Comtech EF Data CDM-625 - Manual (Page 51)

CDM-625 Advanced Satellite Modem Revision 15
Introduction MN-CDM625
1–15
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
950-2000 MHz (950-1950 MHz w/Firmware prior to Ver. 1.4.1) band:
–130 + 10
log
(symbol rate) to –80 + 10
log
(symbol rate) dBm
50-180 MHz band:
–105 + 10
log
(symbol rate) to –70 + 10
log
(symbol rate) dBm
Maximum Composite
Operating Level
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
Absolute Maximum, No
Damage
+20 dBm
FEC
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
Adaptive Equalizer 5-tap design, selectable on/off
Acquisition range
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 max. of ±32kHz
Above 389 ksymbols/sec: ±1 to ±(0.1Rs) kHz, up to a max. of ±200 kHz
Acquisition time
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.
-55
-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5
CDM-625
Modulator
typically < -50 dB, and
guaranteed to be
< -45 dB at offsets
> 0.75 Rs
Comtech EF Data
CDM-625 Transmit
Power Spectral
Density, referred to
symbol rate
Symbol Rate, Rs
Spectral
density, dB
Intelsat
IESS
308/309
Limit
Intelsat
IESS
308/309
Limit
Tx Alpha = 0.35
Tx Alpha = 0.25
Note: Tx Alpha = 0.25 requires
Firmware v1.4.0 or higher