CiM-550 IP Enabled Satellite Modem

Rev. 2

Front Panel Menus

CD/CIM550.IOM

SELECT\CONFIG\RX\ACQ

 

DISPLAY

 

SELECTIONS/DESCRIPTION

 

 

 

 

 

 

 

The range is +/- 1 kHz to +/- 30 kHz.

 

EDIT RX ACQ SWEEP RANGE:

 

 

The value entered here determines the amount of

 

+/- 25 kHz (PRESS ENTER)

 

frequency uncertainty the demodulator will sweep

 

 

 

over in order to find and lock to an incoming carrier.

 

 

 

When operating at low bit rates, large values of

 

 

 

 

 

sweep range (compared to the data rate) will cause

 

 

 

excessively long acquisition times. For example:

 

 

 

selecting +/- 30 kHz with a data rate of 2.4 kbps,

 

 

 

BPSK, will result in an average acquisition time of

 

 

 

around 5 minutes.

SELECT\CONFIG\RX\DESCRAM

 

 

DISPLAY

 

SELECTIONS/DESCRIPTION

 

 

 

 

 

 

 

 

 

When Transparent mode is selected, a V.35

 

SELECT RX DE-SCRAMBLING:

 

 

descrambler is used. In Framed mode, a frame-

 

ON OFF

(PRESS ENTER)

 

synchronized descrambler is used. It is

 

 

recommended that scrambling/descrambling be

 

 

 

 

used at all times.

 

 

 

 

 

 

 

 

SELECT\CONFIG\RX\CLK

 

DISPLAY

 

SELECTIONS/DESCRIPTION

 

 

 

 

 

 

 

When OFF is selected, the Plesiochronous/Doppler

 

SELECT RX CLOCKING MODE:

 

 

buffer is disabled. The receive clock will then be

 

BUFFER ON OFF(PRESS ENT)

 

derived from the satellite signal, and will therefore

 

 

be subject to clock offsets relative to the local

 

 

 

transmit clock, and a small amount (< 5%) clock

 

 

 

 

 

jitter, due to the demodulation bit-timing recovery

 

 

 

process at low values of Eb/No.

 

 

 

When ON is selected, the Plesiochronous/Doppler

 

 

 

buffer is enabled. The input to the buffer will be the

 

 

 

signal from the satellite, with any clock offsets and

 

 

 

jitter. The output from the buffer will be derived from

 

 

 

the local TRANSMIT clock. In this way, the receive

 

 

 

data will be perfectly synchronous with this local

 

 

 

clock. The CiM-550 can be operated with

 

 

 

independent transmit receive and transmit data

 

 

 

rates. Even in this configuration, where RX data rate

 

 

 

<> TX data rate, the output clock for the buffer will

 

 

 

be phase locked to the transmit clock.

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