[time-nuts] have 10MHz need 19.5Mhz

Chris Albertson albertson.chris at gmail.com
Sun Jun 2 18:59:09 UTC 2013


Recent talk about NTP servers.  It seems the limit to their accuracy is the
quality of the crystal that drives the CPU clock.  Most of them make really
good thermometers.  I'd like to try and replace the crystal on a Raspberry
Pi with a signal derived from a time nut quality 10MHz standard.

The Pi uses a crystal (not a TTL can, a real two lead crystal and a pair of
47pf caps) Both leads of the crystal attach to a pair of pins on an IC.   I
figure I can unsolder the crystal and inject a balanced 19.5MHz signal
directly to the IC's pins.    I know the ARM CPU just might work on a 20MHz
clock or maybe 15MHz but the video likely would not.  I'm going to have to
supply 19.5MHz.

The question is the best way to get from 10MHz to 19.5MHz.  I care only
about long term (tens of seconds to days) stability.

I thought of using an AD9850 DDS chip.   You can buy these on break out
boards very cheap on eBay but they need a 125MHz clock.    I could drive
the 9850 with a 120MHz clock that is multiplied up from 10MHz.    what is
the simplest 12x multiplier.   I assume getting to 125MHz from 10MHz is to
hard.

New-AD9850-module-modest-capacity-AD9851-DDS-Function-Generator-up-to-40MHZ<http://www.ebay.com/itm/New-AD9850-module-modest-capacity-AD9851-DDS-Function-Generator-up-to-40MHZ-/400422353936?pt=LH_DefaultDomain_0&hash=item5d3b083c10>


Is there a smarter and more direct way to get 19.5MHz for 10MHz?

-- 

Chris Albertson
Redondo Beach, California



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