Comcast LT1550-E Manuale utente
LT1550-E
www.comcast-sa.com
External modulate optical transmitter
LT1550-E
www.comcast-sa.com
Contenido
Safety Instruction...............................................................................................................................3
1. Overview ........................................................................................................................................5
1.1 About This Manual ...................................................................................................................5
1.2 Product Description..................................................................................................................5
6.2 Troubleshooting. ......................................................................................................................7
1.3 Product Applications ................................................................................................................8
2. Technique Parameters ...................................................................................................................9
2.1 Optical Parameters...................................................................................................................9
2.2 Model Test Indicators.............................................................................................................10
2.3 Test Condition ........................................................................................................................11
2.4 Technical Data Sheet ..............................................................................................................11
3. Panel Interface and Menu System Description ............................................................................13
3.1 Front Panel .............................................................................................................................13
3.1.1 Indicator Description...........................................................................................................14
3.2 Rear Panel ..............................................................................................................................15
3.3 Power Module............................................................................................................................15
3.3.1 220V Power Module........................................................................................................15
3.3.2 48V Power Module..........................................................................................................16
3.4 Menu Operation.....................................................................................................................16
3.4.1 Main Menu......................................................................................................................16
3.4.2 Display Menu...................................................................................................................17
3.4.3 Set Menu .........................................................................................................................19
3.4.4 Alarm Menu.....................................................................................................................21
3.4.5 AGC Mode .......................................................................................................................22
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3.4.6 MGC Mode ......................................................................................................................22
3.4.7 Frequency Adjust ITU in DWDM......................................................................................23
3.4.8 SBS Suppression Adjustment...........................................................................................23
4. Installing Optical Transmitter .......................................................................................................24
4.1 Receiving and Inspecting........................................................................................................24
4.2 Precautions.............................................................................................................................24
4.3 Mounting................................................................................................................................26
4.3.1 Mounting in the Rack ......................................................................................................26
4.3.2 Connecting the RF Cables ................................................................................................26
4.3.3 Connecting the Optical Fiber Cables................................................................................26
4.3.4 Connecting the Ethernet Cable........................................................................................28
4.3.5 Connecting Power ...........................................................................................................28
5. Communication Setup..................................................................................................................30
5.1 RS232 Communication Interface Description.........................................................................30
5.2 Set up the Hyper Terminal......................................................................................................30
5.3 Operating Parameters Configuration .....................................................................................34
5.4 Remote Monitoring: SNMP ....................................................................................................39
5.5 WEB Network Management...................................................................................................40
6. Maintenance and Troubleshooting ..............................................................................................44
6.1 Cleaning Fiber Optic Connectors ............................................................................................44
6.1.1 Cleaning Patch Cord or Pigtail Fiber Optical Connectors .................................................44
6.2 Troubleshooting .....................................................................................................................46
6.3 Disclaimer...............................................................................................................................48
Safety Instruction
LT1550-E
www.comcast-sa.com
LT1550-E
www.comcast-sa.com
1. Overview
1.1 About This Manual
This instruction manual is a complete guide to install and operate the (1RU)
LT1550-E series 1550nm external modulated optical transmitter. Please read
the entire manual before beginning installation.
This manual applies to LT1550-E series external modulated optical
transmitter.
• Chapter 1 gives general information about the LT1550-E series 1550nm
external modulated optical transmitter.
• Chapter 2 describes the complete technical specifications of LT1550-E.
• Chapter 3 describes the front/rear panel interfaces and menu system.
• Chapter 4 tells you how to install LT1550-E series external modulated optical
transmitter.
• Chapter 5 tells you the communication setting of LT1550-E.
• Chapter 6 describes maintenance and what to do in the event of problems.
1.2 Product Description
LT1550-E series optical transmitter is a 1550nm DFB laser external
modulated transmitter. It is specially developed for the CATV signal that
satisfies HFC network, and the long-distance transmission of cable phone and
cable data.
LT1550-E
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Working principle
LT1550-E series transmitter has 7 function modules: RF control, DFB laser,
optical modulator, SBS control, CSO control, communication/display control
and power supply.
Automatic gain control circuit (AGC) or manual gain control circuit (MGC)
amplifies the RF signal. AGC or MGC control makes the optical modulator
maintain a suitable input level. Use the detected RF root-meansquare(RMS)-
total power to calculate the optical modulation index(OMI).
In general we recommend using the AGC function, and special users can use
the MGC function to adjust the CNR/CSO/CTB performance indexes.
The core of transmitter is the optical modulator. The 1550nm signal input the
optical modulator, make the laser intensity changed follow the external RF
signal voltage, and then generate the AM optical signal.
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Stimulated Brillouin Scattering (SBS) occurs, when the optical input power is
greater than a certain threshold value. SBS generate the lower frequency
backscattered light which will attenuate the transmission light and return to
the laser while destroying its performance. Causing optical power fluctuation,
generates large noise, and seriously deteriorates the system carrier to noise
ratio (CNR). To improve the SBS threshold, LT1550-E series optical transmitter
adopts SBS control technology which is independent researched and
developed by ourselves. The threshold value can be set up to 19dBm.
The optical modulator has a two-way optical signal output. Parts of that signal
are routed to an InGaAs photodiode. This detection of the optical signal has
two functions:
1) Detect whether the laser is normal working. Once the output optical power
is 2dB lower than standard power, alarm will be set off.
2) Detect CSO distortion to optimize the bias point of the optical modulator.
For working normal the detector circuit needs at least two carrier signal inputs
with an interval of 24MHz. There is a CSO initialization program in the boot
process. If the CSO install failed, the RF indicator will flash red, see details in
6.2 Troubleshooting.
Block Diagram
LT1550-E
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1.3 Product Applications
• High-performance long-distance transmission
• High-power distribution network
• Redundancy loop architecture
• FTTx network
• RFOG application
• DWDM network
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2. Technique Parameters
2.1 Optical Parameters
Item
Unit
Value
Optical Wavelength
nm
1545～1560 (or specified by the
user)
Side-mode Suppression
ratio
dB
>30
Relative Intensity Noise
dB/Hz
<-160
Wavelength Adjustment
Range
GHz
+/-50GHz
Optical Power
dBm
2*7, 2*8, 2*9, 2*10
SBS Threshold Value
dBm
+13～+19 (Continuously
adjustable)
Laser Linewidth
MHz
0.3
LT1550-E
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2.2 Model Test Indicators
Test Model
C42
D59
D84
D84
Channel Plan
CENELEC42
PAL D59
PAL D84
PAL D
Channel Number
TV/FM/QAM64
42/0/0
59/0/0
84/0/0
30/0/48
Bandwidth Noise
5
5
5
5
CNR Tx/Rx
55.5
54.0
52.5
54.5
CNR Link 1
55.0
53.5
52.0
54.0
CNR Link 2
53.0
52.5
50.5
52.5
CNR Link 3
50.5
50.5
49.0
51.0
CSO Tx/Rx and Link 1
64
65
65
70
CSO Link 2
63
65
65
70
CSO Link 3
62
64
63
65
CTB
65
65
65
68
Indice
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