Comtech EF Data CDM-625A, Installation And Operation Manual

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CDM-625A Advanced Satellite Modem MN-CDM625A
Introduction Revision 4
1–23
1.4.5 DoubleTalk
®
Carrier- in-Carrier
®
(CnC)
Operating Mode
Requires the two links to share a common carrier frequency (Outbound and Inbound symbol rates do
not have to be equal)
Power Spectral Density Ratio and
CnC Ratio
BSPK/QPSK/8PSK/8-QAM: –7 dB to +11 dB (ratio of power spectral density, outbound interferer to
desired inbound)
16-QAM: –7 dB to +7 dB (ratio of power spectral density, outbound interferer to desired inbound)
Note: With asymmetric carriers, the absolute power ratio (or CnC ratio) would be different,
depending on the ratio of the symbol rates.
Example:
Outbound interferer = 1 Msymbols/sec
Desired Inbound = 500 ksymbols/sec
Ratio of power spectral density = +7 dB
Absolute power ratio
(CnC Ratio) = +7dB + (10 log Outbound/desired symbol rate) = +10 dB
Maximum Symbol Rate Ratio 3:1 (TX:RX or RX:TX)
Inbound/Outbound frequency
uncertainty
Within the normal acquisition range of the demod, as follows:
Below 64 ksymbols/sec: ±1 to ±(Rs/2) kHz, where Rs = symbol rate in ksymbols/sec
Between 64 and 389 ksymbols/sec: ±1up to a maximum of ±32kHz
Above 389 ksymbols/sec: ±1 to ±(0.1Rs) kHz, up to a maximum of ±200 kHz
Delay range 0-330 ms
Eb/No Degradation
(equal Inbound/Outbound power
spectral density)
BPSK = 0.3dB QPSK = 0.3dB OQPSK = 0.3dB
8PSK = 0.5dB 8-QAM = 0.4dB 16-QAM = 0.6dB
For +10 dB power spectral density ratio (outbound interferer 10 dB higher than desired inbound) add
an additional 0.3 dB
Monitor Functions Delay, in milliseconds
Frequency offset (between outbound interferer and desired inbound). 100 Hz resolution
CnC Power Ratio, in 0.1 dB (ratio of absolute power, outbound interferer to desired inbound)
Power Spectral Density Ratio, in 0.1 dB
CnC Monitor Accuracy ±0.2 dB for symmetric symbol rate