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

paul swed paulswedb at gmail.com
Thu Jun 27 20:13:28 EDT 2013


Yes it makes a very fine 35 Mhz oscillator and reasonably stable.
Been there and done that.
Hey the systems done. May remod it one day but bigger fish to fry with the
d-psk-r
Regards
Paul
WB8TSL


On Thu, Jun 27, 2013 at 6:41 PM, David McGaw <n1hac at alum.dartmouth.org>wrote:

> Lower gain is better as long as it oscillates.  The 74HCU04 is unlikely to
> drive spurious responses.  The 74HC04 is OK as long as you keep the
> feedback gain low - sometimes a series resistor from the output to the
> resonant circuit is required.  A 74HC14 is the WRONG part for the job as it
> can and will oscillate without the crystal controlling it - just try it
> with a resistor for feedback and a capacitor to ground at the input, no
> crystal.
>
> David N1HAC
>
>
>
> On 6/27/13 6:30 PM, paul swed wrote:
>
>> I will say the fact is the 74hc14 is a bit of a power pig we are talking
>> 12
>> ma. The rcvr is something much less like 100 ua. At least for the moment
>> it
>> all works but 12 ma is a pig.
>> Especially when you take the signal out and knock it down to 100-200 uv.
>> Regards
>> Paul.
>>
>>
>> On Thu, Jun 27, 2013 at 5:37 PM, ed breya <eb at telight.com> wrote:
>>
>>  Still having email problems - here we go again. This is second try,
>>> please
>>> excuse if both show up.
>>>
>>>
>>> Hal Murray said:
>>>
>>>> They make 74xU04 for many values of x.  The U is for Unbuffered.  They
>>>>
>>> have
>>> lower gain in the linear region.
>>> I thought they were intended to be used for things like this, but I don't
>>> understand that area.  Can anybody give me a quick lesson or point me at
>>> a
>>> good URL?<
>>>
>>>
>>>
>>> I always thought the unbuffered "U" versions were preferred for ring
>>> oscillators mostly to save power - you don't want the high-drive output
>>> stages to be cooking away in linear mode if not needed. The propagation
>>> delay can also be less since the U ones have only one stage instead of
>>> three (the building block is the totem-pole inverter stage), but they
>>> can't
>>> drive very much load anyway. I think that most MSI and LSI parts that
>>> have
>>> built-in ring/crystal oscillator sections use the U topology, but I don't
>>> think there's anything special about it - it's the simplest thing that
>>> works.
>>>
>>> I've made quite a few CD4000 and 74HC oscillators, and never worried too
>>> much about U versions or not, except for battery-run items where power is
>>> critical (or you can run the oscillator at lower voltage). Often they are
>>> made from inverting gates that are part of a shared package, where you
>>> wouldn't want puny drive capability in the other gates anyway. They are
>>> relative power hogs though, whenever linear biasing is needed. Except in
>>> the 4000 series, I don't know if U versions are available in anything but
>>> the '04 hex inverter, but I suppose it's possible. I think the
>>> Schmitt-trigger types like HC14 are necessarily buffered, so have three
>>> stages, since you need a non-inverted version of the signal for the
>>> positive feedback to the input.
>>>
>>> I've never tried making one in 74AC - I don't know if it's even possible
>>> to bias one up that way without it burning up. I'm working on some
>>> related
>>> circuits now, so maybe I'll set up an experiment to see how much current
>>> it
>>> would take for one inverter - I've often wondered about this.
>>>
>>> I read about this years ago in various CMOS application notes, so I may
>>> be
>>> missing some key points - there should be plenty of info online. The
>>> older
>>> generation (when CMOS was fairly new) info may provide more detail about
>>> the guts than that related to the newer, higher performance families.
>>>
>>> Ed
>>>
>>>
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