Comtech EF Data OM20 - Manual (Page 191)

OM20 Universal Outdoor Modem Appendix E
MN-OM20– Revision 5 E–9
E.7.3.1 Insert Terrestrial Frame Source
The Insert Terrestrial Frame Source selection tells the Modem from where the Insert Terrestrial
Frame is coming.
External: Indicates that the terrestrial frame is to be input via the Insert Data In Port
(Internally looped to the DDO Port).
Internal:
Indicates that the modem needs to generate the terrestrial frame and that all non-
inserted timeslots need to be filled with the appropriate idle code based upon the terrestrial
framing (T1 or E1).
The selection of the Insert Terrestrial Frame Source also influences the Buffer Clock selection in
the following manner:
When the Insert Terrestrial Frame Source selection is set to External, the received satellite data
will be clocked out of the Doppler Buffer based upon the clock recovered from the insert data
input. Therefore, the Buffer Clock selection will automatically be set to External and cannot be
modified. Attempts to select a different buffer clock will result in the error message INVALID
BUFFER CLOCK and the selection will not be allowed.
When the Insert Terrestrial Frame Source selection is set to Internal, the operator needs to
specify how data should be clocked out of the Doppler Buffer. In this case, the operator will be
able to select SCTE, SCT, RX SAT, or EXT EXC as the source for the Buffer Clock.
Therefore, the Insert Terrestrial Frame Source selection should be made prior to attempting to
change the Buffer Clock. In most instances, the Insert Terrestrial Frame Source selection will be
set to External and the Buffer Clock will automatically be set to External.
E.7.4 D&I Sample Configurations and D&I Clock Setup Options
The following are several examples of how to configure the modem for D&I. The OM20’s DDO
and IDI are internally looped
Example 1:
Drop 512 Kbps from a T1 trunk, 3/4 Rate Viterbi
Insert 512 Kbps into a T1 trunk, 3/4 Rate Viterbi
Drop 512 Kbps from a T1 trunk, 3/4 Rate Viterbi
Under Interface:
Under TX Setup
Set Tx Type according to your hardware configuration
(example: G703BT1B8ZS)
Under RX Setup
Set Rx Type according to your hardware configuration
Under Modulator:
Under Mod Data:
Set Data Rate = 512000
Set Conv Enc = 3/4 Rate VIT
Set Network Spec. = Drop & Insert