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VSAT technology and installation >> LinkStar Forum: VSAT hubs and terminals >> 10 MHz Reference

Message started by abbas89 on Mar 16th, 2010 at 10:06am

Title: 10 MHz Reference
Post by abbas89 on Mar 16th, 2010 at 10:06am

Please explain me why we use 10 MHz reference for lnb and for buc and and why gps 10 MHz reference works and more stable than other ?

Looking forward

Title: Re: 10 MHz Reference
Post by Eric Johnston on Mar 16th, 2010 at 7:02pm
The 10 MHz frequency reference is used to phase lock the local oscillator in the LNB or BUC and thus make the local oscillator frerquency very stable.

LNB: If you are trying to receive small carriers or making measurements then high frequency accuracy in your LNB helps.

BUC: On transmit, frequency accuracy is essential so that you don't interfere with adjacent carriers and also in TDMA systems so that your carrier burst arrives at the hub at exactly the same frequency as the previous burst from someone else.

A 10 MHz reference may comprise an ovenised crystal oscillator (expensive) or an atomic (caesium or rhubidium) standard (very expensive).  Alternatively you can create a 10 MHz reference using a GPS receiver.  GPS satellites all have atomic clocks on board.

If you use a GPS derived frequency standard check what happens when you pull out the GPS antenna.  The GPS system suffers short outages when no satellites are visible and your system must be able to use a less accurate local reference for a while (e.g crystal).

Best regards, Eric.

Title: Re: 10 MHz Reference
Post by abbas89 on Mar 17th, 2010 at 6:51am
Thanks Mr.Eric for you instant and informative reply .

Best Regards,

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