Comtech EF Data DMD-2050E - Manual (Page 90)

DMD2050E Universal Satellite Modem Theory of Operation
MN-DMD2050E Revision 2 3–48
3.11.13 DoubleTalk Carrier-in-Carrier Specifications
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/8-PSK/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 32 ksymbols/sec: ±1 to ± (Rs/2) kHz, where Rs = symbol rate in
ksymbols/sec
Between 32 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
8-PSK = 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 ratio, in dB (ratio of absolute power, outbound interferer to desired
inbound)