User Manual

MCA9129-90-A Installation & Service Manual

044-05060 Rev. C 4-3 July 2001November 2002

and phase variations, for example those due to temperature, are reduced to the passive reference

variations. The amplifier module is comprised of:

Preamplifiers

Main amplifier

Error amplifier

Two feed-forward loops with phase-shift and gain controls

DC/DC power regulator

Alarm monitoring, control and display panel

The main amplifier employs class AB amplification for maximum efficiency. The error amplifier

and feed forward loops are employed to correct signal nonlinearities introduced by the class AB

main amplifier. The error amplifier operates in class AB mode. The RF input signals are ampli-

fied by a preamp and coupled to an attenuator and phase shifter in the first feed-forward loop.

The main signal is phase shifted by 180 degrees and amplified in the premain amplifier. The out-

put from the premain amplifier is fed to the class AB main amplifier. The output from the main

amplifier is typically 120

140 watts. The signal is output to several couplers and a delay linefilter.

The signal output from the main amplifier is sampled using a coupler, and the sample signal is

combined with the main input signal and input to the second feed-forward loop. The error signal is

attenuated, phase shifted 180 degrees, then fed to the error amplifier where it is amplified to a

level identical to the sampled output from the main amplifier. The output from the error amplifier

is then coupled back and added to the output from the main amplifier. The control loops continu-

ously make adjustments to cancel out any distortion in the final output signals.

The primary function of the first loop is to provide an error signal for the second loop. The primary

function of the second loop is to amplify the error signal to cancel out spurious products devel-

oped in the main amplifier. The input signal is amplified by a preamplifier and fed to a coupler and

delay line. The signal from the coupler is fed to the attenuator and phase shifter in the 1st loop.

The first loop control section phase shifts the main input signals by 180 degrees and constantly

monitors the output for correct phase and gain.