[time-nuts] World's most precise.... wall clock

[Peter Reilley]

I was thinking about the discussion on synchronizing a grandfather clock
using a magnet and coil.   Most methods for doing this use an external
power supply or a battery.

What about powering the synchronizing circuit from energy harvested
from the pendulum.   Consider that you can get a quartz watch that will
run for 5 years on a minuscule battery.   Surely there is enough excess
energy to be harvested from the pendulum to exceed the energy available
from such a small battery.

The circuit could use a capacitor for energy storage and eliminate the
battery.   Of course the clock would be only as accurate as the 32KHz
crystal but that should satisfy anyone but a time nut. ;-)

You might have to adjust the pendulum to run a little fast so as to
provide the excess energy for the circuit.   The coil would act to slow
the pendulum each cycle thereby absorbing energy which would be
available to power the circuit.


On 3/10/2021 9:26 AM, Dana Whitlow wrote:
> Hal,
>
> The older (and probably the newer models, too) Trimble Thunderbolt GPSDOs
> have
> a user-adjustable time constant accessible via the serial port using a
> program like
> "Tboltmon.exe" (from Trimble).  I suspect that  "Lady Heather"  may also do
> this.  I
> am fortunate in owning a still functioning PC with an actual hardware RS232
> port
> and a usable O/S (Win XP), so running Tboltmon is a trivial exercise for me.
>
> In addition to time constant, tboltmon also lets one examine (and set,
> where appropriate)
> a large number of other items, and it's reasonably intuitive to use.  I've
> never had to resort
> to a manual. (if there even is one) to do what I needed.
>
> My own experience is that a time constant around 50 sec works best in my
> environment,
> providing the best compromise between filtering PPS jitter from out of the
> unit's GPS
> receiver and tamping down OCXO wanderings due to my home HVAC system's
> cycling.
> Setting a far longer time constant value (say, much longer than 500 sec)
> tends to lead
> to "funny business" so I just don't go there.
>
> I have convinced myself that the PPS output from my Tbolt is derived from
> the produced
> 10 MHz output, because if I trigger an o'scope from the PPS output, the 10
> MHz sinewave
> shows very little time jitter, perhaps 1 or 2 nsec.  So, I'm pretty happy
> with the T'bolt, with
> two (minor) exceptions:
>
>>   Its RF sensitivity seems rather poor compared to that of "modern"
> receivers (my unit
>      was apparently made in the early 2000s).
>
>>   In tboltmon, the signal "strength" indications are displayed in units
> called 'AMU',
>      for which I've been unable to find a definition.
>
> Dana
>
>
> On Wed, Mar 10, 2021 at 6:53 AM Hal Murray <hmurray at megapathdsl.net> wrote:
>
>> kb8tq at n1k.org said:
>>> The gotcha here is that if you want accurate *time*, you are better off
>> using
>>> the sawtooth corrected output from a (good) GPS module rather than a
>> GPSDO.
>>
>> Why is that?
>>
>> I would have guessed that a GPSDO would average over many GPS pulses thus
>> reducing the noise.
>>
>> Is it something like GPSDOs are normally designed for good frequency
>> rather
>> than good time, so when they find the time is off, they use a small
>> frequency
>> offset for a long time to correct rather than a big frequency offset for a
>> short time?
>>
>> Are there any GPSDOs designed for good time?  Or any with parameters that
>> can
>> be tweaked to provide good time?
>>
>>
>> --
>> These are my opinions.  I hate spam.
>>
>>
>>
>>
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