User's Manual Part 1

AT7400 Owner Manual Rev. 2.0 – October 2006-10-23 Section 3 - 23/39
3.9.5.1 RF Hybrid Input
This hybrid equally splits the incoming RF signal, keeping the input impedance at 50ȍ level on an eventual
amplification cell malfunction. This hybrid is built out of 2 coupled transmission lines. In one end of the first
transmission line is connected the RF input signal, and on the other end a 50ȍ/10W (R1 parallel with R2) resistive
termination. On the ends of the second transmission line the coupled RF signal feeds the 2 amplification cells.
Fig.3.10: ID current adjust trim-pots location on PCB CIM 3440
3.9.5.2 UHF 12.5W Drive Amplifier – Cell A, Transistor T1
On this cell, the trim-pot TPO-1 at the same time adjusts the VGS1 voltage for T1, and the drained current ID.
Trimmers C5, C9 and C13, tunes and adjusts the input impedance. A combination among the trimmers’ physical
position and transmission lines’ length determines the bandwidth behavior. At the input, the capacitor C1 is a
input DC de-coupling, and at the output C26 as well.