Extended Temperature Option; Direct Sequence Spread Spectrum (Dsss) Option - Comtech EF Data SLM-5650A Installation And Operation Manual

1.3.1.7.2

Extended Temperature Option

Extended temperature range is -32 to 50°C. When operating from -32 to 0°C (the Network
Processor option range is -25 to 50°C), Tx power accuracy is ∀1.5 dB. A heater is installed on the
bottom of the chassis. This 300-Watt heater operates at 120 or 240 VAC.
When temperatures are below 0°C, a 10-minute warm up period is required upon power-up
before the modem boots. Comtech EF Data recommends that you allow an additional 15 minutes,
for a total of 25 minutes of recommended warm-up time, to ensure performance to specifications.
1.3.1.7.3

Direct Sequence Spread Spectrum (DSSS) Option

DSSS operation over WGS and DSCS has not been ARSTRAT approved.
As On-The-Move systems with very small dishes (e.g., VSATs) become more popular, there is an
increased interest in Spectrum Spreading. To meet this need, DSSS is optionally available in the
SLM-5650A.
DSSS works by modulating the normal carrier with a pseudo-random PN sequence (chips) at a
much higher chip rate. The chip rate is determined by the carrier's symbol rate and a multiplying
(spreading) factor.
The SLM-5650A offers spreading in the following LDPC MODCODs:
•
LDPC ULL BPSK 1/2
•
LPDC LL BPSK .378
•
LPDC LL BPSK .451
•
LPDC LL BPSK .541
•
LDPF HP BPSK 1/2
The Spreading Factors currently supported are 1 (Spreading Off), 2 through 512 up to a
maximum chip rate of 23 Mcps. You can select between four built-in pseudo-random PN
sequences so that multiple spread carriers can occupy the same bandwidth in a Code-Division
Multiple Access (CDMA) fashion.
When using large spreading factors, the SLM-5650A also exhibits a large tolerance to jamming –
up to 24 dB – and a Low Probability of Detection and Interception. With DSSS enabled, the lower
data rate limit has been reduced to 8 kbps.
The SLM-5650A Base Modem Web Server Interface provides a Web page to facilitate anti-
jamming applications. This page allows you to configure the modem parameters so that a fixed
occupied bandwidth can be maintained.
Lastly, there is no loss in performance with spreading enabled.
Introduction 1–10
SLM-5650A Satellite Modem
Revision 10
MN-SLM-5650A