[time-nuts] wwvb 60 khz tuning fork crystals Some insights

paul swed paulswedb at gmail.com
Thu Jun 27 13:02:46 UTC 2013


To answer the several questions. It is a 74hc14.
Burt the feedback resistor is 22M
The xtal drive resistor is below 270K.
So think of it actually as a 22 M in parallel with in my case about 200K.
Granted the series drive leg has a 230pf cap to ground next to the xtal and
then the xtal in series to pin1.
Ed good comment on the 74c04. May tinker with that. Though the HC14s
working pretty nicely now.
What I find odd is that the traditional 2 caps to ground with one being
variable created very very slow startups or unstable startup.
Last comment yes indeed those crystals are small.

Regards
Paul
WB8TSL


On Thu, Jun 27, 2013 at 12:17 AM, ed breya <eb at telight.com> wrote:

> Email still seems to not be getting through - it seems like sending twice
> works sometimes. Here this one goes again - sorry if it shows up twice:
>
> I presume you used the regular 74HC04 or 74HCU04 inverter, not the 74HC14
> Schmitt trigger input type?? If the '14 is actually used, that may explain
> the problems around setting the feedback biasing resistor value - you may
> be overriding the built-in hysteresis to get it in the linear region.
> Usually that R isn't very critical with regular crystals, but maybe tuning
> fork types need more gain, or, if it's actually a '14, the input impedance
> is probably lower than a regular gate, so it's loading the resonator.
>
> Ed
>
>
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