Powerwave Technologies 5JS0046 Hurricane, Model NTGY81AA User Manual 4

Powerwave Technologies Inc Hurricane, Model NTGY81AA 4

sect 4

044-05079 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 NTGY81AA amplifier (figures 1-1 and 4-1) is a linear, multichannel power amplifier that operatesin the 60 MHz frequency band from 1930 MHz to 1960 MHz at an output power of 50 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 predistortion amplifierA driver amplifierA main amplifierA multifunction board4-4.1. INPUT AMPLIFIERRF is fed to the input amplifier, which consists of an isolator at the input, bandpass filter, VVAs,and phase shifters for gain control and phase sweeping functions. They are controlled by amicroprocessor on the multifunction board. At its output, the input amplifier splits the signal to thepredistortion amplifier and carrier cancellation circuits.4-4.2. PREDISTORTION AMPLIFIERThe predistortion amplifier predistorts the input signal in a way that it linearizes the output of themain amp at 50 watts. It also contains the main loop VVAs and phase shifters. All the predistortionvoltages and loop voltages are controlled by a microprocessor.Section4
044-05079 Rev. A 4-24-4.3. DRIVER AMPLIFIERThe driver amplifier consists of two stages of class AB amplification which provide approximately 40dB of gain in the 60 MHz frequency band from 1930 MHz to 1990 MHz. The amplifier operates on+26 Vdc, and a safe bias voltage which is controlled by microprocessors.4-4.4. MAIN AMPLIFIERThe main amplifier employs two class AB amplification stages for maximum efficiency. It providesapproximately 25 dB of gain in the 60 MHz frequency band. The output from the main amplifier istypically 48.6 dBm. The amplifier operates on +26 Vdc, and gate bias voltages controlled bymicroprocessors.4-4.5. 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.RFININPUTAMPLIFIERPREDISTORTIONAMPLIFIERDRIVERAMPLIFIERMAINAMPLIFIERRFOUTMULTIFUNCTION BOARD(ALARMS AND LOOP CONTROLS)Figure 4-1. NTGY81AA Multichannel Power Amplifier Functional Block Diagram

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