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Pages: 1

Problem with Nera Satlink Modem

(Read 4346 times)
Ex Member
Ex Member

Mar 25th, 2008 at 12:16pm  
Dear Eric, All,

I 've a nera modem installed and the Rx and the Tx is locked, but there is no intenret link.

I checked with my Provider "Telenor", and they said we are not able to see you perfectly, note that my values is almost perfect, not that only, i am able to logon and establish a two way link, then how come they can't read my values.

Also when i type the command to show us the Rx valus most of the times this line appears with different values each time:

Viterbi Error Rate: 1.668 E-5 and some times it is higher? can that be the problem ?

I changed the BUC and LNB and Cables, Network Cables, everything except the modem coz i don't have a spare modem.

Also there is a C-Band antenna 2 m far from  the Ku Antenna, and no Walki Talki antenna and no GSM antenna.

I am confused if i am logged on and the two way link is established how come i am not able to receive internet?

My Satellite is Intelsat 1002 Spot 2 - Ku-Band
Find below my modem output:

# ip show
If       IPAddress      SubnetMask   BroadCastAddr   MTU  Alias AdminStatus
1  1500   eth0    1
2             N/A             N/A             N/A  4074   air0    1
3  4074   dvb0    1
Interface Statistics
   ------------- Input ----------------- ------------- Output
If    UCast   NUCast     Disc     Octets    UCast   NUCast     Disc   
1      123      119       11      25291        6       27        1      
2        0        0        0          0        0        0        0      
3        0        0        0          0      123        0        0    
IP  Receive  Deliver   Errors   Discards  Forward  Request  NoRoute 
       452       97      108          6      123       30        0      
Routing Table
      DestMask       RouteMask         NextHop  If   3   1   3

# dvb tx show

Satellite (DVB) TX Configuration
Auto start          : Disabled
Population ID       : 4
IDU output power    : -12 dBm
Default CW Frequency: 14.379000 GHz
AAL5 Encapsulation  : VC MUX

DVB Transmitter Status
State                 : On
IDU Output Power      : -12.2 dBm
Eb/No                 : 6.5 dB
delta T               : 248338 microseconds
Frequency Correction  : -110 Hz

# dvb rx show

Satellite (DVB) RX Configuration
Auto start          : Disabled
Frequency           : 11.606750 GHz
Symbol rate         : 13.356729 Msps

Satellite (DVB) RX Status
Rx State            : Forward link up
Frequency           : 11.609299 GHz
Symbol Rate         : 13.356700 Msps
FEC Code rate       : 7/8
SNR                 : 5.4 dB
Viterbi Error Rate  : 3.2663 E-4

# odu show

Antenna Configuration
Type                                Channel Master Type 184 - 1.8m
Tx Gain at 14.25 GHz                47.0dB

Transmitter (BUC) Configuration
Type                                JRC NJT5017F (14.0-14.5 GHz)
Local oscillator                    13.050000 GHz
24V DC supply                       On

Receiver (LNB) Configuration
Type                                Invacom SPV-1SM (10.70-12.75 GHz)
Local oscillator - High band        10.600000 GHz
Local oscillator - Low band         9.750000 GHz
Oscillator switching frequency      11.700000 GHz
LO Switching mode                   22kHz
13/18V DC supply                    13V

# sw show

SW versions
Boot                :
Current             :
Backup              :

Manual SW upgrade settings
TFTP server IP addr :
File name           : 1.tgz

Automatic SW upgrade settings
Activated           : No
PID                 : 511
IP address          :
Port No.            : 2001

Licenses for SW options
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IP Logged
Eric Johnston
YaBB Moderator

Posts: 2109
Reply #1 - Mar 26th, 2008 at 9:24am  
I suggest you send all this information to Telenor and ask for their help.

Your receive performance is bad ( SNR  : 5.4 dB  Viterbi Error Rate  : 3.2663 E-4 ).  You should see  Viterbi Error Rate of more like E-8 in clear sky conditions.
Try adjusting the pointing.  Alter the azimuth and elevation in small steps, like 1/2 turn of a nut, then measure the BER again and see what is the difference.  You may have to make perhaps 10 such adjustments and measurements and it may take 30 minutes to complete this task and get the beam exact centre.

If pointing does not solve the problem, check the polarisation angle.  You need to calculate it and set it to 1 deg rotation accuracy.  If you have this wrong you may be receiving interference from the opposite polarisation which is degrading your signal.   If the interfering signal varies from time to time then your BER may vary also.  Many carriers are intermittent.

Also consider the assembly of the dish/feed/feed arms arrangement.   Possible problems are that the feed yoke is not attached at the correct holes in the feed arm, side struts not attached at correct place, so out of focus?  Does it look right compared with the documentation pictures ?  Dish surface distorted?.  Do the crossed fishing line test.    If your dish has two short side struts at the rear, from the sides of the dish to the az.el head,  then they are there for a purpose - to prevent the sides of the dish being pulled forwards or pushed backwards by the weight of the BUC.  The inner end holes are elongated so you can tighten the nuts while a couple of other people pull on the sides of the dish. Adjust till the strings just touch.

You should be able to ping to IP addresses in the internet.  If you can do this but not access web sites by url name, then you have probably not set a valid DNS address in your PC.

Best regards, Eric.
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« Last Edit: Mar 26th, 2008 at 4:08pm by Eric Johnston »  
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Ex Member
Ex Member

Reply #2 - Mar 28th, 2008 at 2:14pm  
Dear Eric,

The problem was from the NOC, they didn't activate my account, however am still worried about:

1- Signal: I tried with my digital meter to get the best and to eleminate the message: Viterbi Error Rate as i didn't see it before on any nera terminals, but i faild, however the signal is 7.5 db which is good as the maximum i guess is 8.5 db, so baiscly increasing the signal wont remove the Viterbi Error Rate Message.

So i tried the plorization, if i turned the BUC left or to the right the singal goes down, so it is in the best position, i don't know how to remove the error message.

2- Electricity: Today when i touched the tripod i felt a small current and i couldn't keep holding the tripod, i don't know from where the current is, can it be from the connectors ?

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