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Comtech EF Data CDM-QxL Multi-Channel L-Band Satellite Modem

The CDM-Qx and CDM-QxL are the first multi-channel satellite modems, with modular architecture that fit in a 1 RU chassis.
  • Forward Error Correction (FEC) Viterbi 1/2, 3/4, and 7/8 Concatenated Reed Solomon 1/2, 2/3, 3/4, and 7/8 Turbo Product Coding, IESS-315 Compliant (option)
  • BPSK, QPSK, 8-PSK and 16-QAM operation
  • Data Rate: 32 kbps to 20 Mbps
  • CDM-Qx: 50 to 90, 100 to 180 MHz CDM-QxL: 950 to 1950 MHz
  • Four slot chassis, allowing flexible configuration 1 or 2 modems. Up to 4 modulators. Up to 4 demodulators
  • DoubleTalk Carrier-in-Carrier bandwidth compression capability (option)
  • Interoperable with many Comtech EF Data satellite modems: CDM-550T, 570, 570L, 600, 600L, SDM-8000, 300A, and 300L3
  • Individual modulator output power control
  • Redundant Primary Power Supply (option)
  • High Stability Reference for CDM-Qx (option)
  • Common frequency reference for all modules
  • Asymmetric Loop Timing
  • Spectrum Analyzer Function
  • Enhanced D&I++ (option)
  • Automatic Uplink Power Control (AUPC)
  • Embedded Distant-end Monitor and Control (EDMAC)
  • Internal Redundancy (option) 1:1 modem 1:1, 1:2 or 1:3 modulator 1:1, 1:2 or 1:3 demodulator
  • SNMP, http and telnet for M&C
  • M&C Interface: EIA-232, EIA-485, 10/100BaseT Ethernet
  • Data Interface: EIA-422, V.35, Sync EIA-232, G.703 (E1/T1), and HSSI

CDM-Qx and CDM-QxL are also the first satellite modems to offer DoubleTalk™ Carrier-in-Carrier® bandwidth compression capability that allows the transmit and receive carriers of a full-duplex satellite link to be transmitted in the same transponder space, thereby providing a significant savings in leased bandwidth.

CDM-Qx and CDM-QxL with DoubleTalk Carrier-in-Carrier address common challenges encountered in satellite communications, including:

  • Reducing operating expenses (OPEX) for full-duplex links or increasing throughput or availability of full-duplex links without using additional transponder resources
  • Reducing capital expenses (CAPEX) by allowing a smaller BUC/HPA and/or antenna
  • Managing limited rack space


Figure 1 Without Doubletalk Carrier-in-Carrier

Figure 2 With Doubletalk Carrier-in-Carrier

Doubletalk Carrier-in-Carrier

Carrier-in-Carrier® is based on Applied Signal Technology's DoubleTalk™ bandwidth compression technology. DoubleTalk uses "Adaptive Cancellation", a patented technology that allows the transmit and receive carriers of a full-duplex satellite link to be transmitted in the same transponder space.

Available as an option, DoubleTalk Carrier-in-Carrier, when combined with advanced forward error correction and modulation techniques, can deliver unprecedented operating expense savings.

In addition to OPEX savings, DoubleTalk Carrier-in-Carrier can also provide CAPEX savings by allowing a smaller BUC/HPA and/or antenna.

Figure 1 shows the typical full-duplex satellite link, where the two carriers are adjacent to each other. Figure 2 shows the typical DoubleTalk Carrier-in-Carrier operation, where the two carriers are overlapping, thus sharing the same spectrum.

When observed over a spectrum analyzer, only the Composite is visible. Carrier 1 and Carrier 2 are shown in Figure 2 for reference only

Enhanced D&I++

The CDM-Qx and CDM-QxL support Comtech EF Data's proprietary closed network Drop & Insert (D&I++) for E1-CCS. The "n"x64 operation allows any value of "n" up to 31, and permits the simultaneous use of EDMAC and AUPC with minimal overhead. The D&I++ is interoperable with CDM-600/600L for "n" up to 24 (Viterbi and TPC FEC only).


The CDM-Qx and CDM-QxL support EDMAC, EDMAC-2, and AUPC. EDMAC/AUPC is compatible with CDM-600/600L and CDM-570/570L. EDMAC-2/AUPC is compatible with CDM-570/570L.

Turbo Product Coding

The CDM-Qx and CDM-QxL offer 2nd generation Turbo Product Codec (TPC) as an option. TPC provides increased coding gain while reducing the decoding delay, thereby leading to significant bandwidth savings. Following code rates are supported:

  • BPSK - 5/16 and 21/44
  • QPSK - 21/44, 3/4, 7/8, and 17/18
  • 8-PSK - 3/4, 7/8, and 17/18
  • 16-QAM - 3/4 and 7/8

Monitoring & Control

The CDM-Qx and CDM-QxL provide a range of options for local and remote management. The modem can be managed via the front panel, or the remote M&C port (EIA-232/EIA-485), or the 10/100BaseT Ethernet port. With support for SNMP, http and telnet, the modems can be easily integrated into an IP based management system.

Feature Enhancements

Enhancing the capability of CDM-Qx and CDM-QxL in the field is easy. Features that do not require additional hardware can be added on site, using FAST access codes purchased from Comtech EF Data. The FAST access codes can be entered from the modem front panel.

Data Interfaces

The CDM-Qx and CDM-QxL support a range of data interfaces - EIA-422, V.35, Sync EIA 232, and G.703 (T1/E1).

CDM-Qx Shown With:

Slot 1 - Modulator Card with G.703 Balanced Interface 
Slot 2 - Modulator Card with G.703 Balanced Interface 
Slot 3 - Modulator Card with EIA-530 Interface 
Slot 4 - Modulator Card with EIA-530 Interface 

  1. Also shown, placed above the CDM-Qx are the modulator and demodulator cards with G.703 Unbalanced (BNC) interface.
  2. Typically each modulator and demodulator card requires a data interface. However, if configured as a modem, only the demodulator card requires a data interface.