[time-nuts] 10MHz to 25MHz

[Scott Stobbe]

Is there any reason why you wouldn't be able to run the same drive level on
say the fifth overtone versus the fundamental? I would guess at 100 MHz it
may be 3rd or 5th, or are they fundamental?

The comments one drivelevel are simply based on snr, larger signal with
same noise, better snr

On Thu, Jan 19, 2017 at 7:06 PM Bob Camp <kb8tq at n1k.org> wrote:

> Hi
>
>
>
>
>
> > On Jan 19, 2017, at 3:03 PM, Scott Stobbe <scott.j.stobbe at gmail.com>
> wrote:
>
> >
>
> > Wouldn't crystal drive level be one of the important specifications for
> far
>
> > out phase noise?
>
>
>
> It would, but you can get the same floor at 10 MHz as you can get at 100
> MHz.
>
>
>
> Bob
>
>
>
> >
>
> > On Thu, Jan 19, 2017 at 1:33 PM, Bob Camp <kb8tq at n1k.org> wrote:
>
> >
>
> >> HI
>
> >>
>
> >> A lot of your evaluation of the term “better” will depend on your
> intended
>
> >> use. One of the limits on phase noise
>
> >> is the thermal noise floor. Because of that, starting at a higher
>
> >> frequency will always give you an edge on broadband
>
> >> phase noise. ADEV / short term stability is linked to the Q of your
>
> >> resonator. In a quartz crystal, maximum Q is
>
> >> roughly proportional to frequency. The other limit on Q is blank
> geometry
>
> >> (size). One other limit is practicality -
>
> >> is a $250,000 OCXO that is 1 cubic meter in size appropriate for your
>
> >> application? The answer to that one is
>
> >> universally - NO :) Somewhere along the line of larger size and cost,
>
> >> other technologies make more sense.
>
> >>
>
> >> So, if better = phase noise floor, 100 MHz is better than 10 MHz. If
>
> >> better = ADEV, 5 MHz in a large package is
>
> >> likely better than 100 MHz. Indeed these are only two variables. There
> are
>
> >> *many* others you could look at.
>
> >>
>
> >> Lots of fun
>
> >>
>
> >> Bob
>
> >>
>
> >>
>
> >>
>
> >>> On Jan 19, 2017, at 7:13 AM, Charles Steinmetz <csteinmetz at yandex.com>
>
> >> wrote:
>
> >>>
>
> >>> Chris wrote:
>
> >>>
>
> >>>> I have always wondered why we build our "standard" with such a low
>
> >>>> frequency.   Why not a 100MHz GPSDO?   Why 10MHz
>
> >>>
>
> >>> Quartz crystals work better at lower frequencies, predominantly because
>
> >> they have higher Q.  10MHz was chosen because it is low enough for
>
> >> excellent performance but high enough to be directly useful (since an
>
> >> accident of biology gave us ten fingers, we've created a base-10 world
> and
>
> >> powers of 10 are favored in almost everything).
>
> >>>
>
> >>> In prior times, 5MHz crystals held this position, and before that,
>
> >> 1MHz.  There is a good argument even today that the best 2.5MHz or 5MHz
>
> >> crystals are better than the best 10MHz crystals, but not by enough to
> make
>
> >> 2.5MHz or 5MHz standards popular any longer.
>
> >>>
>
> >>> One lonely data point, which proves nothing:  My best crystal
> oscillator
>
> >> is a Symmetricom clone of the double-oven HP 10811s (it came out of an
> HP
>
> >> GPSDO, so apparently HP at one time used them interchangeably with the
>
> >> 10811).  That OCXO uses a 5MHz crystal and a frequency doubler to
> produce
>
> >> its 10MHz output.
>
> >>>
>
> >>> Best Regards,
>
> >>>
>
> >>> Charles
>
> >>>
>
> >>
>
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>
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