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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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