[time-nuts] Re: Custom Quartz crystals

[Donald E. Pauly]

All crystals are series resonant.  Some are merely cut for resonance
with an external capacitor such as 30 pFd.  The crystals in my designs
operate solely at series resonance and an external capacitor is not
specified. Q is a function of the care in manufacturing and affects
pullibility. Angle of cut determines the upper turning point
temperature.  Standard AT cuts have a 65° turning point.
That turning point is also affected by the overtone of operation and
is different for fundamental and 3rd overtone.  5th and higher
overtones have nearly the same turnover temperature compared to 3rd
overtone.  See https://gonascent.com/papers/crystals/xtlcurve.jpg

On Sun, Aug 14, 2022 at 10:27 AM Corby Dawson via time-nuts
<time-nuts at lists.febo.com> wrote:
>
> Thanks for the advice, I'll see if those companies can help.
> I am wanting to replicate the oscillator circuit  at
> http://www.wa1mba.org/PLLVCXO/stephensen.pdf
> but at 60Mhz. The article specifies...
>
> "Y1 is a
> fifth-overtone, AT-cut crystal ground
> for operation in the series-resonant
> mode with a load capacitance of 30 pF"
>
> I thought that a series resonant crystal did not have a load
> capacitance??
>
> I'll send this info along to the Crystal manufacturer and see what they
> say.
>
> I had bought an FE 2216A OCXO oscillator of eBay a couple years ago
> thinking of this same project however it has a 120Mhz output.
> I read that a lot of these higher frequency oscillators had a fundamental
> that was doubled.
> So I opened it up hoping to find a 60Mhz crystal.
> Once the potting was removed I could see a Minicircuits doubler on the
> bottom of two boards and scopeing it showed 60Mhz in!
> However the oscillator/oven board has a 5Mhz SC cut crystal and a hybrid
> module that gets it up to the 60Mhz! See PIX.
>
> While trying to find a crystal I'll use this board to test out my scheme!
>
> Cheers,
>
> Corby_______________________________________________
> time-nuts mailing list -- time-nuts at lists.febo.com
> To unsubscribe send an email to time-nuts-leave at lists.febo.com