Comtech EF Data CDM-700 - Manual (Page 134)

CDM-700 High Speed Satellite Modem Revision 5
Clock Modes MN/CDM700.IOM
8–2
Rx-Sat
Rx-Sat is the clock derived from the signal received from the satellite. It is the signal
sent from the distant end plus Doppler induced by the motion of the satellite.
Rx-Sat is the clock exiting the modem (RD or RT) when the Rx Buffer is disabled.
Rx Loop-Timed
In Rx Loop-Timed applications, ST is derived from the Rx-Sat clock. Depending
upon the interface, the Tx clock and Rx clock may be the same or different rates.
Buffer Enabled
When the Rx Buffer is enabled, one of several clocks is available to clock receive
data out of the modem and send the received data to the DTE, depending upon the
data interface. The Rx Buffer Clocks include Tx-Terr (TT or SD), Int Clk (derived
from Int Ref or Ext Ref) or Ext Clk. Some interfaces require the Tx = Rx data rate
and other allow Tx
≠ Rx.
Figure 8-1. Typical Data Interface (Features Vary By Interface)
The available clocking for each module is discussed in the sections that follow.
Rx Synth Rx Synth
Tx PLL Tx PLL
Tx PLL Tx PLL
Int Ref Int Ref
ST Synth ST Synth
Rx Buffer Rx Buffer
Ext Clk PLL Ext Clk PLL
Data Interface Card
Ext Clk
ST
TT
(or G.703 SD)
RT
(or G.703 RD)
Ext Ref
Tx-Sat
Rx-Sat
Int Clock
Rest Of Modem