G3L-1929- Installation and Service Manual
4-4.3 Alarm Monitoring and Control
The alarm logic controls the +5 Vdc bias voltage that shuts down the amplifier. During routine op-
eration, 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 occurs. When this happens, an alarm indicator is illuminated on the front panel of the
subrack. The fault is transmitted back to an external summary module via the external alarm in-
terface connection on the front panel of the subrack.
4-4.4 First and Second Loop Control Circuits
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 first 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.
The second loop control section obtains a sample of the distortion added to the output signals by
the main amplifiers. The signal is phase shifted 180 degrees, then fed to the error amplifier where
it is amplified to the same power level as the input sample. The signal is then coupled to the error
signal of the main amplifier output. The final output is monitored by the second loop and adjusted
to ensure that the signal distortion and intermodulation distortion (IMD) on the final output is can-
celled out.
4-4.5 Pilot Tone Generator
The basic idea of injecting a pilot tone is that if the pilot signal is suppressed, then the distortion
from the main amplifier is also suppressed. To accomplish this, the pilot tone generator signal is
injected into the first loop and then detected at the feedforward output using the original pilot tone
as a reference. The information is then fed back to control the gain and phase such that the out-
put distortion is minimized.
4-5 Amplifier Module Cooling
The amplifier is cooled by forced air flowing over its heat sink, which is provided by two fans
mounted on the front of the subrack. The fans draw air through the front of the system and ex-
haust hot air out the back. The fans are field replaceable. Each amplifier, when properly cooled,
maintains the amplifier within the specified operating temperature range. Six inches of free space
are required at both the front and rear panels of the subrack to allow adequate air volume to cir-
culate over the heat sinks.
4-6 Power Distribution
Primary DC power for the amplifier is provided by the host system. The amplifier module has a
DC/DC converter and voltage regulator that converts the +27 Vdc to +15 Vdc, +5 Vdc, and -5 Vdc
for internal use.
Copyright Powerwave Technologies, Inc., May 2003. All rights reserved
044-05138 Rev. A
4-3
May 2003
