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Glossary
8PSK
8PSK
8PSK
8PSK: (8 Phase Shift Keying). This is the modulation type that is used for DVB-S2 also
called HD. In 8PSK, a symbol has 8 states or 3 bits. On the constellation diagram, an
8PSK signal either be “Normal”, with the eight points around a circle centred on the
origins or “Rotated” 22.5 degrees.
Attenuator:
Attenuator:
Attenuator:
Attenuator: The attenuator inserts an active resistance into the RF path and reduces the
signal level about 3 dB.
BER
BER
BER
BER: (Bit Error Ratio) This is the ratio of
Bits
Error
/ Bits
Received
This is a small number and is
usually expressed in scientific notation as BER = 2 X 10
-8
. Typically, BER should be smaller
than 1 X 10
-6
for good reception.
dB:
dB:
dB:
dB: (decibel) The decibel is a logarithmic ratio of voltage (or power) to a standard or
reference voltage (or power).
=
0
log
20
V
V
dB
or
=
0
log
10
P
P
dB
DiSEqC
DiSEqC
DiSEqC
DiSEqC: see Appendix D
DVB
DVB
DVB
DVB----S
S
S
S or DVB
DVB
DVB
DVB----S2:
S2:
S2:
S2: see Appendix C
FEC:
FEC:
FEC:
FEC: (Forward Error Correction) This is the error control used in DVB and other systems
to correct errors in transmission. To do this, the data is sent with additional error
correcting bits. On reception, the error bits are identified and (usually) corrected.
HD
HD
HD
HD:::: (high definition) This refers to any resolution above the DVB standard resolution.
The DVB standard resolutions for the luminance signal are (H X V):
720 X 576, 544 X 576, 480 X 576, 352 X 576, 352 X 288
The DVB-S2 High definition resolutions are (H X V) 1920 X 1080 or 1280 X 720. They
can either be interlaced or progressive. Interlaced means the picture is built from two
“fields” with each field being alternating half the scan lines. Progressive means the
entire picture is repeated each time. Progressive pictures require a higher data rate.
IF
IF
IF
IF: (intermediate frequency) This refers to the frequency after down conversion at the
LNB to the range 950 MHz to 2150 MHz.
IQ decision points
IQ decision points
IQ decision points
IQ decision points: During demodulation of a QPSK or 8PSK signal, the two phases of the
are converted to digital data and this data is sampled at the Symbol Rate. These samples
are called IQ decision points (as seen on the constellation diagram) and are then form
the digital input symbols.
LNB:
LNB:
LNB:
LNB: (Low Noise Block) The general name for the amplifier and downconverter at the
dish.
