Comtech EF Data CDM-570 - Manual (Page 117)

CDM-570/570L Satellite Modem with Optional IP Module Revision 12
Front Panel Operation MN/CDM570L.IOM
5–31
5.2.2.1.8 CONFIG: Ref (Reference)
IMPORTANT NOTE: The CDM-570/570L can accept an externally supplied
frequency reference, using the BNC connector on the rear panel. However, rather
than bypassing the internal reference, and substituting the external signal, the
internal reference is used in a low-bandwidth (~ 2Hz) phase-locked loop (PLL), so
the CDM-570/570L actually phase locks to the reference external signal. There are
two distinct advantages to this scheme:
1. This scheme permits hitless switching between the operation of internal and
external reference. There are no sudden discontinuities of frequency and
phase in the transmitted carrier.
2. Due to the very low bandwidth of the PLL, this scheme permits the external
reference to have an inferior phase noise characteristic than the internal
reference of the CDM-570/570L. The narrow loop essentially ‘cleans up’ the
external signal. This is particularly important if the CDM-570L is being used to
supply a 10MHz reference to a BUC or LNB.
Use the ▲▼arrow keys to edit the configuration and value of the frequency reference – values of
Internal 10 MHz, External 01 MHz, External 02 MHz, External 05 MHz, External 10 MHz,
and External 20 MHz are available – and then press ENTER when done. For example:
Frequency Reference:
Internal 10 MHz(▲ ▼,ENT)
Frequency Reference:
Internal 05 MHz(▲ ▼,ENT)
5.2.2.1.9 CONFIG: Mask
Alarm Mask: Transmit
Receive Ref BUC LNB (◄ ►)
Use the ◄ ► arrow keys to select Transmit, Receive, Reference, BUC (CDM-570L only), or
LNB (CDM-570L only), and then press ENTER.
5.2.2.1.9.1 (CONFIG: Alarm Mask) Transmit
Tx Alarm Mask: Tx-FIFO
G703BPV TxAIS G703LOS ◄ ►
Use the ◄ ► arrow keys to select Tx-FIFO, G703BPV, Tx-AIS, or G703LOS, and then press
ENTER.
Each choice displays a submenu similar to the TX-FIFO submenu:
Tx-FIFO Alarm:
Active Masked (◄ ►,ENT)
Use the ◄ ► arrow keys to select Active or Masked, and then press ENTER.