Comtech EF Data SDM-2020 - Manual (Page 118)

SDM-2020 Satellite Modulator Revision 7
ASI/RS-422 Data Interface MN/SDM2020M.IOM
9-3
A 75 Ω coaxial cable (Belden 8281 or equivalent) is recommended for all ASI connectors.
Typical coaxial cable length is up to 140 meters (460 feet) with good quality coaxial
cable. Typical attenuation of up to 18 dB at 270 MHz is permitted. The following cables,
or an equivalent computer grade cable incorporating twisted, shielded pairs, are
recommended for the RS-422 interface:
• Belden type LV Computer M9768
• Belden 8175
The Belden 8175 has a lower capacitance, however it has a larger diameter and requires
the selection of an appropriate connector shell. The typical cable length for the
serial/parallel interfaces is
≤ 5 meters (16.405 feet).
The interface operates to the specifications described in Table 9-1.
Table 9-1. ASI/RS-422 Specifications
General Specifications
Data Framing Formats 188, 204 byte packets per ETS 300 421, and None.
Hot Pluggable Not required. Unit power is turned off before removal or insertion of the
data interface.
ASI Specifications
Data Rate 1.5 to 100 Mbit/s ASI.
Clock Rate Uncertainty Programmed data rate ± 100 ppm.
Transport Clock ASI The transport rate is 270 Mbit/s for all data rates.
Impedance 75 Ω.
Return Loss 15 dB, frequencies, 5 to 270 MHz.
Loop Functions
(see Note 1)
Loopback
Loop Thru
Connectors BNC female, 75 Ω.
Electrical Properties Per TM 1449.
Packet Types Burst or distributed.
Signal Types Serial data.
Voltage Level 800 mV ± 10% into 75 Ω.
ASI Data Loop 3 dB Cutoff
Frequency
2 Hz
(see Note 2)
Jitter Tolerance Meets ITU-T G.823 (3/93) and ITU-T G.824 (3/93)
Jitter Transfer ≤ 0.5 dB peaking up to cutoff frequency.
–20 dB per decade beyond cutoff.
Cable Length, Typical
Rev. –
Rev. A RG59
50 m
100 m Belden 8281
70 m
140 m
RS-422 Specifications
Data Rate 1.5 to 18 Mbit/s, serial RS-422.
Clock Rate Uncertainty Programmed data rate ± 100 ppm.
Connectors 25-pin D female per EIA-530.
Electrical Properties Per RS-422.