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CDM-625 Advanced Satellite Modem
Introduction
0.0
0.1
0
-5
Comtech EF Data
CDM-625 Transmit
Power Spectral
-10
Density, referred to
symbol rate
-15
-20
-25
-30
-35
-40
-45
-50
Spectral
density, dB
-55
1.4.2
Demodulator
Note: Data rate range, operating modes, descrambling, input impedance/return loss etc, as per Sect. 1.4.1 Modulator.
Input power range,
desired carrier
Maximum Composite
Operating Level
Absolute Maximum,
No Damage
FEC
Adaptive Equalizer
Acquisition range
Acquisition time
Clock tracking range
Clocking modes
0.2
0.3
0.4
0.5
0.6
Intelsat
IESS
308/309
Tx Alpha = 0.25
Limit
950-2000 MHz (950-1950 MHz w/Firmware prior to Ver. 1.4.1) band:
-130 + 10
(symbol rate) to -80 + 10
log
50-180 MHz band:
-105 + 10
(symbol rate) to -70 + 10
log
950-2000 MHz band:
102 – 10 log(symbol rate, desired carrier) dBC, +10 dBm max, with the additional requirement that within ±10 MHz of the
desired carrier, composite power is ≤ +30 dBC.
50-180 MHz band:
94 – 10 log(symbol rate, desired carrier) dBC, +10 dBm max, with the additional requirement that
within ± 10 MHz of the desired carrier, composite power is ≤ +30 dBc
+20 dBm
Viterbi: 3 bit soft decision
Sequential: 2 bit soft decision
Trellis: Per IESS-310
Reed-Solomon(Open Network): Per IESS-308/309/310
Reed-Solomon(Closed Network): Proprietary
Turbo Product Codec: 6 bit soft decision, proprietary
LDPC: 5 bit soft decision, proprietary
VersaFEC: 6 bit soft decision, proprietary
5-tap design, selectable on/off
Programmable in 1kHz increments, and subject to the following:
Below 64 ksymbols/sec: ±1 to ± (Rs/2) kHz, where Rs = symbol rate in ksymbols/sec
Between 64 and 389 ksymbols/sec: ± 1 up to a maximum of ± 32kHz
Above 389 ksymbols/sec: ±1 to ± (0.1Rs) kHz, up to a maximum of ± 200 kHz
Highly dependent on data rate, FEC rate, and demodulator acquisition range.
Examples: 120 ms average at 64 kbps, R1/2 QPSK, ±10 kHz acquisition sweep range, 6dB Eb/No
2 s average at 18 kbps, R1/2 QPSK, ±10 kHz, 6dB Eb/No
Note: The use of Reed-Solomon, TPC, LDPC, VersaFEC increases acquisition time, due to the additional time taken for these
decoders to declare synchronization.
± 100 ppm min
Full range of clocking options supported – see plesiochronous/Doppler buffer section
0.7
0.8
0.9
1.0
1.1
Tx Alpha = 0.35
CDM-625
Modulator
typically < -50 dB, and
guaranteed to be
< -45 dB at offsets
> 0.75 Rs
(symbol rate) dBm
log
(symbol rate) dBm
log
1–16
MN-CDM625
1.2
1.3
1.4
1.5
Symbol Rate, Rs
Note: Tx Alpha = 0.25 requires
Firmware v1.4.0 or higher
Intelsat
IESS
308/309
Limit
Revision 13
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