, it is transmitted to the host system via an RS485interface.The amplifier is compliant to the requirements of FCC Part 22 with respect to spurious emissions(see table 1-1). Constant gain is maintained by continuously comparing active paths with passivereferences, and correcting for small variations through the RF feedback controls. All gain variations,for example those due to temperature, are reduced to the passive reference variations. The amplifiermodule is comprised of:An input amplifierA driver amplifierA main amplifierA multifunction board4-4.1. INPUT AMPLIFIERRF is fed to the input amplifier, which consists of a bandpass filter, VVAs, and phase shifters forgain control and phase sweeping functions. They are controlled by a microprocessor on themultifunction board. At its output, the input amplifier splits the signal to the driver amplifier andcarrier cancellation circuits.4-4.2. DRIVER AMPLIFIERThe driver amplifier consists of two stages of class AB amplification which provide approximately 40dB of gain in the 25 MHz frequency band from 869 MHz to 894 MHz. The amplifier operates on +26Vdc, and a safe bias voltage which is controlled by microprocessors.Section4
044-05080 Rev. A 4-24-4.3. MAIN AMPLIFIERThe main amplifier employs two class AB amplification stages for maximum efficiency. It providesapproximately 25 dB of gain in the 25 MHz frequency band. The output from the main amplifier istypically 50.2 dBm. The amplifier operates on +26 Vdc, and gate bias voltages controlled bymicroprocessors.4-4.4. MULTIFUNCTION BOARDThe multifunction board consists of control and alarm circuits. The MCPA communicates to thehost system through the multifunction board which gathers the status information of the amplifierand reports to the host system via the RS485 interface when instructed. It also protects the MCPAfrom adverse conditions such as overpower, input overdrive, overvoltage, etc. A microprocessor onthe multifunction board also controls two loops in the feed-forward system.4-5. AMPLIFIER MODULE COOLINGEach amplifier module is contained within a thermally conductive chassis which, when properlymounted on an adequate thermal surface, will provide sufficient cooling to maintain the amplifierwithin the specified operating temperature range.4-6. POWER DISTRIBUTIONPrimary DC power for the amplifier is provided by the host system. The amplifier generates all therequired voltages internally from the main source.RFININPUTAMPLIFIERMAINAMPLIFIERRFOUTMULTIFUNCTION BOARD(ALARMS AND LOOP CONTROLS)DRIVERAMPLIFIERFigure 4-1. NTGY71AA Multichannel Power Amplifier Functional Block Diagram

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