Radyne OM20 Specifications download pdf (Page 56)

OM20 Universal Outdoor Modem OM20 Theory of Operation

MN-OM20– Revision 5 4–18

4.11 OM20 Automatic Uplink Power Control (AUPC Operation)

Refer to Appendix F

4.12 Asynchronous Overhead Operation J3 (Framing/Multiplexer Capability)

The Asynchronous Framing/Multiplexer is capable of multiplexing a relatively low-speed

overhead channel onto the terrestrial data stream resulting in a slightly higher combined or

aggregate data rate through the modem. The overhead channel is recovered at the far end. This

added channel is termed variously “An Overhead Channel”, ”Service Channel”, “Async Channel”

or in IESS terminology an “ES to ES Data Channel.” The basic frame structure used by the

multiplexer is that specified in the IESS-309 Standard, resulting in a 16/15 Aggregate ratio of

overhead & data to data rates.

For Regular Async: (Standard IBS), the Baud Rate is approximately 1/2000 of the

Data Rate listed in Table 4-2.

For Enhanced Async: (IBS Async.), the Baud Rate is selectable, but Data Rate is

limited.

The maximum Baud Rate is 19,200 bps for IBS Async. Two software-controlled modes are

designed into the card to best utilize the available bits; “Standard IBS” and “IBS (Async)”. The

characteristics of the Channel Interface are also determined by the standard or Async mode.

The Async Channel can be set under software-control to either RS-232 or RS-485 mode. The pin

assignments for both modes are shown in Table 4-2.

The “RS-485” Setting controls the output into tri-state when the modem is not transmitting data,

allowing multiple modem outputs to be connected together.

Table 4-2.

Kbps Baud Rate Example for

Standard IBS

Kbps Baud Rate Example for

Enhanced Mode

128 64 9.6 300

256 128 19.2 600

384 192 32 600

512 256 64 1200

640 320 128 2400

768 384 192 4800

896 448 256 4800

1024 512 320 9600

1152 576 384 9600

1280 640 448 9600

1408 704 512 9600

1 2 ... 51 52 53 54 55 56 57 58 59 60 61 ... 219 220

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Radyne OM20 Specifications Page 56