[time-nuts] Using a frequency synthesizer replacement for motherboard oscillator

Eric Garner garnere at gmail.com
Fri Nov 30 23:30:00 UTC 2012


the actual RTC on modern (Intel based) PC's is driven from a standard
32,768 Hz crystal attached to the PCH. some of them are in incredibly small
packages now instead of the old tuning fork-in-a-can ones. peeling off the
load caps and crystal from the board would allow you plenty of spaces to
tack down a lead from an external synthesizer.


-Eric

On Fri, Nov 30, 2012 at 3:04 PM, bownes <bownes at gmail.com> wrote:

> It all depends on what clock your talking about. Any given PC probably has
> more than one oscillator onboard.
> Generally there will be one for the CPU, one for the display circuitry,
> and probably one for the real time clock.
>
> Presuming you are talking about the CPU clock, it should be fairly
> straightforward to find the oscillator package on the motherboard find the
> pin with clock output and feed your clock input there.
>
> On Nov 30, 2012, at 16:59, Bob Camp <lists at rtty.us> wrote:
>
> > Hi
> >
> > It's most commonly done with things like a Soekris 45xx series board.
> You don't need anything very exotic for the frequency conversion. The
> jitter in the PC is way worse than what the external chips will be creating.
> >
> > The real question is - what is the "magic frequency" on the particular
> mother board you are going to modify? Once upon a time they all were a
> pretty predictable 14.xxx MHz. These days, who knows what's going in where…
> >
> > Bob
> >
> > On Nov 30, 2012, at 4:55 PM, Sarah White <kuzetsa at gmail.com> wrote:
> >
> >> Has anyone ever used a TAPR clock block or other frequency synthesizer
> >> to sort the clock drift / timing problems on a regular computer? I'll
> >> probably end up with a used dell or IBM workstation for this purpose.
> >>
> >> Recently, I came across a low-cost frequency synthesizer capable of
> >> using a 10mhz frequency reference (planning on using the thunderbolt
> >> GPSDO I'm working with once I manage to sort out the temperature issues)
> >>
> >> http://www.tapr.org/~n8ur/Clock-Block_Manual.pdf
> >>
> >> ^ TAPR "Clock Block" has an installation example for how to do what I'm
> >> planning with a Soekris net4501 low-cost / low-power embedded device...
> >>
> >> What I'm hoping to figure out is how to do the same, except on a proper
> >> computer such as the local used ones I'm able to get for less than $200
> >> with 2ghz with 30GB hard disk, 512mb or more ram, etc. So I figure this
> >> should be fine for what I'm planning.
> >>
> >> Example of what I'm trying to do, though based on the low-power embedded
> >> Soekris net4501 system from the TAPR manual's example section:
> >>
> >> http://www.febo.com/time-freq/ntp/soekris/index.html
> >>
> >> ^Aren't those the photos from clock block frequency synthesizer manual?
> >>
> >> Again, I'm wondering if anyone has opinions or experience about doing
> >> such things with NOT an embedded system (as I said, can get a nice 2ghz
> >> or so machine for less than $200 locally at a brick and mortar shop
> >> within walking distance)
> >>
> >> Thanks in advance,
> >> Sarah
> >>
> >>
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-- 
--Eric
_________________________________________
Eric Garner


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