Doubletalk; Carrier- In-Carrier; (Cnc) - Comtech EF Data CDM-425 Installation And Operation Manual

1.4.5

DoubleTalk

Operating Mode
Power Spectral Density Ratio
and CnC Ratio
Maximum Symbol Rate Ratio
Inbound/Outbound frequency
uncertainty
Delay range
Eb/No Degradation
(equal Inbound/Outbound
power spectral density)
Monitor Functions
CnC Monitor Accuracy
Introduction
®

Carrier- in-Carrier

Requires the two links to share a common carrier frequency (Outbound and Inbound
symbol rates do not have to be equal)
BSPK/QPSK/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
3:1 (TX:RX or RX:TX)
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
0-330 ms
BPSK = 0.3dB QPSK = 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
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, 0.1 dB resolution
±0.2 dB for symmetric symbol rate
CDM-425 Advanced Satellite Modem
®

(CnC)

OQPSK = 0.3dB
1–27
Revision 0
MN-CDM-425