Wavecom W40PC, Руководство пользователя

Страница: 60 / 264

52
•
General Operating Procedure WAVECOM Decoders v6.15 W40PC, W41PC, W51PC
BPSK has two phase shifts at +/- 180 degrees. For carrier recovery a Costas loop is used. A
Costas loop is a PLL with a special phase comparator which removes the payload data from
the PLL loop. Then the input signal is down-converted to base band by mixing the carrier in a
complex mixer, and the resulting signal is the data signal.
BPSK is almost exclusively used for satellite data links.
QPSK
Carrier recovery is mandatory to demodulate QPSK. As QPSK has phase shifts at +/- 45 and
+/- 135 degrees the signal must be squared two times to produce a carrier at four times the
original frequency. A PLL recovers the carrier in frequency and phase with ambiguities at +/-
90 and +/- 180 degrees. A complex mixer down-converts the signal to base band, and the
resulting signal is the data signal.
QPSK is almost exclusively used for satellite data links.
Options Menu
In the " Options " menu all support functions have been collected. This menu is also adapted to
each individual mode. Therefore the "Option" menu appears with very different contents. The
menu of the currently active mode is always displayed.
MSI
"
Multiple Scroll Inhibit
" (MSI) is a function which will suppress multiple linefeeds (LF). In
addition, a software generated Carriage Return (CR) is inserted when a carriage return is
received.
Using this menu item the function may be separately toggled on and off for the video output.
Using the MSI function has several advantages, e.g. when during reception disturbances a
carriage return character is lost, this software prevents lines being overwritten and text to be
lost. Some stations do not transmit carriage returns. The MSI function will then automatically
generate the missing carriage return. To clearly divide a message into paragraphs many
carriage returns are often transmitted.
Alphabet
The "
Alphabet
" menu at present has options for transparent and normal output. The normal
output includes fonts like: Latin , Greek , Cyrillic , Hebrew , Arabic etc.
ASCII characters for
German
,
Bulgarian, US
,
Swedish,Danish-Norwegian, Chinese
etc. output may be selected too.
Skyper , an alphabet which is used in POCSAG mode in Germany, is also available.