[time-nuts] Need a Watch Recommendation

[Bob kb8tq]

Hi


> On Mar 15, 2018, at 1:33 AM, Dana Whitlow <k8yumdoober at gmail.com> wrote:
> 
> I concur with Bill.  And even if one keeps tabs on the current watch error,
> as is the usual practice by celestial navigators, once that error reaches
> or exceeds more than a minute the process frankly gets more clumsy and
> error prone.  And if a watch drifts in time very rapidly, one loses faith
> in its
> ability to coast at a known rate between checks against WWV, which
> opportunities are not always available when one wants, due to
> propagation issues.
> 
> Whatever happened to the quartz watches with trimmer capacitors
> for setting the rate?

Trimmer caps to set watch crystals are problematic. They are a source of error
as well as a set mechanism. You bump this or that and the trimmer moves. They
also cost money to buy and install properly (no flux in-between the plates …). 
Once that is all done you need a way to set them in the factory. Back in the day,
yes, we hat line workers who did that sort of thing. We also sold the crystal in the
watch module (not the whole module) for $2 once upon a time. 

How close do you want to set it? In our case, the set was supposed to be < 0.5 
ppm of the target. Ideally you needed a design that would do a small fraction
of a ppm in a typical situation. 

If the trimmer is a normal device, you get about 120 degrees of travel for the 
useful part of the tuning curve. A tune range of 30 ppm for the crystal and another
20 ppm for the other parts would not be unusual. Even taking the 0.5 ppm number,
you are into 120 / 100 = 1.2 degrees sort of set on that little trimmer. 

Bottom line: They went away because they weren’t good enough and they were
to expensive …. Setting a modern “shoot the chip” register based module is way
more accurate and reliable. It’s silicon so the cost is whatever sand is selling 
for ….

Bob

> 
> And radio controlled?  No way!
> The process is to delicate and marginal to rely upon.  Give me a
> good stable free-running watch any day.
> 
> I don't like the solar watch concept mainly because one sometimes
> has to go for weeks without an opportunity to expose his watch to
> direct sunlight (or some indoor equivalent) for the requisite period
> of several hours.
> 
> Yesterday I was reading the manual for the Citizen ECO series,
> and that thing requires far too much effort and complication to keep
> it working and on time.  A good watch must simply work, with no
> maintenance beyond occasional battery replacements (and possible
> gland replacement at battery-change time), and accurately enough
> that the time need never be reset between battery replacements.
> 
> I use an old quartz diving watch I bought just under 10 years ago,
> (brand no longer distinguishable), which has never drifted more than
> about 30 sec (usually less) between battery replacements, and I never
> take it off between batteries except when compelled to do so at TSA
> checkpoints.  Aside from its LCD's failing I'd be happy to use if forever,
> but it's getting awfully hard to read these days.
> 
> Dana
> 
> 
> 
> On Wed, Mar 14, 2018 at 10:54 PM, Bill Byrom <time at radio.sent.com> wrote:
> 
>> On Wed, Mar 14, 2018, at 6:53 PM, Dr. David Kirkby wrote:
>>> What is the most demanding task one would use a wrist watch for?
>> 
>> It depends on your job or hobby.
>> 
>> During the Apollo 13 rocket burn before their emergency re-entry, Jack
>> Swigert used a wrist watch to time the retrorocket burn which was
>> manually controlled by Jim Lovell. Their normal capsule chronometer was
>> inoperative. This was mostly a differential (time interval) timing
>> measurement.
>> If you needed to determine your location (longitude) and all you had
>> was a wristwatch and a sextant (and software or a table with certain
>> information), the accuracy of the distance calculation would depend on
>> the absolute time accuracy of the watch. At the equator the longitude
>> error due to time error is (40,075.16 km/day) / (86,400 sec/day) =
>> 463.8 m/sec.
>> Amateur astronomers need to know time accurate to about a second or
>> better for accurate osculation observations.
>> Amateur Radio nets and phone, Skype for Business, or WebEx conference
>> calls usually start pretty close to the scheduled time. In some cases
>> people start wondering if the organizer is delayed after about 15 to
>> 30 seconds.--
>> Bill Byrom N5BB
>> 
>> 
>> 
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