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CDM-600L Satellite Modem
Physical Description
Overhead connector (P3A)
The Overhead connector is a 25-pin 'D' type male (DB25-M). It is used for passing
components of INTELSAT specified overhead frame structures. These include 64 kbps
RS-422 and 1/16 IBS overhead ESC at RS-232. The IDR backward alarm inputs are
found on this connector.
Audio connector (P4A)
The Audio connector is a 9-pin 'D' type female (DB9-F). It is used for the two 32 kbps
ADPCM audio inputs and outputs (600Ω transformer coupled, balanced signals). These
can be used for both ESC voice circuits in IDR mode, or as the primary data (FAST
option).
External clock connector (J9)
This is a BNC female connector. It is used for operating the buffer with an external
station clock. It requires an RS-422 compatible level, so this unbalanced input should
have a zero volt offset and a swing of at least ± 2V into the 120Ω termination provided.
IDR alarm connector (P5A)
The Alarms connector is a 15-pin 'D' type female (DB15-F). Four Form C backward
alarm outputs specified by INTELSAT are found on this connector.
External Reference connector (J12)
This 50Ω BNC female connector provides an external reference input for the Tx and Rx
IF synthesizers, and for the internal transmit clock. The load impedance is 60.4Ω, so the
VSWR is less than 1.25:1 at either 50Ω or 75Ω. Input level is 0 dBm minimum to +20
dBm maximum at 1, 2, 5, 10, or 20 MHz. When external reference is enabled, the
internal 10 MHz reference oscillator is phase locked to the external reference input by a
10Hz bandwidth PLL. If no activity is present at the external reference input, the modem
will revert to the internal 10 MHz reference.
Form C Traffic alarm connector (P5B)
The Alarms connector is a 15-pin 'D' type male (DB15-M). This provides the user with
access to the Form-C relay contacts, which indicate the fault status of the unit. These are
typically connected to an external fault monitoring system, often found in satellite earth
stations. In addition, the receive I and Q demodulator samples are provided on this
connector. Connecting these signals to an oscilloscope in X,Y mode will provide the
receive signal constellation diagram, which is a useful diagnostic aid. A pin also is
provided which can mute the transmit carrier. This requires that the pin be shorted to
ground, or a TTL 'low', or an RS-232 'high' signal be applied.
As an aid to antenna pointing, or for driving step-track equipment, an analog AGC signal
is provided on Pin 2 of this connector.
4–4
Revision 2
MN/CDM600L.IOM
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