Tiernan DBR3000, Инструкция по установке и эксплуатации, Страница: 26 / 74

Theory of Operation
Indicator Color Description
modulator’s RF signal.
•
If the Rx Sync LED is green, the demodulator has “locked”.
•
If the Rx Sync LED is off, then the demodulator is not “locked”.
Signal Quality Red
Indicates the current received RF signal to noise ratio (defined as Eb/No) relative to
user-specified criteria. Refer to Table 2.3 for default values.
•
If the Signal Quality LED is solid Red, the Eb/No has dropped below the value set
by <Q0>.
•
If the Signal Quality LED is blinking Red, the Eb/No has dropped below the value
set by <Q1>, but is above the value set by <Q0>.
•
If the Signal Quality LED is off, the Eb/No is above below the value set by <Q1>.
Table 2.3 Signal Quality Defaults
Q0 = 4.0 dB; Q1 = 7.0 dB
Signal Level (Eb/No) Indicator
>7.0 dB Off
>4.0 dB, <7.0 dB Blinking Red
<4.0 dB or no RF Sync Red
2.2 Theory of Operation
The DBR operates in three FEC modes:
•
Sequential
o
Rates: 1/2 and 3/4 (ComStream)
•
Viterbi
o
Rates: Intelsat 1/2, DVB 1/2, DVB 2/3, DVB 3/4 DVB 5/6 and DVB 7/8
•
Viterbi and Reed-Solomon
•
Non-DVB (187/204 rate)
•
DVB (188/204 rate)
Sequential and Viterbi modes are “closed-network” modes. When operating in concatenated Viterbi and Reed-
Solomon FEC, the DBR offers two discrete operating modes: DVB and non-DVB.
Non-DVB mode forces the receiver to act as a data pipe: the receiver removes the synchronization pattern used
in the Reed-Solomon decoder from the output data stream and passed the 187-byte payload transparently to the
output.
DVB mode makes the receiver operate in compliance with the European DVB standard ETS 300 421, which
describes the transmission of audio/video programs encoded according to the MPEG-2 specification. In DVB
mode, the DBR expects the incoming data stream to be MPEG-2 transport packets. The 188-byte MPEG-2
transport packets provided at the output include the MPEG packet sync byte.
2-12 Tiernan DBR3000