User's Manual Part 1

AT7400 Owner Manual Rev. 2.0 – October 2006-10-23 Section 3 - 24/39
3.9.5.3 UHF 12.5W Driver Amplifier – Cell B, Transistor 2
On this cell, the trim-pot TPO-3 at the same time adjusts the VGS2 voltage for T2, and the drained current ID.
The trimmers C35, C39 and C43, 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
C31 is a input DC de-coupling, and at the output C56 as well.
3.9.5.4 Output Combiner
The 12.5W RF signals at the output of cells A and B are combined. The combination circuit is completed with the
absorber load, R11 (50ȍ/60W). R11 dissipates the extra power in case of failure of one cell, not disturbing the
output impedance on the cell that did not fail.
3.9.5.5 Temperature Alarm
The module 4464 is protected against high temperature levels. In case the internal temperature reaches or
exceeds 149°F, (65°C). The alarm circuitry is located at PCB CIM3440, and is composed by an thermal sensor
S1, by an integrated circuit CI-3. The temperature readings are DC converted and can be measure. This DC
voltage is routed directly to the pin #7 at the CON-6 at SCU (PCB CIM3297). If the module temperature exceeds
the limits on the module 4464, as consequence, the SCU will send a command to the sub-module 4456 that
disrupts the +32V to the module 4464.