User's Manual

G3L-850-180 Cooling
044-05454 Rev A 1-4
The primary function of the second loop is to amplify the error signal to cancel out spurious products developed
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 second loop control section obtains a sample of the distortion added to the output signals by the main
a
mplifiers. 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 main amplifier output. The final output
is monitored by the second loop and adjusted to ensure that the signal distortion and intermodulation distortion
on the final output is cancelled out.
During routine operation, all normal variations are automatically compensated for by the feed-forward loop
c
ontrol. If large variations occur beyond the adjustment range of the loop control, the controller shuts down the
MCPA RF section and a loop fault is reported to the system.
Pilot Tone Generator
The pilot tone is an internally generated signal with a predetermined frequency, phase, and amplitude is known.
If the pilot signal is suppressed at the amplifier output, then the distortion created by the main amplifier is also
suppressed.
The pilot tone signal is injected into the first loop and detected at the feedforward output of the second loop. The
p
ilot tone is coupled off of the main amplifier creating a second pilot tone that is attenuated and phase shifted
180 degrees to be used as the reference. The second pilot tone is amplified in the error amplifier and mixed with
the signals from the main signal path.
The first and second pilot tones should cancel each other out in an ideal situation. If the output detector senses
th
at the pilot tones do not cancel each other out, the information feeds back to control the gain and phase of
both the main and error amplifier paths minimizing output distortion.
Controller
The controller constantly compares the active RF paths with internal references for dynamic correction of small
variations through the RF feedback control circuits to maintain constant gain, and also provides the alarm
monitoring and control for the MCPA.
A front panel mounted tri-color LED provides MCPA operational status to the local operator. The OFF/ON/
RE
SET switch allows the operator to power on, power off or reset the MCPA. System faults are sent to a remote
location through the user interface.
Cooling
The MCPA components are mounted on a heatsink and cooled by forced air flowing over the heatsink fins.
System fans draw external air through the MCPA front panel inlet and exhaust air through the MCPA rear panel
outlet. The internal temperature is monitored to keep the MCPA within the specified operating temperature.
Power Distribution
The host system provides +27 VDC power for the MCPA. The DC/DC converter and voltage regulator in the
MCPA converts the +27 VDC to +15 VDC, +9 VDC, +5 VDC, and -5 VDC for internal use. The MCPA has no
built-in short-circuit protection.
The MCPA operates at full power if the system DC supply is within 26 to 30 VDC. The MCPA shuts down if the
a
pplied DC power is less than 21.5 VDC or greater than 30.5 VDC.
Derating
MCPA RF power output is derated if the applied DC power drops below 26 VDC, but remains above 21.5 VDC.
RF output is reduced by 1.0 dB between 25 to 25.9 VDC, by 1.5 dB between 24 to 24.9 VDC and by 2.0 dB
between 21.5 to 23.9 VDC.