User Manual

MXi DUAL PALLET POWER AMPLIFIER HEATSINK ASSEMBLY
PUB06-80 Rev 1 July 17, 2007 06-80-2 MXi Dual Pallet Power Amplifier Heatsink Assembly
2 FRONT END MODULE ASSEMBLY 21B1473G1
The front end module performs several distinctive functions. Firstly, it serves as a pre-amplifier, which boosts the
signal from the up-converter by approximately 9dB. This module also contains a phase shift circuit and a variable
attenuator; both adjustments are available and set to maximum and do not need to be adjusted in the MXi
amplifier. These circuits are only used for adjusting phase and gain balance between two paralleled amplifiers.
Figure 2 Front End Module
The RF signal is fed to the amplifier through hybrid HY1 and attenuator P-AT1. Refer to Figure 9.
HY1, along with associated components CR1, CR2, C1 through C6, R1, R2 and RV1 act as a phase shifter. P-
AT1 is a variable attenuator. The attenuation is controlled by RV2. Typically, RV2 is adjusted for minimum
attenuation (fully clockwise) during the bench testing of the module. Once this is done, RV2 is not adjusted again.
U1 is a hybrid linear amplifier with a nominal gain of 17.5dB. The typical operating point of the amplifier in this
application is well below the 1 Watt rating of the hybrid.
The power to the Front-End module (+32VDC) comes in at TP2.
The control voltage at TP1 comes from the AGC and VSWR cutback circuit in controller board. This voltage
corresponds to the output power of the final amplifier. If the AGC circuit is enabled and the output power tries to
increase, TP1 voltage increases, thus maintaining the output at the pre-set level. Similarly, if the reflected power
increases past the VSWR cutback setting, TP1 increases and the output power is reduced.
The higher the voltage at TP1, the higher the attenuation in the module, therefore, lower the overall output power.
RF STATUS (TP3) and as mentioned above the PHASING control (RV1) and GAIN control (RV2) are other
features of this module which are not applicable to the MXi 201U amplifier.