3.2 Pre-Amplifier
The input of the amplifier uses two stages of class AB amplification that provide
approximately 13.5 dB of gain in the 5 MHz band from 935 MHz to 940 MHz. The
amplifier operates on + 27 Vdc.
3.3 Three-Stage Pre-Main Amplifier
The input of the amplifier uses three stages of class AB amplification, which provide
approximately 32 dB of gain in the 5 MHz band from 935 MHz to 940 MHz. The
amplifier operates on + 27 Vdc and a bias voltage of + 5 Vdc. The logic controls the +5
Vdc bias that shuts down the amplifier.
3.4 Main Amplifier
The signal provides approximately 11 dB of gain in the 935 MHz to 940 MHz frequency
band. The main amplifier operates on +27 Vdc, and a + 5 Vdc bias voltage. The alarm
logic controls the +5 Vdc bias voltage.
The main amplifier employs class AB amplification for maximum efficiency. The error
amplifier and feed forward loops are used to correct signal non-linearity introduced by
the class AB main amplifier. The error amplifier operates in a class AB mode. The RF
input signals are amplified 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 pre-main amplifier. The output from the pre-main amplifier is fed to the class AB
main amplifier.
The signal output from the main amplifier is sampled using a coupler. The sampled 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 continuously make adjustments to cancel out any
distortion in the final output signal.
3.5 Pre-Error and Error Amplifier
The pre-error and error amplifiers operate on +27 Vdc, and a +5 Vdc bias voltage. The
error amplifier applies approximately 30 dB of cancellation signal to the output of
the main amplifier.
3.6 Alarm Monitoring and Control
During routine operation, all normal variations are automatically compensated for by the
feed-forward loop control. However, when large variations occur beyond the adjustment
range of the loop control, a loop fault will occur. When this happens, the alarm LED will
illuminate RED on the front panel of the amplifier. The amplifier will be in the shut down
mode of operation. Reset of the amplifier is necessary for normal operation to resume.
