Physical Interface; Operational Characteristics - GE DS-SD4-1 Reference Manual

MDS 05-4670A01, Rev. E

Physical Interface

The physical interface for analog operation utilizes pins on the radio's
(management) connector. This connector is multiplexed with the
COM1
serial data lines used for software commands. The applicable pins of the
DB-9 are as follows:
• Pin 4—Transmit Audio
(-20 dBm to 0 dBm, as set by TXLEVEL command)
• Pin 5—Ground (negative supply potential)
• Pin 6—Push-to-Talk (3 V TTL, 5 V tolerant)
• Pin 8—Receive Audio
(-20 dBm to 0 dBm, as set by RXLEVEL command)

Operational Characteristics

Analog operation is available in two general modes: Analog-only or
Mixed Analog/Digital.
Analog-only operation is typically useful when interfacing with external
analog modems. Operation is selected by specifying
this mode, RX and TX Audio are both always active; Carrier Detect
output and the LED are asserted based on the receiver
LINK
unsquelching. Key sources automatically assume the use of TX Audio
as the input source. In analog-only mode, carrier detect is based on
squelch status.
Mixed analog/digital operation is useful for orderwire application, or for
analog systems that need to make use of GE MDS Network-Wide Diag-
nostics. Operation is enabled by selecting a digital modem type (for
example, ) and selecting
MODEM 9600
is always active, but TX Audio only becomes active when the
Push-to-Talk (PTT, Pin 6) input signal is asserted. All other key sources
use digital modulation automatically. In this mode, Carrier Detect
output and the LED are asserted based only on detection of digital
LINK
modulation.
The PTT "asserted" condition is defined by the
Entering configures the system for an active high Push-to-Talk
PTTSIG HI
signal. Entering
PTTSIG LO
Push-to-Talk signal. Entering
input—useful for RX audio monitoring of the channel when no TX
analog transmission is desired.
Analog operating characteristics (selected either by PTT assertion or the
command) vary based on channel type.
MODEM NONE
As a simple rule, SD characteristics associated with
driven by the last digital modem selection. For example, if
is selected followed by
ation match the corresponding 12.5 kHz FCC/IC channel constraints. If
SD Series Reference Manual (x710 Mode)
AUDIO ON
configures the system for an active low
disables the Push-to-Talk
PTTSIG OFF
, the characteristics for analog oper-
MODEM NONE
. In
MODEM NONE
. In this mode RX Audio
command.
PTTSIG
are
MODEM NONE
MODEM 9600
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