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VSAT technology and installation >> LinkStar Forum: VSAT hubs and terminals >> Linkstar Modem : flashing LED ?

Message started by techtest on Aug 30th, 2009 at 5:14pm

Title: Linkstar Modem : flashing LED ?
Post by techtest on Aug 30th, 2009 at 5:14pm
Sir ,
I  have linkstar modem  which is working fine until 2 weeks ago .
Suddenly its started the problem of going down and SAT led is blinking. At that time checked and removed the LAN cable from modem, then by rebooting the modem its coming up.

We have checked the receiving signal and it is fine. Then we have changed BUC, LNB, feedhorn then also happening same problem.
Signal is good, we are using internet and it is going down. Its going down for 4 or 5 times a day.
Please help us out. Why its happening, what are the things we need to check ?

Title: Re: Linkstar Modem
Post by Forum Admin on Aug 30th, 2009 at 6:54pm
Just some questions to think about and some ideas.. Not sure about this...

Is it slow flashing or fast flashing ?  Does is stay the same flashing for a long time ?  Does it eventually go solid green (normal) ?.  Long time at fast flashing might be hub problem.   Does the SAT LED go off indicating loss of the outlink carrier ?   What is the QPSK BER before, during, after ?  

How do you reboot the modem ?  Do you cycle the power or type in a command ?  If you type in a command to get it back to normal you may have a hardware memory fault.

Does is always come up working normally after cycling the power ?

When you changed the LNB did the problem continue to occur ?  Sometimes the local oscillator in the LNB stops and cycling the power will restart it.  Often temperature related or sun angle on to the LNB.

Have you checked both ends of the LNB cable ?  The centre pin must be long enough and clean.  The outer braid sheath must connect to the plud outer shell at each end.

Is the power supply connected to the main circuit board with soldered wires or with a multiway plug?.  If it is a multiway plug, power everything off.  Earth your body to the chassis to avoid static electricity damage, and then unplug the plug and reinsert 5 times to clean the pins and spring contacts. Slightly low Vcc volts might cause such symptoms, due to slight corrosion on the plug contacts.  

Best regards, Eric.

Title: Re: Linkstar Modem
Post by techtest on Aug 30th, 2009 at 8:59pm
Sir ,
We have checked that it is fast flashing first and after some time slow flashing then Sat LED is becoming stable.
But it is taking long time to come up .
BER 0.0008824670—And we rebooted the modem by hard reboot ie . turning off and turning on the modem.
And after doing this reboot  by disconnecting the Ethernet cable it is coming up for sure.
After changing the LNB also it is happening again .We have checked the cabled and connected for moisture and everything and they are fine.
We have checked the power supply to modem and all they are fine.
So Sir, as final option do we need to change modem  or swap the cable ?
Also  Sir, sometimes I heard from some folks that swapping cables will help is that really helps us swapping ?


Title: Re: Linkstar Modem
Post by Eric Johnston on Aug 30th, 2009 at 10:16pm
I suggest you contact your hub and ask them to investigate why your site is having outages and is very slow to finally lock up after a power cycle.

It could be that your transmit carrier has poor quality at the hub.

I wonder if you could peak up your pointing to improve your receive QPSK BER.  Your present BER 0.00088 is satisfactory (but not good 0.0001, or excellent 0.00005 or less).  Your 0.00088 is quite feasible if your antenna is not well pointed and the satellite outlink carrier power rather high.  

Having an excessively high power outlink carrier makes it very easy for customers to find the satellite but makes it very difficult for them to comprehend that they still need to spend a lot more time peaking up properly to get the transmit pointing correct.

It really matters to get to the exact centre as the transmit beam is narrower then the receive beam, so you can have a perfectly satisfactory receive signal and still have a poor transmit signal.

It is no good the hub increasing your transmit power to try and compensate for your mispointing.  It will probably overload your BUC and cause signal distortion and poor signal quality into the hub.

I would get the hub to test your site using a CW carrier to check the P-1dB compression point and the quality of your bursts into the hub when the BUC power is at the P-1dB operating point. Then set the correct level.

Swapping the cables might identify if one cable has much more loss than the other.  Could the transmit cable be corroded internally with water ?  The transmit cable is very sensitive to losses as this directly affects the transmit signal.   The LNB cable loss may vary over a wide range (wanted signal level -30 dBm to -70 dBm, -50dBm typical) and the modem will compensate using automatic receive gain control,

Best regards, Eric.

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