LEARNING EVENT 34: BASEBAND AMPLIFIER
1. The baseband signal, which is the demodulated output from the phase detector in the demodulator section, is
coupled to the baseband amplifier section where it passes through one of seven gain-adjust potentiometers. The
gain-adjust potentiometers provide preset gain for the different modes of operation. The baseband signal is fed
through one of these potentiometers, which is selected according to the mode of operation, to the baseband
2. The feedback-pair amplifier is a wideband amplifier with a 75-ohm output that is essentially flat from 300
Hz to 500 kHz. This wideband output is not now being used but is available for future use.
3. Buffer amplifier G2 is a baseband amplifier that accommodates 12 to 60 voice channels. It has a 75-ohm
output with a frequency response of 300 Hz to 252 kHz. Amplitude reduction of the input signal's HF
components applied to this amplifier is provided by one of three selectable deemphasis filters. The broadband
75-ohm output is not currently used but is available for future multiple access use.
4. Buffer amplifier G3 is the normal baseband amplifier and has a 600-ohm balanced output with a frequency
response of 300 Hz to 20 kHz. This amplifier's input is deemphasized by the deemphasis filter. The output of
this amplifier is coupled to the baseband patch panel in the terminal equipment. This output accommodates
from one to five voice channels.
LEARNING EVENT 35: MONITORS AND CONTROL CIRCUITS
1. Meters and indicator lights are used to monitor AGC voltages, AFC-sweep voltages, voltage outputs from
power supplies, baseband output levels, and threshold margin levels. Carrier loss and carrier lock-on signals
from the equalizer and frequency control unit are coupled to the receiver control circuits. These signals are fed
to indicator lamps to indicate whether or not the receiver is locked onto the received signals.
2. The nine mode-select signals from the receiver control circuits are distributed to various modules in the
receiver. These mode-select signals are applied through OR gates to the designated receiver circuits.
3. The receiver control circuits, consisting of indicators and selector switches, are located on a remote control
panel. The remote control panel contains nine electrically interlocked mode selector switches, four electric
interlocked satellite channel selector switches, a carrier loss/lock-on indicator, and a threshold margin meter.