Comtech EF Data CDM-Qx, Инструкция по установке и эксплуатации

Страница: 84 / 224

CDM-Qx Satellite Modem Revision 6
Front Panel Operation MN/CDMQx.IOM
A " display means that there are more channels beyond channel 6 as in this example.
Use right arrow key " to view more. Please make sure that the
ENTER
key is pressed
once it is done.
Selecting
Insert
displays the following submenu:
Port#X Rx Trib Rate:( ▲▼ ENT)
01536.000kbps (24x64kbps)
This is similar to the drop-side. Upon setting the data rate, a submenu displays as shown:
Px I-CH: 1 2 3 4 5 6 ►
TS: 11 02 06 04 05 03
This is similar to the drop-side except that this is done at the Rx side. Please make sure
that the
ENTER
key is pressed once it is done.
Selecting
LineCode
displays the following submenu:
Port#X Line Code:
HDB3 AMI ( ◄ ► ENT)
Select
HDB3
or
AMI
using the
! "
arrow keys, then press
ENTER
.
Selecting
Alarm
displays the following submenu:
Port#X Bipolar Violation:
Active Masked ( ◄ ► ENT)
Default is
Masked
.
5.7.1.7 (Config
%
Ref) - REFERENCE OSCILLATOR
The modem 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 modem actually phase locks to the reference external
signal. There are two distinct advantages to this scheme:
a. It permits hitless switching between the operation of internal and external reference.
There are no sudden discontinuities of frequency and phase in the transmitted carrier.
b. Due to the very low bandwidth of the PLL, it permits the external reference to have
an inferior phase noise characteristic than the internal reference of the modem. The
narrow loop essentially ‘cleans up’ the external signal. This is particularly important
if the modem is being used to supply a 10MHz reference to a BUC or LNB.
5–36