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No Signal Strength

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Feb 23rd, 2008 at 1:12pm  
Hello all,

First I would like to say that is a great web site, I have used it many times before but this is my first time posting.  Ok, the problem is I had all of my equipment set up and had a BER of .000004-.000002 (93%Signal) but, the LinkStar modem kept dropping the link.  It was very random, it would stay linked for 5 or 6 days then drop the link, anywhere from 5 mins. to 3 to 4 hours.  Sometimes it was every other day.  I contacted Bentley Walker and the tech guys were very helpful but the only reason that we could come up with is, there is a set of power lines across the street that are interfering with the signal.  So I moved the dish, once the dish was moved i could not get anything stronger than 50% signal strength, so I moved it back to the original site, same problem.  I have checked and corrected for warping(was 4mm, now 0mm), and also checked the focal length as per Eric's instructions listed on this Website.  I think the focal length is off a little (ALOT).  After reading some post's I have began to believe that the intermittent service is because the BUC is going bad.  Nevertheless I still can not explain why I can only get 50% Signal Strength in the original location.  I have a Andrews 1.2M dish, good mount, 2 watt NJR BUC, NJR2784H LNB.  When I am aiming the dish I use a Horizon Digital Satellite Meter.  Also this is the Formula that I used for focal length 957.4mm=(1200mm*1200mm)/(16*94mm)
When I measure the focal length it appears to be over 1000mm.  I am going to put new RG6 ends on my coax and I have ordered a new LNB.  Any ideas???
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« Last Edit: Feb 23rd, 2008 at 3:10pm by N/A »  
 
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Eric Johnston
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Reply #1 - Feb 23rd, 2008 at 6:22pm  
You say that the link is dropped from time to time.  Are you saying that the receive BER goes very bad, like 0.1 from time to time and that the receive green LED goes out ?  If so, this suggests a bad contact in the LNB cable (quite likely), or less likely, an intermittent LNB fault or local interference.   It is not a good idea to have power cables passing through the beam to the satellite as this causes big sidelobes that may see adjacent satellites and thus receive and cause interference.

Your formula for focal length applies only to circular axi-symmetric dishes.  Offset dishes have a focal length which is the distance from the feed to the bottom edge of the dish.  If you are doubtful about your dish assembly send a picture of the side view.  eric@satsig.net    It is possible to incorrectly assemble some types of Andrew antennas, by putting the feed throat support yoke at the tip of the arm instead of near to the bend in the arm.

If you rework the LNB cable make sure the centre pin is clean and sticks out 2mm beyond the rim of the F plug.  When screwed in, the pin must go into the hole and not push back the cable itself.   If the outages are receive related try waggling the cables when the fault exists and see if you can get rx to go green again and thus diagnose the cause.    Do the outages occur at particular temperatures ?

If during 'dropping the link' your receive BER remains normal, then a transmit problem look possible.

If the problem seems transmit related, the two F connectors on the BUC cable are the most likely cause.

Next time you get an outage measure the receive BER several times.

The signal strength or signal level (as measured by a power meter) needs to be interpreted carefully.  The modem will operate perfectly with a wide range of signal strengths (from -30 dBm to -70 dBm) , provided the signal to noise ratio is good.   The signal strength (same as signal level) varies according to the length of the LNB cable.   The noise level also varies with the length of the LNB cable.

Regards, Eric.
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« Last Edit: Feb 24th, 2008 at 12:18am by Eric Johnston »  
 
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Reply #2 - Feb 23rd, 2008 at 9:09pm  
Eric,

When I say drops the link I mean the SAT light on the LinkStar modem goes from solid to a rapid flash.  Once it does this I can no longer telnet into the modem to get a BER reading.  I took a laser pointer and eyeballed the possible route the signal takes and it appears the signal passes over the power lines but not by much.  The feed throat is at the bend in the support arm.  The intermittent services is very very random, there is no pattern what so ever, sometimes night, sometimes day.  I will use great care when reworking the F connectors.  I can only assume that this equipment has been working in Iraq where the temp. can swing from 10-20F to 100-130F for about two years.  As far as the system working with a wide range of signal strength I do know that, I am at 52%(BER .000019-.000045) right now and posting this as I speak.  I was just wondering what would make it to where I could not reach the 90% that I was at before.  How would I measure the BER if I can not telnet into the modem when a link is not established?  I'm guessing I would use the IP address that I got from converting the MAC address on the back of the modem, because the one I use when the modem is linked is different.  Also the coax is 100FT I believe, and as soon as it goes down next which should be any minute I will try to telnet in with the converted IP.

Thank you much Eric.

Joseph
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« Last Edit: Feb 23rd, 2008 at 11:35pm by N/A »  
 
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Reply #3 - Feb 23rd, 2008 at 11:32pm  
Tried to telnet into the modem once it dropped the link but it would not let me... MSDOS just says connecting to..... then the IP address but then it times out.
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Eric Johnston
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Reply #4 - Feb 24th, 2008 at 12:15am  
It appears that the modem has rebooted itself.   The fast flashing green shows that it has successfully locked to the correct outlink carrier and it trying to connect with the hub.  If the modem has rebooted as a result of the hub commanding it then the hub should be able to help you.  If it has rebooted spontaneously then it looks like a modem fault or power supply interruption.

Either way it is not completing its commissioning sequence.  It could be a BUC transmit problem (attenuator set too high or too low) or burst timing error (lat and long wrong).   Have you told the hub your correct lat and long?.  Is your power setting correct?.

The modem IP address changes back to its default start up value, until commissioning is complete.

Explain this to the hub so they can watch your terminal from their end.  To make your PC compatible with the other IP address you need to change the PC gateway IP and its own IP address and its subnet mask.

Regards, Eric.
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Reply #5 - Feb 24th, 2008 at 2:53pm  
Eric,

I was able to telnet into the modem once the link was dropped. (had a brain fart on changing the computer IP configuration)  Any who this is what I got...

RSCorrectedErrorCount     65535    RSUncorrectedErrorCount   29345
    QPSKBER           0.00001939487    I2CErrorCount                 0
    LostSyncCount                 0    TimeSynced                87927
    MaxTimeSynced             87927    Synced                        1
    TimeUnSynced                  0    NCODeviation                  1
    CarrDeviation     -0.0001155543    VCOLocked                     0
    CodeRate                    5/6    CarrierPhase             LOCKED
    RSVit                    LOCKED    UCActive             NOT ACTIVE
    Rs                     27.50000    Fs                           85
    frequency                  1616    UCLoaded                      1
    RxPower               -38.02674    RSFrameLength              1424

BER 0.00001939487
    RSCorrectedErrorCount     65535    RSUncorrectedErrorCount   29345
    QPSKBER           0.00001939487    I2CErrorCount                 0
    LostSyncCount                 0    TimeSynced                87932
    MaxTimeSynced             87932    Synced                        1
    TimeUnSynced                  0    NCODeviation                 16
    CarrDeviation   -0.000006177685    VCOLocked                     0
    CodeRate                    5/6    CarrierPhase             LOCKED
    RSVit                    LOCKED    UCActive             NOT ACTIVE
    Rs                     27.50000    Fs                           85
    frequency                  1616    UCLoaded                      1
    RxPower               -38.02674    RSFrameLength              1424

BER 0.00001939487
    RSCorrectedErrorCount     65535    RSUncorrectedErrorCount   29345
    QPSKBER           0.00001939487    I2CErrorCount                 0
    LostSyncCount                 0    TimeSynced                87937
    MaxTimeSynced             87937    Synced                        1
    TimeUnSynced                  0    NCODeviation                -10
    CarrDeviation     -0.0002147141    VCOLocked                     0
    CodeRate                    5/6    CarrierPhase             LOCKED
    RSVit                    LOCKED    UCActive             NOT ACTIVE
    Rs                     27.50000    Fs                           85
    frequency                  1616    UCLoaded                      1
    RxPower               -38.02674    RSFrameLength              1424

BER 0.00001939487
    RSCorrectedErrorCount     65535    RSUncorrectedErrorCount   29345
    QPSKBER           0.00001454615    I2CErrorCount                 0
    LostSyncCount                 0    TimeSynced                87942
    MaxTimeSynced             87942    Synced                        1
    TimeUnSynced                  0    NCODeviation                 13
    CarrDeviation       0.002639693    VCOLocked                     0
    CodeRate                    5/6    CarrierPhase             LOCKED
    RSVit                    LOCKED    UCActive             NOT ACTIVE
    Rs                     27.50000    Fs                           85
    frequency                  1616    UCLoaded                      1
    RxPower               -38.02674    RSFrameLength              1424

BER 0.00001454615
    RSCorrectedErrorCount     65535    RSUncorrectedErrorCount   29345
    QPSKBER           0.00002909231    I2CErrorCount                 0
    LostSyncCount                 0    TimeSynced                87947
    MaxTimeSynced             87947    Synced                        1
    TimeUnSynced                  0    NCODeviation                -22
    CarrDeviation       0.002775998    VCOLocked                     0
    CodeRate                    5/6    CarrierPhase             LOCKED
    RSVit                    LOCKED    UCActive             NOT ACTIVE
    Rs                     27.50000    Fs                           85
    frequency                  1616    UCLoaded                      1
    RxPower               -38.02674    RSFrameLength              1424

BER 0.00002909231



Also I took a new Lat Long reading and will be E mailing it to Bentley Walker.  VSAT systems get passed around in Iraq so the original Lat Long could be off.

Also I would like to thank you for all of your help, keep up all the good work. 
Joseph
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« Last Edit: Feb 24th, 2008 at 4:28pm by N/A »  
 
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Reply #6 - Feb 24th, 2008 at 4:32pm  
Eric,

I just pulled the system information using the CONO command and as you can see here the modem is logging all of the TX Sync lost occurrences...
With this now in mind I do not think the modem is rebooting but I am thinking the Lat Long is very wrong, the TX cable ends are not making good connection or the BUC is getting ready to go out.  Also how far off does the Lat Long have to be off to cause problems?

TCM        Jan  1 00:00:01 :172 2007 Installed filter for MAC 1.0.5e.0.0.0
TCM        Jan  1 00:00:01 :172 2007 Installed filter for PID 869 (0x365)
TCM        Jan  1 00:00:01 :172 2007 Installed filter for PID 8188 (0x1ffc)
ETHER      Jan  1 00:00:01 :748 2007 Interface up at 100 Mbps Full duplex
LMFTPEXEC  Jan  1 00:00:05 :168 2007 Software will be stored in bank 0
LMFTPEXEC  Jan  1 00:00:05 :168 2007 Firmware will be stored in bank 1
TIMECLIENT Feb 24 13:34:42 :238 2008 Real time clock updated
TERMEXEC   Feb 24 13:34:43 :284 2008 Rx Synced
BBRCVR     Feb 24 13:35:12 :060 2008 Memdb updated from BB due to new Current Di
rectory
BWREP      Feb 24 13:35:12 :100 2008 Last burst dealloc delay set to 4s
TXACQSYNC  Feb 24 13:35:12 :202 2008 TXACQSYNC Initialized
TERMEXEC   Feb 24 13:35:41 :028 2008 NT sleep mode      DISABLED [17:45-18:00]
TERMEXEC   Feb 24 13:37:26 :196 2008 NCR Sync message received from TCL module
TERMEXEC   Feb 24 13:37:26 :196 2008 NCR Synced
TERMEXEC   Feb 24 13:38:39 :214 2008 Tx Synced
TTP        Feb 24 13:38:39 :216 2008 Enabled
TERMEXEC   Feb 24 13:38:39 :244 2008 NT sleep mode      DISABLED [00:00-00:00]
BBRCVR     Feb 24 13:38:39 :246 2008 CIR configured to be 0 bps
BBRCVR     Feb 24 13:38:39 :252 2008 Configuration Databases updated
IPQOS      Feb 24 13:38:40 :100 2008 BoD queue priority is just below queue #6
IPSA       Feb 24 13:38:40 :176 2008 IPHC : ENABLED (flags: 0x0)
IPSA       Feb 24 13:38:40 :176 2008 Del IP: 10.0.221.71 Net: 10.0.221.0
IFMGR      Feb 24 13:38:40 :178 2008 Add IP: 10.93.139.161 Net: 10.93.139.160
IPSA       Feb 24 13:38:40 :180 2008 Installed filter for PID 5902 (0x170e)
TERMEXEC   Feb 24 13:38:41 :024 2008 NT sleep mode      DISABLED [17:45-18:00]
TXACQSYNC  Feb 24 13:47:05 :150 2008 Tx Sync Lost (no corrections received)
TERMEXEC   Feb 24 13:47:05 :150 2008 Tx Sync Lost
TTP        Feb 24 13:47:05 :150 2008 Disabled
IPSA       Feb 24 13:47:05 :152 2008 Del IP: 10.93.139.161 Net: 10.93.139.160
IFMGR      Feb 24 13:47:05 :154 2008 Add IP: 10.0.221.71 Net: 10.0.221.0
TERMEXEC   Feb 24 13:48:23 :290 2008 Tx Synced
TTP        Feb 24 13:48:23 :290 2008 Enabled
IPSA       Feb 24 13:48:23 :292 2008 Del IP: 10.0.221.71 Net: 10.0.221.0
IFMGR      Feb 24 13:48:23 :296 2008 Add IP: 10.93.139.161 Net: 10.93.139.160
IPSA       Feb 24 13:48:23 :298 2008 Installed filter for PID 5902 (0x170e)
TXACQSYNC  Feb 24 13:49:34 :150 2008 Tx Sync Lost (no corrections received)
TERMEXEC   Feb 24 13:49:34 :150 2008 Tx Sync Lost
TTP        Feb 24 13:49:34 :150 2008 Disabled
IPSA       Feb 24 13:49:34 :152 2008 Del IP: 10.93.139.161 Net: 10.93.139.160
IFMGR      Feb 24 13:49:34 :154 2008 Add IP: 10.0.221.71 Net: 10.0.221.0
TERMEXEC   Feb 24 13:51:59 :508 2008 Tx Synced
TTP        Feb 24 13:51:59 :508 2008 Enabled
IPSA       Feb 24 13:51:59 :510 2008 Del IP: 10.0.221.71 Net: 10.0.221.0
IFMGR      Feb 24 13:51:59 :512 2008 Add IP: 10.93.139.161 Net: 10.93.139.160
IPSA       Feb 24 13:51:59 :514 2008 Installed filter for PID 5902 (0x170e)
TXACQSYNC  Feb 24 13:53:10 :368 2008 Tx Sync Lost (no corrections received)

Sorry for buggin you with all of this, I just really need the help of someone that can help me figure this out.  Thank you so much.

Joseph
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« Last Edit: Feb 24th, 2008 at 6:46pm by N/A »  
 
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Reply #7 - Feb 24th, 2008 at 7:49pm  
You need to send this info to your service provider for diagnosis.

If your lat and long are wrong in the hub database then your terminal will transmit at the wrong time and your transmit burst may arrive at the satellite at the same time as a burst from another site and thus overlap making it impossible for the hub to receive either burst.  Both sites then suffer failed transmissions.

The amount of lat/long error needed to cause problems depends on the direction of the error and the guard time allowed by the system designer between adjacent bursts.  If the error is sideways then little effect, if towards or away from the satellite then worse.  30 km error in range will produce 100 microseconds error in your receive clock timing and 200 microseconds error in your burst arrival time at the satellite.  

This page explains how a TDMA system works.  The educational example is very slow and has wastefully large guard times of 10000 microseconds, but you should get the idea that each site has to transmit at the correct time.

Equally, as you say, it could be the BUC cable connections or intermittent fault in the modem or BUC.  Connectors are a likely problem.

Regards, Eric.
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