7
3.7 Loop Control Circuit
The primary function of the 1
st
loop is to provide an error signal for the 2
nd
loop. The
primary function of the 2
nd
loop is to amplify the error signal to cancel out spurious
products developed in the main amplifier. The input signal is amplified by a pre-amplifier
and fed to a coupler and delay line. The signal from the coupler is fed to the attenuator
and phase shifter in the 1
st
loop. The 1
st
loop control section phase shifts the main input
signal by 180 degrees and constantly monitors the output for correct phase and gain.
The 2
nd
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 on the main output signal. The final output is monitored
by the 2
nd
loop and adjusted to ensure that the signal distortion and intermodulation
distortion (IMD) on the final output is cancelled out.
3.8 Amplifier Module Cooling
Although each amplifier contains it own heat sinks, forced air is required for cooling the
heat sinks. This forced air-cooling pulls heat away from the heat sinks maintaining
optimum operation of the amplifiers. This ensures that the amplifier will operate to
specification across the specified operating temperature ranges.
3.9 Power Distribution
Primary DC power for the amplifier is provided by the host system. The amplifier has a
DC/DC converter and voltage regulator that converts the +27 Vdc to +15 Vdc, +12 Vdc,
and +5 Vdc, for internal use. +27 Vdc for the MCPA is supplied by the sub-rack,
through the D-subminiature connector on the rear of the MCPA.