# Crystal Reference Oscillator Design - RF Cafe Forums

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darcyrandall2004

Post subject: Crystal Reference Oscillator Design. Posted: Sun Oct 21, 2007 3:25 am

Colonel

Joined: Tue Feb 27, 2007 6:16 am

Posts: 46

Hello,

For the sake of learning and my own interest, I have been designing a UHF data radio.

Is this correct ?

If my carrier freq is 450.325MHz accurate to +/-200Hz

Lets say Im using a 20MHz Crystal reference oscillator for my PLL.

Then a rough calculation tells me that my crystal must be accurate to within -> 20*PPM*(450.325*10^6)/(20*10^6) < 200 -> 0.44PPM.

Where PPM is parts per million.

If these calculations are correct, can anyone recommend where I can find a crystal reference ocillator with a TTL or CMOS output, accurate to 0.44PPM? I believe an oscillator from 5MHz to 25MHz would be suitable.

FYI my channel width is 25kHz, Im using National's LMx2346. Thankyou

Regards Darcy Randall, Perth, Western Australia

_________________

Regards, Darcy Randall, Perth, Western Australia

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IR

Post subject: Posted: Sun Oct 21, 2007 5:14 am

Site Admin

Joined: Mon Jun 27, 2005 2:02 pm

Posts: 373

Location: Germany

Hello Darcy,

Your calculation is correct.

For such a tough spec as you have a simple Crystal is not good enough.

You should use a TCXO. I found an example for one with 0.28PPM and a CMOS output:

http://www.valpeyfisher.com/openlink.as ... FTX160.pdf

You can also ask for samples and define the frequeny that you need. Please contact the manufacturer for further help.

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darcyrandall2004

Post subject: Posted: Sun Oct 21, 2007 9:03 pm

Colonel

Joined: Tue Feb 27, 2007 6:16 am

Posts: 46

Legend. Thankyou

_________________

Regards, Darcy Randall, Perth, Western Australia

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