TB8100 Service Manual Power Amplifier Circuit Description 121© Tait Electronics Limited September 20067.2.3 Low Pass Filter and Directional Coupler BoardThe output from the 60W board is fed to the RF output connector via alow pass filter (LPF), to attenuate harmonics, and a dual directional coupler.The directional coupler senses forward and reverse power which is rectifiedand passed to the control circuitry for metering, alarm and power control.The directional coupler is on the output side of the LPF to measure trueforward and reflected power.7.2.4 Splitter and Combiner BoardsIn the 100W PA the output from the 6W board is split through a 3dBhybrid coupler on the splitter board to drive two 60W boards in quadrature.The outputs from these two boards are then combined by another 3dBhybrid coupler on the combiner board before being fed to the LPF/directional coupler board.7.2.5 Interconnect BoardsBecause of the modular design of the PA, interconnect boards are used incertain models to connect boards that are physically separated on theheatsink. They have no components and their only function is to link twoparts of the circuit together. The interconnect boards are shown inFigure 8.1 on page 130 and Figure 8.2 on page 131.
