Comtech-ef-data OM20 Bedienungsanleitung PDF herunterladen (Seite 50)

OM20 Universal Outdoor Modem OM20 Theory of Operation

MN-OM20– Revision 5 4–12

4.7 Clocking Options

The modem supports a number of different clocking options that can be recovered from the

satellite or the terrestrial links. The various clocking options allow users to determine which

clock will best fit their applications. Figure 4-7 gives an overview on how the modem processes

the various clocks for the Tx Clock source and the Rx Buffer Clock source. Tx and Rx Clocks

may be independently locked.

Tx CLK

SRC

High Stability

Oscillator

CLOCK

DATA

INTERNAL

SCT CLK

SRC

REF FREQ

SRC

SCT

SCTE

TRANSMIT

RECEIVE

CLOCK

DATA

RECOVERY

SCT

SCTE

RX SAT

SCR

BUFFER CLK

SRC

CLOCK

RECOVERY

IDI

MODULATION

HIGH STABILITY

DEMODULATION

CLK POL

DATA POLARITY

NORMAL

INVERTED

AUTO

INV

TERR

BASE

INVERT NONE

INV

BASEBAND

INV

TERR DATA

DATA POLARITY

BUFFER CLK POL

NORMAL

INVERTED

INV

TERR

BASE

INVERT NONE

INV

BASEBAND

INV

TERR DATA

Figure 4-7. Clocking and Polarity Diagram

4.7.1 TX Clock Options

TX clock options can be recovered from the terrestrial interface, satellite interface or internally

generated. The allows users to select SCTE Clock (Terrestrial) or the SCT internal clock. The

modem also allows user to recover the SCT Clock from the satellite (SCR) or from the modem

internally. The modem allows users to select clock polarity. The Tx clock selections available

are:

1 2 ... 45 46 47 48 49 50 51 52 53 54 55 ... 219 220

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