(1) 4-Wire circuitry employing either 1600 or
connected to line isolators, which convert the 130 volt,
2600 Hz in-band signalling by using line amplifiers or
20- or 60-mA impulses into low-level 6-volt impulses.
pads and single frequency signalling units (SFSU) at
These are sent to the keyer to be converted into FSK
1600 Hz, 2600 Hz, or mixed.
signals, and then sent to the filter bridge unit. The
(2) 2-Wire circuit employing 20 Hz ringdown using the
received signals are sent to the isolators where they are
ringdown converter (RDC-4) and the termination set
converted back to 130-volt, 20-60 mA teletype impulses.
(4TS-2B). These modules occupy two of the line
(4) The five teletype circuits connected to the
conditioning shelves while the third shelf contains
VF TTY junction boxes are FSK and are routed through
redundant 1600 Hz and 2600 Hz signal supply units and
the TTY/FSK patch panel to the filter bridge unit which
a control-monitor panel for the 48 Vdc power supplies
combines all teletype circuits into one group to be
and 20 Hz ringing generator assembly.
connected directly to the VF patch panel for routing to a
reception. All teletype circuits appear at patch panels for
(1) The VF circuits are patched through the
ease of rerouting traffic, (5) The data circuits are
VF patch panel (fig. FO-4) which gives the operator the
connected from the entry panel through the data patch
ability to route the circuit through the system when the
are routed through the DATA patch panel to the modem.
(2) Four low-level teletype circuits may be
Orderwire. The orderwire provides terminal-to
connected to the keyers (transmit mode), which convert
terminal communications between operators.
the electrical impulses into frequency shift keying (FSK)
unique feature is the signalling tone for ringing. The
signals sent to the filter bridge unit.
orderwire is connected through the VF patch panel to the
During the receive mode, the signals from the filter
bridge are connected to the converters then sent out as
(3) Three high-level teletype circuits are
Section IV. AUXILIARY FUNCTIONS
6-12. Fault/Safety Alarm Monitor
c. Audible Signal Test. Placing the FAULT switch
The alarm monitor alerts terminal personnel to
equipment failures or safety hazards in either the radio
in the TEST position causes the audible alarm to sound.
audible alarm and visual indicators. The alarm monitor
6-13. Power Distribution
drawer includes a fault/safety gate, self-test circuits, and
a. Prime power to the terminal is three-phase,
a power supply.
four wire, 50/60 Hz + 5%, 120/208 Vac + 10%. Power is
a. Function. The alarm monitor receives fault
supplied by either of two 30-kW diesel-powered
input signals from the receive antenna control unit,
generator sets mounted on the power pallet. Manual no-
multiplex carrier group alarm, modem, power amplifier
break switchover between the on-line generator and the
(PA), CSS rack temperature, low antenna elevation
standby unit is accomplished by means of a generator-
(antenna safety cutoff switch), and waveguide alarms
paralleling switch and a transfer switch.
(waveguide proximity switches). The fault signal (high or
b. Three-phase ac power enters the terminal by
low) inputs are processed through the fault/safety gate.
two main feeder cables through the power entry panel
When a fault occurs, the alarm monitor sounds an
and EMI filters. From the power entry panel, the feeders
audible alarm and provides a visible signal on the front
are routed to the power distribution panel and four pole
panel. A modem fault will cause both the RSS and CSS
circuit breakers CB1 and CB2, MAIN POWER 1 and
alarm indicators to light.
MAIN POWER 2, respectively. These circuit breakers
Either a low antenna elevation or a waveguide fault will
control main power to the shelter. Main 1 supplies power
inhibit the high-voltage power supply.
to the radio subsystem, shelter lights and utility
b. Fault Override. The fault override switches on
the units give the operator a quick means of localizing a
dehydrator for the 20-foot antenna waveguide system.
fault from a general indication at the alarm monitor.
When the fault override switch on the fault unit is
and the air conditioners. A voltage trip module is on
operated, the audible alarm will be silenced, the alarm
each main to protect the equipment against prolonged
monitor fault indicator will extinguish, and the
undervoltage or over voltage conditions. The voltage trip
OVERRIDE indicator will light.
modules also monitor phase sequence and drive