GA-123 High Frequency (HF) Modem

GA-123 HIGH FREQUENCY MODEM
Photos courtesy of the U.S. Marines and U.S. Navy
The DRS GA-123 High Frequency (HF) Modem guarantees HF
data interoperability across most modern modes of HF
communications. The system provides users with versatile
and flexible capability to ensure connectivity across the HF
spectrum and is suitable for ship and shore installations.
All modern electronics are contained on a single printed
circuit card.
The RS-485 multi-drop remote control has the capability to
allow multiple modems to be controlled from one remote
control facility.
Interfaces for user data, remote control, local control, radio
and power are provided. The user data interface, remote
control interface and radio interface all connect to individual
multi-pin connectors on the rear panel. The local control is a
Vacuum Fluorescent (VF)/Control assembly mounted to the
front panel. The GA-123 operates from 85 to 264 Vac, 47
to 440 Hz. A power cable is supplied.
The GA-123 is a Digital Signal Processing (DSP) hardware
engine and all firmware is in flash memory (Flash PROM).
Future enhancements are added to the GA-123 by
downloading new firmware via the remote control port
enabling enhancements to be added to GA-123 in the field.
The operating configuration is stored in non-volatile flash
memory so that the modem is automatically reconfigured
after power interruptions.
GA-123 HF Modem

HIGHLIGHTS
• Meets MIL-STD-188-110A, STANAG 4285 and STANAG
452 standards
• Programmable Frequency Shift Keying (FSK)
• Operator configurable data interfaces
• Local and remote control
• Continuous Wave (CW) interference suppression
• Full duplex
• Built-In-Test automatically on power up or operator initiated
RADIO INTERFACE
Transmit
Interface
Level
Keyline 1
Keyline 2
Receive
Interface
Dynamic range
Loopback
600 ohms
transformer coupled
Operator adjustable, -20 dBm to
+5 dBm, in 1 dB steps
+6 V = transmit (6 mA maximum),
0 V = no transmit
Open collector = no transmit
(+35 V maximum), 0 V = transmit
300 mA maximum)
600 ohms transformer coupled
-30 dBm to +5 dBm
Operator selectable audio loopback
CONTROL INTERFACES
Local control Front panel VF display (2 line by 16
character) keypad control
Remote control
EIA RS-232 ASCII serial interface
or RS-485 multi-drop
USER INTERFACE
Operation
User data rates
Coded
Uncoded
User data type
Full duplex (independent Tx/Rx
rates), half duplex (Tx precedence),
simplex
75, 150, 300, 600, 1200, bps
(110A, 4285 and 4529), 2400 bps
(110A and 4529)
1200, 2400, 3600 bps
(STANAG 4285) 600, 1200, 1800
bps (STANAG 4529), 4800 bps
(MILSTD-188-110A) 50, 75, 150,
300, 600 baud (FSK)
synchronous 110A, 4285 and
4529, asynchronous 110A, 4285
and 4529, 5, 6, 7 bit characters,
1.0, 1.5, 2.0 stop bits
User Tx clock source
User interface
Data sense
Clock polarity
Loopback
Internal (DCE supplied), external
(DTE supplied), clockless mode
Operator selectable, EIA RS-232,
RS-423, mixed mode
Controllable via front panel or
remote control
Controllable via front panel or
remote control
Operator selectable
digital loopback
SINGLE TONE MODULATION
Modulation types Single tone per STANAG 4285,
STANAG 4529, MIL-STD-188-110A,
programmable FSK
Modulation bandwidths 300