[time-nuts] Measuring the accurcy of a wrist watch
Ulrich Bangert
df6jb at ulrich-bangert.de
Thu Apr 17 08:14:39 UTC 2014
Chris,
I do not own a guitar with single coil pickups but I will surely give it a
try to find out whether the humbuckers of my Gibson Firebird & SG Standard
will also do the trick!
Best regards
Ulrich
> -----Ursprungliche Nachricht-----
> Von: time-nuts-bounces at febo.com
> [mailto:time-nuts-bounces at febo.com] Im Auftrag von Chris Albertson
> Gesendet: Mittwoch, 16. April 2014 20:56
> An: Tom Van Baak; Discussion of precise time and frequency measurement
> Betreff: Re: [time-nuts] Measuring the accurcy of a wrist watch
>
>
> I just did an experiment. Place a simple quartz movement
> wrist watch on top of a Fender Stratocaster guitar. I get a
> very strong and easy to detect signal. A loud and sharpt
> "ping" once per second. More then 1 volt
> peak to peak. I can cancel almost all the background hum
> and hiss in the
> normal way by using the selector switch on the guitar.
>
> The guitar has a pickup coil with many thousands of turns of
> #40 wire. With the selector with at #2 position there is a
> second coil some inches away that is wound in the opposite
> direction and the two are added canceling any field that is
> filing the room.
>
> I tried the same with a wall clock and all I had to do was
> hold the clock an inch away. The wrist watch was placed on
> top of the strings a few mm above the bridge PU.
>
> These is likely about 3 oz of #40 magnet wire on a guitar PU.
> If I were building a sensor I'd do it just like the guitar.
> one coil to pick up the signal and another identical coil
> some inches away to to pick up ambient "noise" and then wire
> the two in parallel but in anti-phase.
>
> If yu happen to have a guitar around, you have a watch sensor.
>
>
> On Wed, Apr 16, 2014 at 10:43 AM, Tom Van Baak
> <tvb at leapsecond.com> wrote:
>
> > > Tom,
> > >
> > > can you explain what exactly you understand by "a large coil of
> > > wire"?
> >
> > Sorry, by large I meant a large number of turns; the coil itself is
> > quite small. Rather the winding one myself I just used the
> pickup coil
> > from an old cheap plastic self-impulsed pendulum clock. The wire is
> > extremely fine and there must be thousands of turns since the spool
> > diameter is only 15-20mm and the net resistance is 3.5k.
> Here are some
> > iPhone photos I just
> > took:
> >
> > http://leapsecond.com/pages/Junghans/coil.htm
> >
> > > Did you make the easurements on the Junghans with a DIY sensor or
> > > with
> > one
> > > of the commercially available?
> >
> > Both. The commercial ones sold by Bryan Mumford are excellent; his
> > instrument includes signal conditioning, adjustable high gain, and
> > other useful features. It's meant for watchmaker types with no
> > electronics background. It works perfectly out of the box.
> >
> > The Junghans wristwatch is extremely well engineered for
> long-life and
> > the leaked magnetic signal is the weakest of any watch I've
> measured.
> > Still, it can be measured. The placement of the pickup coil on the
> > watch face needs to be optimized for best "reception", or any
> > reception at all for that matter.
> >
> > By contrast, a typical AAA-battery desk/wall quartz clock movement
> > generates a huge magnetic signal. It is so clean that you
> can clearly
> > see both the start (+) of the impulse and the end (-) of
> the impulse
> > about 30 ms later. In fact I suspect it's actually 31.25
> ms, or 1/32
> > s, since that's 1024 cycles of a 32.768 kHz oscillator. See:
> >
> > sensor placement:
> > http://leapsecond.com/pages/Junghans/quartz-clock.jpg
> > output to scope: http://leapsecond.com/pages/Junghans/coil-aa.gif
> >
> > > I have made some basic tests with a coil coming from a
> loudspeaker's
> > cross
> > > over network. It has a few hundred windings, R=1.3 Ohms,
> 2.3 mH, but
> > > the only thing i receive with this coil is a strong 10 Mhz
> > > signal...perhaps
> > no
> > > real surprise in a time nuts laboratory.
> >
> > I suspect your 1.3 ohms means the number of turns is far too low. I
> > don't see any RF here, nor even very much 50/60 Hz.
> >
> > /tvb
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>
>
>
> --
>
> Chris Albertson
> Redondo Beach, California
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