Comtech EF Data CDM-550T, Manual

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CDM-550T Satellite Modem Physical Description
Rev. 1.3 4–3
Rear Panel
External cables are attached to connectors on the rear panel of the CDM-550T. These
comprise the IEC line input connector, the Receive and Transmit IF connectors, the Data
connector, Alarms connector, Remote Control connector, and Auxiliary Serial connector.
The IEC line input connector contains the ON/OFF switch for the unit. It is also fitted
with two fuses - one each for line and neutral connections (or L1, L2, where appropriate).
These are contained within the body of the connector, behind a small plastic flap.
•
For 230 volt AC operation, use T0.5A, (slow-blow) 20mm fuses.
•
For 115 volt AC operation, use T1A fuses, (slow-blow) 20mm fuses.
FOR CONTINUED OPERATOR SAFETY, ALWAYS REPLACE THE FUSES
WITH THE CORRECT TYPE AND RATING.
The IF port connectors are both a 50 ohm BNC female type. 75 ohm cable connectors
(male) will have no problem mating with this 50 ohm type.
The Data connector is a 25 pin ‘D’ type female (DB25-F). This connector conforms to
the EIA 530 pinout, which allows for connection of different electrical standards,
including RS422, V.35, and RS232. Please note that it is the responsibility of the user to
provide the appropriate cables to connect to this EIA 530 connector. A shielded 25 pin
‘D’ type provides a very solid solution to EMC problems, unlike the sometimes used
V.35 Winchester connector. The pinout for the EIA 530 connector is provided in the next
section.
Note that the currently selected interface type is indicated by a small orange LED which
is located immediately above the connector. This provides an easy visual indication to
anyone mating a connector at the rear of the unit.
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 is also
provided which can mute the transmit carrier. This requires that the pin be shorted to
ground, or a TTL ‘low’, or an RS232 ‘high’ signal be applied.
As an aid to antenna pointing, or for driving step-track equipment, an analog AGC signal
is provided on a pin of this connector. The demodulator incorporates three separate AGC
control loops, one of which is analog, and two of which are entirely digital. The first of
these loops keeps the signal level constant at the input to the flash A/D converter in the
final IF stage. This loop has a limited dynamic range (~ 35 dB) and operates on the total
power within the IF bandwidth (which varies with data rate). The characteristics of this
control voltage are shown at the rear of the specifications section.