Data Interface: EIA-422, V.35, Sync EIA-232, G.703 T1, G.703 E1, Quad G.703 E1, G.703 E2 and
Enhanced D&I++ for Single & Quad E1
M&C: EIA-232, EIA-485, and 10/100Base-T Ethernet with SNMP, HTTP and Telnet support
Embedded Distant-end Monitor and Control (EDMAC)
Automatic Uplink Power Control (AUPC) Spectrum Analyzer Function
Asymmetric Loop Timing
Common frequency reference for all modules
Individual modulator output power control
CDM-QxL: 10 MHz reference for BUC, FSK communications and optional BUC power supply
CDM-QxL: 10 MHz reference and LNB power supply
Interoperable with many Comtech EF Data satellite modems: CDM-550T, 570, 570L, 600, 600L, SDM-8000, 300A, and 300L3
CDM-Qx Multi-Channel Satellite Modem
The CDM-Qx and CDM-QxL Multi-Channel Satellite Modems offer DoubleTalk® Carrier-in-Carrier®
bandwidth compression capability, allowing transmit and receive carriers of a full-duplex satellite link to
share the same transponder space. DoubleTalk Carrier-in-Carrier enables multi-dimensional optimization,
thereby allowing satellite communications users to:
Reduce operating expenses (OPEX)
Increase throughput without using additional transponder resources
Increase availability (margin) without using additional transponder resources
Reduce capital expenses (CAPEX) by allowing a smaller BUC/HPA and/or antenna
Or, a combination to meet specific user needs
Turbo Product Coding
The CDM-Qx/QxL offer 2nd generation Turbo Product Codec as an option. TPC provides increased coding gain with low decoding delay.
Combined with DoubleTalk Carrier-in-Carrier, they provide unprecedented savings in transponder bandwidth and power utilization as well
as earth station BUC/HPA size.
QUAD E1 Interface (QDI) with Enhanced D&I++
The CDM-Qx/QxL supports a Quad E1 interface that can aggregate up to four synchronous full or fractional E1s into a single carrier, with
very low overhead. This provides significant CAPEX savings by reducing the number of modems and the simultaneous reduction in
BUC/HPA size due to the elimination of multi-carrier backoff.
A proprietary, closed network Drop & Insert (D&I++) allows for Dropping or Inserting any combination of 1 to 31 Time Slots on each E1.
D&I++ is supported for E1-CCS only.
DoubleTalk Carrier-in-Carrier is based on patented bandwidth compression technology originally developed by Applied Signal
Technology, Inc. Using “Adaptive Cancellation” it allows transmit and receive carriers of a two-way link to share the same transponder
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
When observed on a spectrum analyzer, only the Composite is visible. Carrier 1 and Carrier 2 are shown in Figure 2 for reference only.
DoubleTalk Carrier-in-Carrier is complementary to all advances in modem technology, including advanced FEC and modulation
techniques. As these technologies approach theoretical limits of power and bandwidth efficiencies, DoubleTalk Carrier-in-Carrier utilizing
advanced signal processing techniques provides a new dimension in bandwidth efficiency.
DoubleTalk Carrier-in-Carrier allows satellite users to achieve spectral efficiencies (i.e. bps/Hz) that cannot be achieved with traditional
links. For example, DoubleTalk Carrier-in-Carrier when used with 16-QAM approaches the bandwidth efficiency of 256-QAM (8bps/Hz).
As DoubleTalk Carrier-in-Carrier allows equivalent spectral efficiency using a lower order Modulation and/or FEC Code, it can
simultaneously reduce CAPEX by allowing a smaller BUC/HPA and/or antenna.
DoubleTalk Carrier-in-Carrier can be used to save transponder bandwidth and/or transponder power thereby allowing successful
deployment in bandwidth-limited as well as power-limited scenarios. The following example illustrates the typical process for
implementing DoubleTalk Carrier-in-Carrier in a power-limited scenario:
The conventional link is using 8-PSK, TPC 3/4
Spread the signal by switching to a lower order modulation and/or FEC
code – say QPSK, TPC 7/8. This increases the total transponder
bandwidth, while reducing the total transponder power
Now using DoubleTalk Carrier-in-Carrier, the second QPSK, TPC 7/8 carrier can be moved over the first carrier – thereby reducing the
total transponder bandwidth and total transponder power when compared to the original side-by-side 8-PSK, TPC 3/4 carriers
EDMAC & AUPC
The CDM-Qx/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.
Monitoring & Control
The CDM-Qx/QxL provide a range of options for local and remote management. The modem can be managed via the front panel, the
remote M&C port (EIA-232/EIA-485), or the 10/100Base-T Ethernet port. With support for SNMP, HTTP and Telnet, the modems can be
easily integrated into an IP-based management system.
Enhancing the capability of CDM-Qx/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 CDM-Qx/QxL support a range of data interfaces – EIA-422, V.35, Sync EIA-232, G.703 T1, G.703 E1, Quad G.703 E1, G.703 E2
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
Also shown, placed above the CDM-Qx are the modulator and demodulator cards with G.703 Unbalanced (BNC) interface.
Typically each modulator and demodulator card requires a data interface. However, if configured as a modem, only the demodulator
card requires a data interface.
Unlike other data interfaces, the Quad E1 interface requires 2 slots in the CDM-Qx/QxL chassis
Data Rate (See Summary Table)
32 kbps to 20 Mbps, in 1 bps steps (data interface dependant)
Up to 10 Msps
V.35, or synchronous
FEC (See Summary Table)
Viterbi 1/2, 3/4 and 7/8 Concatenated Reed-Solomon 1/2, 2/3, 3/4, and 7/8
Turbo Product Coding
(TPC) - 2nd Generation
BPSK Rate 5/16 and 21/44 QPSK Rate 21/44, 3/4, 7/8, and 17/18 8-PSK Rate 3/4, 7/8, and 17/18 16-QAM Rate 3/4 and 7/8
EIA-232, EIA-485 (2- or 4-wire), 10/100 BaseT Ethernet with SNMP, HTTP and Telnet support
+76 - 10log(Symbol Rate) dBc within 10 MHz of desired carrier CDM-QxL: +87 - 10log(Symbol Rate) dBc (Broadband), +76 - 10log(Symbol Rate) dBc within 10 MHz of desired carrier, -5 dBm absolute maximum
CDM-Qx: ±1 to ± 32 kHz, programmable, in 1 kHz steps (Symbol Rate > 64 ksps) ±1 to ± (SR/2) kHz, programmable, in 1 kHz steps (Symbol Rate ≤ 64 ksps) CDM-QxL: ±1 to ± 200 kHz, programmable, in 1 kHz steps (Symbol Rate > 625 ksps) ±1 to ± 32 kHz, programmable, in 1 kHz steps (64 ksps < Symbol Rate < 625 ksps) ±1 to ± (SR/2) kHz, programmable, in 1 kHz steps (Symbol Rate ≤ 64 ksps)
512, 1024, 2048, 4096, 8182, or 16384 bits
Receive Clock Options
Rx Satellite, Tx Terrestrial, External Reference
± 100 ppm minimum
CDM-QxL: Off, 13 VDC or 18 VDC, 500 mA (max)
Minimum Symbol Rate
0 to 330 ms
Max Symbol Rate Ratio (See Whitepaper)
3:1 (Tx:Rx or Rx:Tx)
Max Power Ratio (See Whitepaper)
Tx Carrier Power (Interferer) – Rx Carrier Power (Desired), in dB, < 10 dB (except for 16-QAM, TPC, R=7/8) Tx Carrier Power (Interferer) – Rx Carrier Power (Desired), in dB, < 7 dB (16-QAM, TPC, R=7/8)
Satellite in “loop-back” mode (i.e. Tx station must be able to receive itself) “Non-processing” satellite (i.e. does not demodulate/remodulate the signal)