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VSAT technology and installation >> LinkStar Forum: VSAT hubs and terminals >> 10 MHZ from RX port

Message started by JeffreyRDew on Aug 1st, 2012 at 4:52pm

Title: 10 MHZ from RX port
Post by JeffreyRDew on Aug 1st, 2012 at 4:52pm
Good day,
I'm trying to put together emergency fixes to a system. The Linkstar modem I have is an S2A. I require 10 MHz from the RX coax connector. I have only been able to find commands to transmit 10MHz to the BUC not to the LNB.

If anyone has run into this situation please let me know.

Title: Re: 10 MHZ from RX port
Post by Eric Johnston on Aug 1st, 2012 at 9:30pm
I'm not sure if that is possible.

At the command prompt try ? to get help.  A long list of all possible commands may be displayed. Do any commands look promising ?

If the modem is simply unable to send out a 10 MHz reference up the LNB cable then I suggest:
Use a different LNB with internal 10 MHz reference.
Use a 10 MHz reference from some suitable source and couple into the LNB cable.
Maybe even consider connecting a 10 MHz band pass filter incorporating a DC block between the TX and RX coax.

Please can anyone help with the proper answer ?

Best regards, Eric.

Title: Re: 10 MHZ from RX port
Post by JeffreyRDew on Aug 1st, 2012 at 10:40pm
Good Day Eric,
Thanks for replying. I see you answer many peopleís questions.

Iím in charge of several very poorly engineered systems. The modem is connected to a multiplexer where the 10 MHz is combined, at the antenna pedestal the 18v for the LNB is added. This 18v chip and the Multiplexer for the 10MHz have a tendency to fail. When I send the 18v from the modem, it gets cut off by the multiplexer. The only fix is to send both the 18v and 10MHz from the modem.

When these devices fail it tends to be a while before we can get new parts to the systems.

Iíve gone through the help file several times, but not all commands are in the help file.  Iíll keep trying different things :)

Title: Re: 10 MHZ from RX port
Post by Eric Johnston on Aug 2nd, 2012 at 12:52pm
General comments:

If you have a 1U shelf with 4 LNB power supply modules in a redundant array then it is important that there is good cooling. Put a fan shelf underneath to force cold air over it all the time.
Test the power modules from time to time to see if any have failed.

If you have redundant pair of 10 MHz oscillators, check that the power supply voltage regulators have been upgraded to latest modification. Switch between the two oscillators from time to time so you remain confident that both work.  If you power off the off line osc there should be no change in any of your network. If your network performance improves (Eb/No, BER..) then there is leakage from the off-line oscillator into the on-line 10 MHz distribution.    

If you have some cheap LNB power supply make certain that there is good smoothing.

If you connect a spectrum analyser (MUST HAVE DC BLOCK) to the LNB cable, look closely at the spectrum from 0 Hz to 2 MHz. There should be no spikes or noise due to the switch mode power supply.

For high reliabilty make sure LNB power supplies are kept cold.

For minimum phase noise, LNB power supply voltage regulation and smoothing is critical.

Best regards, Eric.

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