[time-nuts] have 10MHz need 19.5Mhz

Bob Camp lists at rtty.us
Sun Jun 2 20:28:52 UTC 2013


Hi

A SI5335 would appear to be a more straightforward way to get the 19.5 MHz. There are many other clock multiplier IC's out there. You don't need anything very fancy, just a divide by two on the input, a multiply by 39, and then a divide by 10. If the internal VCO will go to 400 MHz, you don't need the divide by two. Just do a X39 and a divide by 20. 

If you are doing some other logic "stuff" this sort of conversion is drop dead easy for the PLL's in most cheap FPGA's. Cyclone III(?), IV, and V will all do it no sweat. I *think* the switch from 20 MHz pll to 10 MHz was when they went from the II to the III. 

Bob

On Jun 2, 2013, at 2:59 PM, Chris Albertson <albertson.chris at gmail.com> wrote:

> 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
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.




More information about the Time-nuts_lists.febo.com mailing list