UNAOHM
40 EP2500 (Rev. 0)
9 DVB-S DVB-C DVB-T DEMODULATORS
9.1.1 QPSK Display Description
When the QPSK card is operating, the display shown on the screen is as follows, from top to bottom
(refer to Figure 19):
• The indication of the CH BER followed by the card status: LOCKED when the signal has been
locked, UNLOCKED when the parameters are not in the correct range of values and NO
CARRIER in the absence of an input signal
• The ANALOGUE BAR on the line below moves in a logarithmic scale to shows instantaneous
variations of the CH BER. This bar becomes longer from left to right in proportion to the better
quality of the signal as the BER decreases (improves). For a BER of 1E-2 (1 error out of 100) or
worse, the printing character of the BER readings become smaller. This limit is only indicative, the
decoder may still be operative although at its extreme limits. If the signal fails to be locked, the error
corrector receives chaotic data some of which casually coincide with correct data; and, as a result,
the BER does not reach 1, the maximum theoretical value, but values around 3 errors out of 10 (3E-
1). The bar also reflects this condition by failing to reset to zero completely.
• The indication of the post Viterbi BER (pV BER) which is always shown in smaller printing
characters to indicate the Channel BER is the most important parameter.
• Further below, is the number of uncorrected errors RU (from 0 to 65535), followed by the reading
of the amount of time taken to count the errors. The chronometer, like the RU error reading, is reset
to zero when the QPSK signal is unlocked.
• On the line below MER (Modulation Error ratio) of the digital channel is shown in dB. This
measurement too, is valid only when the carrier is locked.
• The “CFO” (Center Frequency Offset) indicates the difference between the nominal carrier
frequency and the effective operating value (as previously indicated, the demodulator is capable of
automatically tuning with accuracy, within ±3 MHz, to the programmed frequency). The CFO gives
a useful piece of information on possible frequency drifts of the “LNB” local oscillator.
• On the same line “PWR index” and a writing: OK, HIGH or LOW are shown. They indicates if
the signal has too high a level, or too low or just appropriate for the card to measure.
NOTE: The PWR index is only a response of the internal AGC (Automatic Gain Control) circuit of
the tuner. It indicates whether or not the level of the signal present on the tuner input is suitable for
digital decoding (this depends on both the programmed attenuation of the field strength meter and
the level of the signal available on the input.
The tuning frequency and the current program are shown on next line down.
SYMB for Symbol Rate with its value shown.
• CODE for Code Rate followed by its value. AUTO for automatic is also shown as the Code rate is
always automatically locked. On the same line M is shown to indicate the attenuation value
engaged.
•
SPECT on the bottom line tells of the polarity set followed by AUTO for automatic as the search is
done that way by the instrument.
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