RTU-292C Operations Manual
1-2
telephone set to be plugged into the rear panel of the RTU-292C; this local phone may then be
used in place of the unit's keypad and handset.
Input and output levels are internally adjustable to accommodate all types of radio systems. A
set-up mode allows the adjustment of the RTU-292C receiver and transmitter signal levels
without any external test equipment.
The unit will interface all types of two-wire lines, such as normal dial-up lines, dedicated lines,
or twisted-pair field wire. Although the output impedance is fixed at 600 Ohms, the adaptive
hybrid in the unit will give excellent hybrid balance regardless of the impedance of the line
connected to the unit.
The unit operates from an external AC power supply (provided) that operates from 90 to 270
VAC, 47 to 63 Hz, or from +12 or +24/+28 VDC nominal; the +12VDC range extends from +11
to +15 VDC, while the +24/+28 VDC range extends from +22 to +30 VDC. It is packaged in a
rugged enclosure measuring 3.5"H x 19"W x 12"D. All inputs and outputs, including those for
power, are filtered or protected as appropriate to enable the RTU-292C to meet the requirements
of FCC Part 15 rules for a Class A Digital Device.
1.3
ASSEMBLIES
The standard RTU-292C contains five PC board assemblies; the main board (with plug-on
adaptive hybrid DSP board), three front panel switch PC board assemblies, and the Options
Interface Board, which is mounted in the Options Tray where other option boards may be
installed. Mounted on the front panel along with the switchboards are a speaker, control
potentiometers, and handset jack. The various I/O connectors and the DC power input
connectors are accessible via the rear panel.
1.3.1
MAIN BOARD
The main board has six general sections of circuitry: The Telephone Interface Section,
Handset/Speaker Interface Section, Radio Interface Section, DSP Section, CPU Section, and
Power Supply Section. These are described briefly in the following paragraphs.
1.3.1.1
Telephone Interface
The Telephone Interface Section has the amplifiers that drive and receive audio from the phone
line. This section also contains the DSP hybrid, interfaced with the keypad. A tone ringer
generates a warble audio tone when ring voltage is received.
1.3.1.2
Handset/Speaker Interface
The Handset/Speaker Interface Section contains the speaker pre-amp and driver, the handset pre-
amp and driver. Audio gates controlled by the front panel switches route the audio to the speaker
and handset microphone preamplifier and ALC (Automatic Level Control) circuit.
1.3.1.3
Radio Interface
The Radio Interface Section consists of operational amplifier circuits that handle the audio
interfaces between the RTU-292C and the radio. The amplifiers provide gain adjustability to
accommodate various input and output levels, and also provide impedance transformation and
output drive capability. Audio gates controlled by the front panel switches and the CPU route
the audio as desired by the operator.
Summary of Contents for RTU-292C
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