Comtech EF Data CDM-Qx, Installation And Operation Manual

Page: 32 / 224

CDM-Qx Satellite Modem Revision 6
Functional Description MN/CDMQx.IOM
is enabled) where the overhead information is removed. Following this, the data passes to
the Plesiochronous/Doppler buffer, which has a programmable size, or alternatively
bypasses the buffer. From here, the receive clock and data signals are routed to the
terrestrial interface, and are passed to the externally connected DTE equipment.
Physically, a modem chassis is comprised of three main card assemblies:
•
The IF Backplane card includes the frequency reference, power splitters, power
summers, the FSK link (L-Band version only) and the IF Loop back functions.
•
The Digital Backplane card routes all the control signals, data path switching,
Carrier-in-Carrier
®
signals and power for all modules.
•
The M&C controls all functions in the unit.
Within the chassis are four slots which allow any combination of modulators or
demodulators to be installed. If configured as a single modem, two plug-in cards
comprising a modulator and demodulator are required.
•
A Modulator card contains the transmit interface circuits, the framer, the
encoder or encoders and the signal processing functions of modulation.
•
A Demodulator card performs all of the signal processing functions of carrier
search, cancellation, demodulation, Forward Error Correction, the de-framer,
plesiochronous/Doppler buffer and the receive interface circuits.
•
Terrestrial data interface cards can be on the modulator cards or demodulator
cards. When a modulator and demodulator are grouped together, the data interface
card can be used for full-duplex data interface. When one or up to four ports of E1
(with D&I) are needed, the Quad E1 Data Interface Module can be installed in
Slots 3 and 4.
Figure 3-1 shows a functional block diagram of the modem with either modulators and
demodulators in all four slots; and the figure also shows a modulator in Slot 1 and a
demodulator in Slot 2 along with a Quad E1 Data Interface Module in Slots 3 and 4.
3–2